View Full Version : Three-Phase Current Chopping, Eddy Current Brake

el bob
01-09-2009, 12:35 AM
Hi all,

I am working to add computer control to an aging eddy current engine dynamometer. You can see pictures of the engine dynamometer and original instrumentation here if you're interested. (http://kai.caltech.edu/MotiveEngineDyno/)

I scanned a copy of the original schematic from 1979. It spanned 5 A4 European size pages. I grafted it into one jpeg and you can see it here. (http://kai.caltech.edu/MotiveDynoController/09_01_04-1348-FullStitch-Cropped.jpg)

I am ultimately trying to figure out what the RC, SC and TC signals going into the 6'024'0 controller board (see schematic/photos) look like and how to emulate them using computer output. At this moment, I am trying to figure out what one of the pieces on the 6'024'0 circuit board is. It looks like a TO-92 transistor. I tried searching the printed text on Google but could not find anything. Does anyone recognize it?


The top line in the "T" in TEC looks more like a squiggly, wavy sketch artists use for far-away birds. That's a terrible description, but the point is it's not a regular T. :)


As you can see on the schematic, the details of the 6'024'0 circuit are not shown. I removed the board from the controller to document it. I put together a schematic that is accurate, setting aside the unknown transistor. I tried to draw the transistor into the schematic, orienting it so the leads coming out of it go in the same direction as they do in this photo. (http://kai.caltech.edu/MotiveDynoController/60240_Removal/images/image/IMG_2435.JPG)

Updated 6'024'0 Controller Schematic v2.0

6'024'0 Controller Schematic v1.0

Dynamometer Photos

Eddy Current Controller Schematic

Eddy Current Controller Photos

6'024'0 Controller Removal Photos

Unknown Transistor Photo

01-09-2009, 01:08 AM
I believe the logo is for Tecor. The part appears to be an SCR - http://www.datasheetarchive.com/EC103A-datasheet.html.

How good is that schematic? Can you tell what the leads go to? The callouts appear to be for thyristors (g = gate, k = cathode). I would think the brake would need devices in larger than TO-92 to switch current.

Love the shopping cart full of rocker arm assemblies and cams.

el bob
01-09-2009, 02:17 AM
Beenthere, thank you very much! That is a great help.

There are three larger SCR's bolted to the 6"x2"x1.5" aluminum heatsinks. They are more visible in these photos.


Shopping carts are surprisingly strong and always useful. I know a guy who uses them by the half-dozen as an instrumental part of an exhaust system production shop. I'm with you though, nothing better than one with a camshaft sticking out of it.

el bob
01-09-2009, 02:32 AM
Thanks to Beenthere again

Updated 6'024'0 Controller Schematic (v2.0)

el bob
01-09-2009, 02:37 AM
ow good is that schematic? Can you tell what the leads go to? The callouts appear to be for thyristors (g = gate, k = cathode). I would think the brake would need devices in larger than TO-92 to switch current.

Are you talking about where the leads on the pdf schematic go to? They match up to the leads going into the 6'024'0 empty white box on the complete controller schematic jpeg file. (Warning, 3MB)

Eddy Current Controller Schematic

Starting from the top right of the large jpeg schematic, the incomplete 6'024'0 drawing begins about 20% in from the left, and about 25% down from the top. It shows leads for R3, S3, T3, RC, G, K, SC, G, K, TC, G, K, 20, and 0.

I hope I understood the question correctly.

01-09-2009, 12:23 PM
Got the schematic, but no time to look it over for a bit. Do you have an oscilloscope? It could be a handy tool to look at those line and relate their activity to the action of the braking.

el bob
01-09-2009, 12:37 PM
With the 6'024'0 circuit schematic complete, the issue I'm facing now is understanding how the 6'024'0 circuit works with the three larger SCR's (seen on the complete controller jpeg schematic) to control current sent to the Brake Coil.

I read the allaboutcircuits.com article on SCR's. (http://www.allaboutcircuits.com/vol_3/chpt_7/5.html) It seems that the current is being controlled by "chopping" the AC signal so that only parts of the positive phases are allowed to continue towards the brake coil. What I don't get is what kind of signal input on the RC, SC, and TC terminals, the inputs to the 6'024'0 circuit, results in variable control of the larger SCRs inline with the 380VAC lines going to the brake coil.

Eddy Current Controller Schematic (jpeg)

Updated 6'024'0 Controller Schematic v2.0 (pdf)

I'm also a little confused by the grounds on both circuits. I'm not familiar with positive-ground systems, and I'm not sure this is one, but I'm planning to read a little bit into that. Any insight there would also be greatly appreciated. Happy Friday all.

01-09-2009, 05:50 PM
Can you relate the G, K and C (that would be RC, etc) to the fastons located on the PCB? They are probably the lines the dyno uses to trigger the small SCR's that in turn fire the big ones - but it would be good to check.

Too bad that controller is a black box. No Italiano, anyhow.

el bob
01-09-2009, 06:55 PM
Ah, I missed your post this morning somehow. Yes, I was able to find the G, K and C leads shown on the schematic inside the real-life controller. Finding these wires helped me identify which circuit board was the 6'024'0 board. I then removed this circuit board and drew up a schematic for it, linked to here as a pdf and jpeg file.

The three G, K and C sets of leads (G, K, RC, G, K, SC, G, K, TC) going into the "black box" are included in the 6'024'0 pdf and jpeg documents. The complete details of the black box are shown in the 6'024'0 pdf schematic. I converted the 6'024'0 schematic pdf file into a jpeg file as well, in case it is easier to view.

Updated 6'024'0 Controller Schematic v2.0 (jpeg)

I do have an older Tektronix 2 Channel oscilloscope, but I have not been able to hook it up yet. As you can see in the dyno room pictures, the equipment is tucked away very tightly when all the dyno pieces are installed and ready to run. I am thinking about soldering in three test leads into the RC, SC and TC leads to run outside of the controller's box. These wires would let me tap into the signals easily even while the box is bolted up and installed in the equipment rack. I don't really know what to expect over the RC, SC and TC leads. I'm hoping the oscilloscope won't mind whatever it is. I have two 10x attenuation probes.

I currently have the complete eddy current controller apart on a bench. Most aspects have been covered in photos. I'll have to reassemble the controller and reinstall it in the rack before I can run the dyno and scope the 6'024'0 input leads.

01-09-2009, 07:47 PM
What is the operating proceedure for the dyno? How are measurements taken? I can see a load cell in one photo.

You might want to measure those leads to ground before you attach the o'scope leads. You don't want to let the smoke out of the case.

el bob
01-09-2009, 08:22 PM
I'm glad you mentioned grounding the leads. The system appears to have a positive ground. Do I reference RC, SC and TC to the positive ground? I'll make sure to check them out with a DMM first. I'd like to keep the smoke inside the scope's case for at least a little while longer.

Regarding operating procedures for the dyno, I'm not sure how much detail you are looking for. Just let me know which areas could use more description.

Dyno Data Acquisition Overview

The load cell you see is the sensor used to ultimately measure torque. There is an Omega OM5 full-bridge strain gage signal conditioner and an OM5 two-channel backplane. The strain gage signal conditioner module supplies 10VDC excitation voltage to the load cell, processes the load cell's output signal and provides a 0-5VDC scaled analog output representing 0-2500lbs on the load cell. This 0-5VDC analout signal is wired into an RS232 DAQ (Innovate Motorsports SSI-4) which applies a calibration formula to convert the 0-5VDC signal into a real Torque value to be analyzed by the dyno operator.

The only other sensor at this point in time is a variable reluctor positioned very close to the outer radius of a 60-0 toothed trigger wheel. This sensor produces a 0-80VAC sinusoid whose frequency variers with the rotational speed of the trigger wheel, which is mechanically fixed to the RPM of the test engine and dyno assembly. The two wires from the VR sensors are connected to special leads on the DAQ that feed into an onboard VR signal amplifier circuit. The DAQ reads the frequency of the signal. Due to the fact that this specific trigger wheel has 60 teeth, the magnitude of the frequency equals the magnitude of the RPM.

VR_Signal_Frequency(Hz) x 1_Revolution/60_Trigger_Wheel_Teeth x 60_Second/Minute = RPM

1_Revolution/60_Trigger_Wheel_Teeth x 60_Second/Minute = 1 ----> VR_Signal_Frequency(Hz) = RPM

A computer runs software that interfaces with the DAQ and records the Torque and RPM measurements. The software calculates Horsepower on the fly according to HP=Torque*RPM/5252.

Dyno Load Application Overview

The test engine is first started up with the dyno "off," meaning no current is passing through the Brake Coil and no load is on the test engine. The existing manual eddy current brake controller has its own VR sensor that gives it an RPM feed. The controller is switched on and then a knob is turned to apply more or less load. There is also a separate knob to switch load application modes. Some modes multiply the selected amount of load (selected with the first knob) against the sensed RPM. I can scan the operator's manual for the dyno brake controller, it is only two pages.

The RPM and Torque output of the test engine can then be controlled by varying the mechanical Throttle input and the load knob on the brake controller. The problem and motivation for the project is to allow for computer control of load application so that consistent, back-to-back tests can be run with the same load application. It will also allow for control of when and how much load to apply in these tests.

01-09-2009, 08:44 PM
I can see where that would be desirable. The computer may need to have some of the other inputs led in before it can really control the system.

That's a bit later - I'm looking over the wiring diagram in between all else to try to make sense of some different electrical conventions.

"All else" meaning all the other stuff going on.

el bob
01-11-2009, 02:55 AM
I tapped in some "T" connections in the RC, RG, SC, SG, TC, TG and 0 (positive ground) lines and brought the oscilloscope in for testing. Pictures of the wires being added and the test being setup in the dyno room are linked here. (http://kai.caltech.edu/MotiveDynoController/BrakeControllerOscope/)

There were two main tests. The first involved scoping between RC and 0. The second involved scoping between RG and 0. The idea here was to try and gather some clues as to what sort of input on RC corresponds to what kind of output on R's G terminal that ultimately actives the inline 380V AC SCR.

Pictures, description and results for the RC & 0 oscilloscope testing. (http://kai.caltech.edu/MotiveDynoController/Oscope_RC/)

Pictures, description and results for the Rg & 0 oscilloscope testing. (http://kai.caltech.edu/MotiveDynoController/Oscope_RG/)

Does this give anyone any ideas as to what kind of signal could be used on the RC, SC and TC terminals to gain variable control of current going to the brake coil?

01-11-2009, 01:36 PM
The magic is all in the black box section - the board labeled 0'046'0. The 34 volt transformer feed all three phases into ii on pins Rb, Sb & Tb. Something inside the board decides how much current is wanted in the brake, and pulses the small SCR's on - which in turn fire the big SCR's. The few controls shown do not seen to be related to the brake function in any way.

Your photos of the pulses on the Rc, etc lines will be more meaningful is the second trace shows the b input as a timing reference. The earlier in the positive cycle the pulse occurs, the more braking - or so it appears.

A circuit called a zero crossing detector can indicate when an AC waveform is at 0, and simple timing can calculate how long to delay after the crossing before pulsing the SCR on.

What might be interesting is the thought of using the computer to run the whole test. That will require many more inputs and a control program. Using the computer as a stand in for the control board is kind of overkill, but using it to run a testing loop is pretty sensible.

el bob
01-12-2009, 02:23 AM
Thank you again for your insight. I did not think about the 34V AC lines going into the 0'046'0 circuit before, but it seems obvious that they are used as a reference for control of the Rc, Sc and Tc outputs now that you mention it.

I have been looking into possible control solutions today. From my reading thus far, it seems like a combination of National Instruments LabView software and an NI DAQ makes for a popular platform.

My current idea is to use the 440V, 380V and 34V AC power supply portions of the existing dyno controller and add a new computer-based controller that outputs to the little SCR's.

Are there any off-the-shelf pieces that can take in a scaled analog input (say, 0-5 or 0-10VDC) and separately fire the three little SCR's with phase delays proportional to the input voltage? It would have to monitor the incoming Rb, Sb and Tb waveforms to know when to trim and fire the three phases.

If such a piece exists, or if something close enough exists, then I believe feeding RPM, Torque, and possibly coil input current data into LabView will allow for a decent eddy current dynamometer controller. LabView can run a PID controller that would tie into one of the DAQ's analog outputs, ultimately controlling the piece that fires the little SCR's.

01-12-2009, 01:38 PM
I found a link to an article by Teccor that deals with phase control SCR switching - www.eetasia.com/ARTICLES/2001JUN/2001JUN14_AMD_AN5.PDF.

Since it appears that the small SCR's trigger the big ones, it seems pretty likely that triggering the small ones from a logic gate is going to work. I will hunt around for indications of OTC controllers - chances are good that they exist.

01-12-2009, 06:02 PM
Doing some digging online, I came across these people - http://www.appliedps.com/newweb/Datasheets/AP-1950/AP-1950.htm.

The controller would replace all but the big SCR's in your dyno, and might make control from a computer or microprocessor pretty simple. The Google search term was "three phase scr control circuit", if you want to look further. Something like this would make automation of the dynomometer considerable easier.

el bob
01-12-2009, 08:30 PM
Thank you beenthere. Google digging can be quite an exercise.

I searched around a bit after reading your earlier post this morning. It took me a while to figure out the most appropriate Google search terms, but I eventually stumbled into Eurotherm, Practical Global Solutions, ISE, Wayne Engineering and finally Applied Power Systems.

I spoke to Les @ Applied Power Systems. The BAP1950 sells for $450 configured as a half controller in singular quantity. That will work.

I had actually jotted down a few questions I was going to ask, one of which was whether the AP-1950 should be used to trigger the small SCR's, or bypass the small SCR's and trigger the large SCR's directly. You can imagine my surprise to come back to this thread and see, not only had you already nailed the product choice, but also figured out the most logical implementation as well. Any chance you have a pick for the SuperBowl? :)

I ordered a book on LabView and printed out the NI LabView PID Toolkit manual. I need to read a bit and then it should be possible to lay down some kind of plan for the combined LabView, DAQ and SCR Firing Board system to control the dyno. I printed the Teccor article on Phase Firing you posted as well.

01-12-2009, 09:00 PM
It will be nice it it works for you. I didn't think you wanted to try to build something from scratch, and that controller looked to be pretty flexible as to actual control scheme.

You might want to keep the old control panel for bragging rights, though - "used to check out Ferrari engine rebuilds with it".

el bob
01-13-2009, 02:19 AM
It's funny you mention that. There are a couple of Ferrari engines that may see use on the dyno if a decision is made to install gearing that allows gas motors to rev higher than the dyno's 3600RPM limit. Most of the motors going on the dyno are 6.5L+ diesels, so the RPM limit is usually not an issue.

Now that you mention it, I was intending to install a switch that could allow the dyno to be controlled by either the Computer or by the existing Sicon Controller. This way the dyno could still be operated with the manual controls, as it currently is today, in the event there is ever a problem with the new computer. I havn't planned out the actual mechanism or begun to consider any possible ill electrical effects of using such a switch, but it's something that, I believe, would provide considerable value. The most basic idea would be to use a two position, six terminal mechanical switch, but that may not be a great idea. Any pitfalls to avoid that you can see there?

01-13-2009, 05:57 PM
Not without knowing more about the black box part. You "should" be able to simply switch the three leads to the main SCR's and run under the new controller. Even if the old box is trying to send signals, it shouldn't bother the small SCR's to have no load.

You might want to use a three pole double throw toggle with a guard on it to make sure it doesn't get bumped while testing. An accidental change in load could lead to engine disassembly.

el bob
01-15-2009, 08:41 PM
I am attempting to spec out suitable DAQ hardware to both sample Torque and RPM data, as well as output a 0-5V DC analog control signal for the SCR firing hardware. I'm looking at DAQ's that include analog out channels. One of the DAQ specs I'm focusing on is the maximum analog-out samples per second output rate.

National Instruments (NI) USB-6211 (http://sine.ni.com/nips/cds/view/p/lang/en/nid/203224) has two 16bit, 250kS/s analog out channels. If the SCR firing board has to make a decision on how to phase control three-phase AC lines operating at 60Hz, then it has to make at least 180 decisions in one second. Following this idea, is it possible for the SCR firing board to even make use of input control data at a frequency greater than 180Hz?

I'm trying to determine if there are best practices to follow, or more importantly common mistakes to avoid, when deciding the speed at which the complete LabVIEW dyno brake PID controller will output a control signal. Is there a parallel to the Nyquist rate on the signal input and sampling side? I am searching on Google, but appear to have not hit the right keywords yet.

01-15-2009, 11:41 PM
From past experience, 16 bit data is hard to get outside a lab. That's 1 part in 32,768, which is very precise, but also prone to noise.

We have had some issues with the DI-720 acquisition device (we being myself and a researcher in California), but the DI-730 - http://www.dataq.com/products/hardware/di730.htm - is worth a look. Just put shorting bars in unused inputs.

14 bits gets 1 part in 8096 resolution, plus the 730 has more robust input protection. Look at the literature and talk to the people.

One way around the Nyquist limit is to sample way above it. Your RPM sensing will be a multiple of the actual, for instance. You might want to sample at 10X the max rate to see if the rate wanders a bit over time. It becomes mind-boggling to realize the things you can do with a good digital system.

el bob
01-16-2009, 01:24 AM
That 730 unit is very impressive. "Measurement range of ±10mV to ±1000VDC (or peak AC) over six ranges" The idea of being able to monitor the brake coil's input current and voltage directly without additional hardware is enticing.

On the other hand, it is $3,000, and somewhat less importantly, does not provide an analog output. I believe that price is very fair for what it is. Eight 14bit channels that can be sampled simultaneously at 150kHz make for a great feature set. I am hoping that I do not need that much capability. Looking through the DataQ data acquisition product line (http://www.dataq.com/products/hardware/index.htm), I do not see units with analog output channels. Were you thinking about using the 730 for input and a separate module for the control signal output?

Initially, the only input channels will be the 0-5V DC signal from the strain gage signal conditioner (feeding from the load cell) and a -50 to +50 V AC waveform from the variable reluctor crank trigger sensor. The frequency of the AC signal will vary from 0Hz to 3600Hz, directly (1:1) related to the RPM of the dyno and engine under test. Following the Nyquist limit, the minimum sampling rate necessary for the RPM data is 7200Hz. It seems that most data acquisition boxes outside of the <$200 range offer sampling rates orders of magnitude larger than this.

As of right now, the plan is to run the PID loop solely off of RPM data, namely the difference between target RPM and instantaneous RPM. It would be nice to incorporate brake coil voltage and current checks into the controller, but I don't see that in the cards right now. There may be an essential reason to act on it, perhaps something safety-related, but I can not think of one right now.

01-16-2009, 04:30 PM
It is kinda interesting to find it all in a box, plus I lost sight of the analog control function.

See what you think of the stuff here - http://www.circuitspecialists.com/level.itml/icOid/107.

I think USB connected controllers are great, as they are computer-independent, but this stuff looks good for the analog control.

I'll have some time to look further, so check back...

01-16-2009, 06:14 PM
A few sites to consider:



http://www.bb-elec.com/product_family.asp?FamilyId=286&Trail=4&TrailType=Top (look at the USB -4711)

Like all else on the internet, the choices look infinite. I was using the search term "analog interface module with usb i/o". You will need 12 - 14 bits resolution in the D to A, and at least 10 bits in the D to A output. Have extra channels in and out available - you may find it will be interesting to monitor more stuff for better dyno results.

el bob
01-16-2009, 07:00 PM
I think you are on to something regarding USB and portability. I do most of my developing and testing on a laptop a few miles from the dynamometer itself. The dedicated dynamometer PC is a desktop and has open PCI slots. I could use PCI DAQ hardware, but I won't be able to do very much bench testing away from the test cell. A USB DAQ would allow for basic LabVIEW testing with a laptop. This could minimize the amount of time the dynamometer will be unavailable for use while the new brake controller is installed, configured and tested.

Thanks for posting the Circuit Specialists link. I read through the NuDAQ product list. It's all PCI hardware, which again could work, but may not be the best fit. I noticed that the DAQ units are advertised as "Continuous, gap-free, high speed under Win-NT/95." I see there's a driver that supports Windows98/NT/2000/XP. I clicked on the "Very Important Information for LabVIEW™ Users" (http://www.circuitspecialists.com/prod.itml/icOid/7779) link. There's a screenshot of the product being used in LabVIEW, but it appears to be a much earlier version. It probably works with the latest version of LabVIEW as well, but it may not be the selling point of the line. The $399 eight channel analog output PCI card looks like a great value for the price, but there isn't mention of driver support for Windows XP.

I am reading through the three new links posted above. I have used Measurement Computing USB DAQ hardware in the past with LabVIEW. It worked well. The USB-1408FS (http://www.measurementcomputing.com/cbicatalog/cbiproduct.asp?dept%5Fid=413&pf%5Fid=1757&mscssid=WV6KUJ3NGHRC8P6RQSWV1ALEAWQN8HP0) is tantalizingly affordable at $249, with four 14bit differential analog inputs and two 12bit analog outputs. Adding additional analog input channels, and keeping analog output capability, knocks the price up $1150 to $1,399 for the USB-1608HS-2AO (http://www.measurementcomputing.com/cbicatalog/cbiproduct.asp?dept%5Fid=413&pf%5Fid=1828&mscssid=WV6KUJ3NGHRC8P6RQSWV1ALEAWQN8HP0). It's interesting that a 100% increase in analog inputs channels results in a 561% increase in price.

The B&B Electronics website does not mention LabVIEW compatibility. It's likely that it's compatible, but I don't see it on the product description page. It looks like I need to set up a web account to see pricing on the Intelligent Instrumentation products.

Among the NI USB DAQ contenders, I'm weighing the benefit of the "Industrial" USB-6221 (http://sine.ni.com/nips/cds/view/p/lang/en/nid/203093) versus the portable USB-6211 (http://sine.ni.com/nips/cds/view/p/lang/en/nid/203224). The former uses a standard 120VAC power source. The 6211 gets its power over the USB connection. Needing a 120VAC power source is not a probem for this installation, but the 6221 costs $200 more at $1049 versus $849 for the 6211. They both offer the same analog inputs (8x 16bit differential @ 250kS/s). There is a difference in analog output current drive capacity. The 120VAC unit can put out 5mA while the portable unit puts out 4mA. I can't understand why the unit with wall power can't drive more current. I don't know for sure, but I think the analog control signal will not require more than either of these amounts of current. Does that sound about right?

There must be a Measurement Computing unit that's priced between $1399 and $249 that has analog outputs. If there really isn't, I'll probably go with either the NI 6211 ("Portable", USB Data + USB Power) or 6221 ("Industrial", USB Data + 120VAC Power).

el bob
01-16-2009, 07:11 PM
Something I didn't mention is that it looks like the Variable Reluctur (VR) RPM signal will need to be passed through a signal conditioner before heading to the USB DAQ's being mentioned. The NI DAQ's have maximum voltage ratings of -5..+5 and -10..+10 Volts. The unmodified VR signal can rise above 50V.

There's a circuit made for MegaSquirt projects that converts two VR signals into square wave signals. I believe they are 0V/5V signals. It's made by Jean Bélanger and is available for sale from his web site. "Dual VR Conditioner Board v1.1" (http://jbperf.com/dual_VR/index.html) There is no schematic posted on JB's site, but there's a link to the MegaSquirt web page describing the circuit it's based on. (http://www.msextra.com/manuals/MS_Extra_Ignition_Hardware_Manual.htm#2ndVR)

Does that look like the output signal voltage will stay below 5V?

el bob
01-16-2009, 07:46 PM
I previously thought the $200 difference in price between the NI USB-6211 and USB-6221 was the result of the "Industrial" build of the 6221. After reading the spec sheets again, I noticed that the 6221 offers twenty-four digital input/output channels compared to the 6211's four. The 6221 also has 24mA maximum current drive for each of these digital channels compared to the 6211's 16mA.

It seems that most of the $200 differences goes towards increased digital I/O capabilities that are not necessary for this application. I foresee needing more analog input channels in the future, but not necessarily digital channels. Given this, between the two, I would opt to save the two hundred dollars.

I double-checked the Measurement Computing product list. The options listed two posts above are the only applicable choices. Both have two 16bit analog output channels. There is the option of four non-simultaneous analog inputs for $249, or the option of eight simultaneous analog inputs for $1399. Too bad there isn't a unit with specs similar to the NI-6211 for $400-$700. Since there isn't, I'll probably go with the NI-6211.

01-16-2009, 08:30 PM
With off-the-shelf, life is compromise. You wonder why some hardware costs like NASA-grade, and some is a fraction of that cost, but always with one significant feature absent.

That variable reluctor signal would go into a digital input better than being converted by an A to D. If it's going 0 - 5 volts, it's already digitized to the extent you require, which is to signal that another tooth has come opposite the sensor.

Save the A to D inputs for the torque-measuring bridge and things like head and exhaust temperatures, manifold pressure, etc.

el bob
01-17-2009, 03:40 PM
The equipment list seems to be settling.

Applied Power Systems BAP-1950 (SCR Firing Module)
National Instruments USB-6211 (USB DAQ with Analog & Digital I/O)
JBPerf VR Conditioner (AC VR Signal -> Digital TTL)

I've got the Sicon controller box (reference picture) (http://kai.caltech.edu/MotiveDynoController/BrakeControllerOscope/images/image/IMG_2515.JPG) apart to plan the connections necessary to add in computer control. I'm looking at the BAP-1950 Datasheet (http://kai.caltech.edu/MotiveDynoController/BAP1950.pdf) and figuring out which wires need to be hooked up inside the Sicon box. The BAP-1950 needs to connect to the gate and cathode of each SCR in a "DC Power Supply - Half Control Converter" configuration. The big SCR's in the Sicon box have four connections.

ThreePhase Line In (Anode) ||Not Visible in Pictures
ThreePhase Line Out (Cathode) ||WireColor=Black
Gate ||WireColor=White
Unknown (Connects to 0/Ground in 6'024'0 circuit) ||WireColor=Red

A picture of the wires coming off the big SCR's. (http://kai.caltech.edu/MotiveDynoController/60240_Removal/images/image/IMG_2462.JPG)

The red wire with unknown purpose connects to the K terminal for each of the three little SCR's on the 6'024'0 Circuit (http://kai.caltech.edu/MotiveDynoController/09_01_08-60240_Schematic-v2.0.jpg) (jpeg).

The Sicon box will need to be switched on in order for the computer controller to work. The K terminal connects to the Sicon ground, which I believe is a positive ground, and so will be "live" whenever the computer equipment controls the SCR's. I don't understand what the red wire does for the big SCR's though. I found a datasheet for the big SCR's, but it doesn't describe the wire inputs.

Westcode Semiconductors
"Convertor Grade Stud-Base Thyristor Type N023R"
PDF Datasheet - N023RH12.pdf (http://kai.caltech.edu/MotiveDynoController/N023RH12.pdf)

If it's a reference voltage for the gate signal, then won't I need to use a separate reference voltage from the BAP-1950 board when using computer control? Any ideas what purpose the red wire serves?

el bob
01-17-2009, 04:26 PM
I took another look at the original Sicon Eddy Current Dynamometer Controller schematic (http://kai.caltech.edu/MotiveDynoController/09_01_04-1348-FullStitch-Cropped.jpg). Each K terminal on the 6'024'0 circuit connects to one of the three big SCR's cathodes, via its respective red wire. This should provide a clean method of "tapping into" the big SCR's and installing a switch between the manual and computer controls.

All three cathodes of the big SCR's connect together and to 0/Ground, before passing through a 0.03Ohm resistor and finally through the brake coil. I would think this means that the three cathode reference connects required by the BAP-1950 would see the same signal.

The example diagrams I have seen so far show how SCR's connect to a three-phase motor where the individual three-phase lines are kept separate all the way into the motor. I have not seen the inside of a three-phase electric motor. Do the SCR cathode output wires come together inside here as well?

01-17-2009, 05:41 PM
I am going to have to get back on this in a bit. We have a lot going on today, and I am quite busy, so I can't spend the time on this that i would like. Your analysis looks good, though.

The brake circuit is all in the secondary of the Z section of the step down (and isolation) transformer. The K terminals are to each SCR's cathode, and electrically common to one another and the reference ground. That is the voltage reference the controller will need to use for the switching, which will amount to sending a positive voltage to each G, or gate terminal to put individual SCR's into conduction.

el bob
01-18-2009, 02:35 AM
I started editing a modified version of the original Sicon eddy current dyno controller schematic. The new version shows which lines are being tapped into and how connectors will be used.

09_01_17-SecondController.jpg (http://kai.caltech.edu/MotiveDynoController/09_01_17-SecondController.jpg)

I am working on a switch mechanism for the dyno operator to toggle between manual and computer control. I originally planned to use a 6PDT mechanical switch, but I am not finding anything suitable on Google, Digi-Key or Mouser. Most of the results for "6PDT" are through-hole, low amperage (~0.7A) slide switches.

01-18-2009, 03:50 AM
One switch and two three pole double throw octal socket relays?

el bob
01-18-2009, 09:49 PM
That seems like a good way to do it. I tried to draw up what I think you have in mind.

This is the beginning of the schematic for the new computer control circuitry. Right now it only includes the computer and manual control switching portion.

Computer Control Circuitry, including Computer & Manual Control Switch) (http://kai.caltech.edu/MotiveDynoController/09_01_17-NewDynoControlBoard.JPG)

I'm looking at Omron relays and a lighted toggle switch for control.

Omron MK3-P5S-AC120 3PDT 120V AC Relay (http://www.grainger.com/Grainger/items/2W922)

Illuminating Rocker Switch (http://www.grainger.com/Grainger/items/2VLR7)

The rocker switch has three pins. I have not used an illuminating 120VAC switch before and am not sure how the third pin is used to light the switch. I have not yet found a datasheet. Somehow closing the switch mechanically results in power passing through its internal light bulb. I don't know why the third pin is needed. Any ideas?

01-18-2009, 11:44 PM
Can't find that mf'r online, but here's a link to an illuminated rocker by Cherrry - http://www.cherrycorp.com/english/rockers/lr_rocker.htm. Get the pdf for how the neon gets lit.

el bob
01-19-2009, 04:08 PM
Thanks beenthere. I put in the order for the switches, relays, sockets, connectors and cable. I tried to find a large illuminated rocker switch. The Cherry TRG series is a small bit larger. I ordered four (minimum order quantity) of the TRG22F5BBRLN (http://www.cherrycorp.com/english/rockers/tr_rocker.htm) switch. I looked to find a version with "ON - OFF" labeling but did not hit much luck. I took a look at the PDF and the lighting mechanism makes more sense now.

el bob
01-19-2009, 04:19 PM
Example "Half Control" setup with the BAP1950 SCR firing board. (http://kai.caltech.edu/MotiveDynoController/BAP1950-HalfControl_Example.JPG) The three diodes that reconnect the three-phase lines to the source after passing through the load, don't appear in the original Sicon eddy current controller schematic. Perhaps they are included in the three over-lapping circles on the Sicon schematic, but aren't drawn in. Are they necessary?

01-19-2009, 05:33 PM
There is a certain amount of uncertainty in the operation of the original. The lines T3, S3 & R4 might be used for phasing reference. But you also have a transformer section Y that feeds another transformer through RL, SL & TL. That transformer, labelled 34 volts, sends lines Rb, Sb & Tb over to the main controller board.

The circuitry in the 0'046'0 board may very well use the Rb, etc lines to track phasing.

The diodes shown in the example with the BAP1950 may need to be added. They are in series with the SCR's, and will have no effect on operation. You might want yet another octal relay to isolate those lines when not in use.

Again, I'm dodging bullets. I have a piece of equipment that I am trying to modify and get sent back this afternoon. If the term 'kludge' hadn't existed until now, I would have to invent it to cover what I am pulling off.

I will do some hunting for a good diode to think about using. Something like a 1N1189 might do, but the diodes would need to match the SCR's ratings. Do you have a number on them?

el bob
01-19-2009, 06:16 PM
I hope all goes well in your kludge'pedition. Dodging bullets can be a demanding task.

I'm not sure if you are looking for a characteristic of the SCR's or just a part number. The part number they are labeled with is N023RH12. Then there's the small logo and another bit of text "B020."

Westcode Semiconductors
"Convertor Grade Stud-Base Thyristor Type N023R"
PDF Datasheet - N023RH12.pdf (http://kai.caltech.edu/MotiveDynoController/N023RH12.pdf)

Regarding the BAP1950's J5 connector and its three-phase references lines, the lines should be disconnected from the brake circuit when the BAP1950 is not live and in control of the SCR's?

Are the three lower diodes installed to work as quenching diodes, like would be used in an automotive relay setup? (Possibly called a suppression diode)

I ordered the BAP1950 and the NI USB-6211. The BAP1950 will take four weeks to arrive. The DAQ should be here within five business days.

01-19-2009, 07:00 PM
They are good for 1500 volts and 48 amps. I will see about finding some diodes to match the current, but at 600 volts.

Probably a good idea to disconnect those lines when the BAP1950 isn't controlling.

Without some info on the functioning of the BAP1950, I'm not certain why they want them there.

You may need a box to hold the diodes plus the relays. The diodes will need to be mounted on heat sinks - they will be stud mount devices. I'll get you some details. The sinks will be about 4 x 2 inches, and stand another 2" high.

Still having fun - this is a prototype unit, and it isn't really all that functional. What I get for a low quote.

01-19-2009, 07:56 PM
Well, that was fun. Vishay makes rectifiers big enough to do the job. Their 70HF(R) series are DO-5 stud mount units. Digi-Key has them as part # 70HFR80 @ $12.10.

I think one heat sink also from Digi will mount them. That's part # 345-1050 @ $19.33. The flat channel is 5.4" long, so it should hold all three diodes. You'll also need 6 pieces of #BER105 insulating washer @ $.88 (or 10/$.79).

The fun part is insulating the studs passing through the sink. I can't find mounting kits anymore - they used to have mica washers plus a teflon insulator that fit over the threads so the stud didn't short to the heat sink. Or you could get teflon washers to stand the heak sink off with so you could just thread the mounting hols for the diode.

Anyway, be careful to meter the diodes to insure they are all insulated from the heat sink, or lots of factory smoke will come out. And we thought this would be easy...

el bob
01-20-2009, 01:36 AM
I updated the NewDynoControlBoard schematic to include a 3PST relay inline with the three-phase monitoring lines connected to J5 on the BAP1950.

Jan. 19 NewDynoBoard Schematic (http://kai.caltech.edu/MotiveDynoController/09_01_19-NewDynoControlBoard.JPG) (jpeg)

I checked out the 70HF diodes on DigiKey. They look serious. The heatsink looks good too. Regarding factory smoke, iIn a relatively high vibration environment, won't the diode studs move within the center of their holes in the heatsink? Some of the big diesels really shake the place. The insulating washers would take care of the top and bottom, but the threads in the middle are exposed like you mentioned.

When faced with a similar decision with mounting the big SCR's, the Sicon techs chose to electrically connect the SCR's to the heatsinks and insulate the heatsinks from the case. The closest thing I could find to an insulated stand-off on Google was a piece from RadioShack (http://www.radioshack.com/product/index.jsp?productId=2102860). On the other hand, what worked for them in that particular situation may not be the most practical approach now. If the stud and nut are tightened down well, they're might not be any problems.

A picture of the insulated standoffs in the original eddy current controller box. (http://kai.caltech.edu/MotiveDynoController/InsulatedStandoffs.jpg)

01-20-2009, 01:59 AM
Yeah, those are really gnarly. The kind of heat sink I suggested mounts nicely with those no-longer-available teflon washers. And it is so nice to just tap in the diode and the screw to attach the wire terminal.

Well, a trip through the old Newark Electronics (sort of like McMaster-Carr for electronics) found part #09WX0134. Those are mounting kits for DO-5 stud mount diodes that include the insulating sleeve to keep the threads off the hole through the heat sink. All of $0.26/ea.

Otherwise, look up the drawing for a Wakefield sink and get grommets (Newark page 2093) to fit. They have enough heat sinks to cross your eyes, too.

el bob
01-20-2009, 08:30 PM
I'm trying to get a better understanding of the purpose of the three regular rectifiers. This is what I have found on Google so far.

Semi-Controlled Rectifier Circuits (http://www.powerdesigners.com/InfoWeb/resources/pe_html/ch06s2/circuit.html)

el bob
01-20-2009, 08:31 PM
Control and Power Electronics Java Applets (http://www.educypedia.be/electronics/javapower.htm)

el bob
01-23-2009, 02:28 AM
I drew up a schematic showing how the BAP1950 SCR Firing Board will connect to the main portion of the eddy current brake coil circuit.

January 22nd, 2009 - Brake Coil Circuit Schematic (http://kai.caltech.edu/MotiveDynoController/BrakeCoilCircuit/09_01_22-BrakeCoilCircuit-800px.jpg)

I tried this one in LTSpice after doing the last few in Photoshop. What a difference. Creating custom symbols is nice and straightforward.

The above link shows the circuit as it appears on the original Sicon Eddy Current Dyno Controller schematic. The next link shows a different version of the simplified schematic that incorporates the "bottom half" diodes called for in the BAP1950 example diagram.

January 22nd, 2009 - Brake Coil Circuit *With Diodes* Schematic (http://kai.caltech.edu/MotiveDynoController/BrakeCoilCircuit/09_01_22-BrakeCoilCircuit-WithDiodes-800px.jpg)

Is there any way to know for sure if adding the diodes is necessary? Then the second part, is there any recommend approach to determining what the effect of adding the diodes on the existing manual control circuitry will be?

I'm going to try emailing the Applied Power Systems engineering staff to get their input as well. I won't hold my breath for a response.

01-23-2009, 02:37 AM
In the first appearance, I thought the added diodes were on the other side of the brake, with their cathodes connected to the SCR's anodes. It would be good to determine which arrangement is correct.

Beats me if the manual control will even notice if they are there. I think it may use the 38 volt transformer as the phasing reference. I still have no idea how it sets firing angle for the SCR's. I suppose you can always place them in circuit and see what, if anything, happens. Do that before wiring in the new controller.

APS should be able to give you a rational reason for the diode addition.

el bob
01-23-2009, 12:07 PM
I took another look at the half control example diagram from the APS BAP 1950 manual. (http://kai.caltech.edu/MotiveDynoController/BAP1950-HalfControl_Example.JPG) It looks like the new diodes are in the right place. What I may have to change are the connections for J5. The example diagram shows them tapping into the circuit closer to the three-phase source, not in-between the diodes and and SCR's.

The sites linked a couple posts above mentioned that the "bottom half" diodes counteract a bit of hysteresis caused by the inductive load. That's probably a poor, possibly inaccurate description on my part, but I don't know exactly what to call it.

Is it possible there are similar diodes located inside the multi-phase converter? I can take a look at it tomorrow, but I figured I would ask in case it might be a common occurrence.

el bob
01-23-2009, 12:40 PM
I spoke to Les at Applied Power Systems. He printed out the simplified brake coil circuit schematic (http://kai.caltech.edu/MotiveDynoController/BrakeCoilCircuit/09_01_22-BrakeCoilCircuit-800px.jpg) and is going to look it over. On first glance, he said he saw no reason why it wouldn't work but wanted to take more time to make sure. I asked about the J5 reference lines and he said they're fine the way they're currently drawn in.

The NI USB-6211 showed up yesterday, as did a few of the parts from Mouser. It will still be some time before the BAP1950 is ready. If the schematic proves to not be a problem, there will be time to work on the data acquisition and LabView side of the project.

01-25-2009, 06:18 PM
I ran up a schematic of how I imagine you would use the relays to switch signals.

el bob
01-28-2009, 01:26 AM
Wow, now that's a real schematic. It manages to show all parts of the circuit on one page and in a manner that's easy to understand. Thanks, that helps a lot.

Looking at the schematic, I'm guessing you think it's a bad idea to leave the 380V three-phase reference to the 6'024'0 circuit live when switched to "Computer Control" mode? While it's not a big deal, in terms of difficulty of the real-world change, to cut the 380V reference connection to the BAP1950 when switched to "Manual Control," it's a bit more difficult to do the former. The 3-phase references lines to the 6'024'0 circuit are actually metal studs that physically attach the 6'024'0 circuit board to the three large R, S and T aluminum heatsinks. This picture shows the studs electrically connecting the heatsinks to the 3-phase reference terminals of the 6'024'0 circuit. (http://kai.caltech.edu/MotiveDynoController/60240/images/image/IMG_2405.JPG) Nothing is impossible, but it would require more than traditional rewiring. A non-conducting plastic stud could be used, and a fourth Mil Spec connector could be added to the Sicon box.

Is D1 the not-yet-installed diode that would make the current Sicon eddy current brake coil circuit resemble the example BAP1950 half-control circuit (http://kai.caltech.edu/MotiveDynoController/BAP1950-HalfControl_Example.JPG)?

Les at Applied Power Systems got back to me and said the January 22nd, 2009 - Brake Coil Circuit Schematic (http://kai.caltech.edu/MotiveDynoController/BrakeCoilCircuit/09_01_22-BrakeCoilCircuit-800px.jpg) would work with the BAP1950. He was not a big fan of the January 22nd, 2009 - Brake Coil Circuit *With Diodes* Schematic (http://kai.caltech.edu/MotiveDynoController/BrakeCoilCircuit/09_01_22-BrakeCoilCircuit-WithDiodes-800px.jpg). This surprised me a bit because I designed the second *With Diodes* schematic to more closely mirror the example BAP1950 half-control circuit. Either way, Les said to use the base schematic without diodes so that's most likely what will be done.

Is CB1 is the relay labeled A05 on the original Sicon controller schematic (http://kai.caltech.edu/MotiveDynoController/09_01_04-1348-FullStitch-Cropped.jpg)?

I started adding the new wires and connectors necessary to add switchable computer control to the dyno. The connectors and wires follow the January 17 - Modified Sicon Controller (http://kai.caltech.edu/MotiveDynoController/09_01_17-SecondController.jpg) schematic.

Sicon Controller Box Modifications Part One (http://kai.caltech.edu/MotiveDynoController/MilSpecDay1/)

Sicon Controller Box Modifications Part Two (http://kai.caltech.edu/MotiveDynoController/MilSpecDay2/)

The original plan was to use a tool that electricians use to punch new holes in electrical boxes, but we couldn't borrow one in time. The general purpose three axis mill couldn't fit the Sicon box. We had to get a bit silly. I forgot to ask what the big green machine is normally responsible for.

I'm interested to hear what you think about the 380V reference wires for the 6'024'0 circuit.

01-28-2009, 01:56 AM
In no particular order:

Good, I could not see the point of those added diodes.

Yes, CB1 is part of A05. I may have misinterpreted it as a circuit breaker. I have worked with German and French schematics, but this is my first Italian one.

Why use a slug punch when you have hole saws? No one can hear the chatter over the engines under test.

No, I don't have any problems leaving the 380 volt lines into the old controller in place. I simply switched them with the relay as with the other lines. They can just be switched over to the BAP 1950 as needed through a set of contacts. The BAP 1950 should only use the lines as a phase reference, so light wiring is in order. Check with them, but 16 ga should be way enough.

i should probably think of other intelligent things to comment on, but I have been designing a new PCB and my brain is a bit full. I'll try to look this over again tomorrow.

el bob
02-03-2009, 08:52 PM
Had to work on a separate job last week. Back to work on the dyno starting yesterday. I spoke with Les at Applied Power Systems and the BAP1950 board might be ready as soon as this Friday. There's no guarantee, but it's sooner than expected which is good to hear.

I started planning the new rackmount enclosure that will house both the data acquisition and SCR control parts. It looks like there will be at least seven connections on the back panel. On the front, there is currently only the illuminated rocker switch for selecting manual or computer control.

Data Acquistion
* Load Cell (Force -> Torque)
* Variable Reluctor (RPM)
* USB (PC Connecdtion)

Dynamometer Control
* Manual Input (Manual Controller Output Signals)
* SCR Control (SCR Input Lines)
* 3 Phase Ref (Three-phase References Lines)
* 120 VAC Supply (BAP1950 & Relay Power Supply)

A rackmount case was ordered from Mouser. It's a "BUD Rak-Mount Chassis" that's 5.25" tall and 17" deep, with a solid bottom panel and vented top panel. This is the respective Mouser catalog page. (pdf)
Mouser Stock No.
* 1x 563-RM-14212 (http://www.mouser.com/Search/Refine.aspx?Keyword=563-RM-14212) - Front, Rear and Side Panels
* 1x 563-TBC-14252 (http://www.mouser.com/Search/Refine.aspx?Keyword=563-TBC-14252) - Solid Bottom Panel
* 1x 563-TBC-14262 (http://www.mouser.com/Search/Refine.aspx?Keyword=563-TBC-14262) - Vented Top Panel
* 2x 563-H-9111-B (http://www.mouser.com/Search/Refine.aspx?Keyword=563-H-9111-B) - 4" Front Panel Handles

Aluminum standoffs were also ordered to mount the BAP1950 0.75" off the base of the rackmount case. The BAP1950 mounting holes are 0.171" in diameter and so should fit 8-32 screws. I checked with Les and the holes in the circuit board are insulated from the rest of the circuitry. The grounds and other traces supposedly do not come near. If the head of the 8-32 screw proves too wide, 6-32's and new standoffs can be used.

Also order Tyco AMP Mate-N-Lok connectors for the connections to the BAP1950 board. J3 is a 12 pin Mate-N-Lok, and J4 and J5 are 5 pin Mate-N-Lok's.

There are going to be a lot of different wires in the enclosure. Any recommendations on an effective labeling system?

02-03-2009, 09:37 PM
We always used peel-off wire markers, but they fall off with time. India ink on a white sleeve under clear shrink-fit would be good.

el bob
02-05-2009, 07:27 PM
Ah, that's a good idea. I'll have to pick up a bit more clear shrinkwrap.

I spent a bit of time on Google looking at what's used commercially and I found that just a label printing machine itself costs around $700. Then there's the label supplies, ink and other parts that probably bring the total around one thousand. If I were going to make lots of these, it might make sense, but not for a one-off.

I realized last night that I hadn't ordered a 3PST relay for the BAP1950 3-Phase Reference connection. I checked the Omron MK Series white paper and they don't seem to have a plain 3PST relay. I have three MK3P5-S relays. Can I use a 3PDT relay as a 3PST relay by not connecting anything to the "Normally Closed" terminals? It seems straightforward and likely to work, but I've made simpler incorrect assumptions before. Should that be okay?

02-05-2009, 07:37 PM
If the contacts are good for the voltage and current, there should be no problem. Your controller shouldn't draw much at all.

el bob
02-06-2009, 12:32 PM
Thanks, I forgot to check the voltage capacity. I'm lucky you mentioned it because the MK relay's voltage rating is indeed insufficient.

General Purpose Relay MK
Max. operating current 10 A
Max. operating voltage 250 VAC, 250 VDC

Now to look for a 3PST relay with a higher voltage rating.

el bob
02-06-2009, 02:20 PM
At first, it looked like the inexpensive and abundant, off-the-shelf industrial relays only ran up to 220-240VAC. I found a few Hartman relays that handle 380VAC, but they were $3,000-$7,000+ pieces designed for aerospace applications. Unless the next Mars rover sports a CAT 3116, I think we are going to have to pass on that one.

Hartman B-312CS, 100A @ 380VAC Contact Rating (http://relays.tycoelectronics.com/datasheets/b312cs.pdf)

I started digging through Google searches for a "380VAC relay" and found another relay product line from Omron. The "General Purpose Plug-In Relay, MJN Series" fits the bill.

Push-to-operate button & LED indicator

Omron MJN3C-AC120 3PDT Relay (http://www.mouser.com/Search/Refine.aspx?Keyword=653-MJN3C-AC1)
UL and CSA recognition as motor controllers through 600 VAC.10 amp @ 28 VDC and 120/240 VAC at 80% pf, 1/3 hp @ 120 VAC, 1/2 hp @ 277/240/480/600 VAC
36 LRA--8.5FLA at 18 VDC, 3 amp @ 480/600 VAC at 80% pf, 10 amp @ 277 VAC resistiveIt's great to find another Omron relay since the other two relays are Omron pieces, but also because Omron provides CAD drawings for their relays.

There's the MJN socket also.

Omron PTF11PC MJN Series Plug-In Relay Socket (http://octopart.com/rtrack?url=http%3A%2F%2Fwww.mouser.com%2Fsearch%2F refine.aspx%3FNtt%3D653-PTF11PC&clicktype=vendorpart_clickthrough&company_id=2401&origin_page=infopage&vendor_number=653-PTF11PC&sid=4838&vpid=2481443&link_type=hyperlink)

el bob
02-06-2009, 02:59 PM
I accidentally picked the wrong MJN relay. They come in a flange mount form and a non-flange mount form. The latter is what can plug into a normal plastic socket. Luckily, I stumbled into noticing this before placing an order.

The non-flange mount part number is MJN3C-IN-AC120. Mouser doesn't stock them, so I found them at onlinecomponents.com through Google.

MJN3C-IN-AC120 3PDT Relay @ OnlineComponents (http://www.onlinecomponents.com/product/2204986)

PTF11PC MJN Plug-In Relay Socket @ OnlineComponents (http://www.onlinecomponents.com/product/2066811)

el bob
02-13-2009, 02:40 PM
Just a quick update. The case and other parts arrived last Friday. CAD drawings were put together and the panels were run on the mill to make all the necessary parts and brackets mounting holes. Once the case was re-assembled and the relays, BAP1950 and USB-6211 were laid out, we realized we were going to also need a precise collection of fasteners. I initially thought we would be able to get away with scrounging in the parts bin. McMaster-Carr delivered the necessary screws and nuts this week, and everything is now bolted together.

I sent an email to Les @ Applied Power Systems, this time asking whether or not the MJN relay inline with the 3Phase Ref wires to the BAP1950 was necessary. I supplied the separate Modified Sicon Controller Schematic (http://kai.caltech.edu/MotiveDynoController/09_01_17-SecondController.jpg) and "NewDynoControlBoard" Schematic (http://kai.caltech.edu/MotiveDynoController/09_01_19-NewDynoControlBoard.JPG). Les asked for a complete schematic on one piece of paper. I had been meaning to do this, but this was the kick-start to get it done.

Three-Phase Eddy Current Dyno Circuit with Dual SCR Controllers (pdf) (http://kai.caltech.edu/MotiveDynoController/09_02_10-DualControllers-v2-with120Vac.pdf)

There's a lot of assembly work to do now, and a little bit of CAD work left. Then it's software design and testing.

02-13-2009, 03:45 PM
The details will always eat up more time than you can imagine. Hope the critter works right the first time.

You might want to add terminal labels to all your control lines for assembly and later reference. I've worked with all white wires and no labels - gets a bit tedious verifying all start and end points. Lots of emergency masking tape labels.

el bob
02-17-2009, 02:58 PM
Thanks for the warning. The potential headache of tracing thirty white wires in close quarters started to weigh on me. I wanted a shrink wrap label printer, but my first search turned up options beginning at $1,000 USD. I took another look on Google this morning and found the K-Sun LabelShop 2012XLST Shrink Label and Wrap Label thermal printer for $400 MSRP. I spoke with Bill @ WireMarkerPlus.com through a nifty online chat window. It's more expensive than writing on tape under clear shrink wrap, but it should get the job done.

I realized on Friday night that the MK relays will not work for switching the six SCR Gate and Cathode signals. The cathode signals are pushing 380VAC and the MK relays are rated to only 250V. This is the reason we spec'ed a different relay, the MJN series 3PDT piece, on the 3Phase Ref connections. The good news is that the same MJN series relay, the MJN3CIN-AC120, can be used for all three relay requirements.

This weekend I aimed to begin bench testing the DAQ side of the new controller. The two input data signals are the variable reluctor (VR) waveform representing engine/dyno RPM and the 3mV/V output signal from the load cell. The VR signal is being passed into a LM1815 circuit in Jean Belanger's Dual VR Conditioner Board v1.1 (http://jbperf.com/dual_VR/index.html). The Dual VR Board outputs a digital pulse train that I previously planned to enter into one of the NI USB-6211's Digital Input channels. After reading sections of the USB-6211 User Manual, I found out I need to connect it to a Counter/Timer type digital input channel. The unconditioned load cell output signal is connected to an Omega OM5 Full Bridge Strain Gage signal conditioner module. The scaled 0-5VDC output signal is connected to an analog input on the USB-6211.

Short of using an actual VR sensor held closely to a trigger wheel being spun by an electric drill, the MegaSquirt Stimulator v2.0 (http://www.megamanual.com/v22manual/v1stim.htm) was the only immediate option for bench-testing the DAQ connections. It uses an IC1 555 pulse timer and a few other pieces to generate a VR-like waveform. Jean helped set up the Dual VR Board, and modify the Stimulator VR output signal, over email on Sunday night. I put together an "instant VI" LabVIEW application that read the frequency of the Dual VR Board's generated pulse train. Yesterday, we were able to vary the RPM reading in LabVIEW my adjusting the RPM control knobs on the Stimulator. This theoretically means that the RPM data input functionality is ready for real, off-the-bench testing. Realistically, in the next week, more time will be spent developing the LabVIEW VI and bench testing.

02-17-2009, 03:15 PM
Probably a good catch on the relay contact ratings. It may make no practical difference, as those lines should not be pulling current so there won't be arcs to break. But it's always a good idea to have proper ratings on everything.

Yes, for RPM, you want to count pulses per unit of time.

Long ago, I worked with a couple other guys to locate a bad wire in a computer. Many thousands of identical white insulated wires running here and there. We used a broom handle, a screwdriver handle, and finally a crochet hook to locate the bad wire. It took three hours to make the fix. Gotta have labels.

el bob
02-17-2009, 03:26 PM
Long ago, I worked with a couple other guys to locate a bad wire in a computer. Many thousands of identical white insulated wires running here and there. We used a broom handle, a screwdriver handle, and finally a crochet hook to locate the bad wire. It took three hours to make the fix. Gotta have labels.

I would love to hear this story. Any computer repair that involves a broom handle, screwdriver and crochet hook rates at the top of the charts in my book. :D

02-17-2009, 04:20 PM
Actually, it was pretty simple. Changing out the logic at either end did not produce results. This was a Univac 1206 (Navy designated it a CP-642A). There were 13 chassis inside the main case. The chassis were about 3' by 4'. Each had thousands of edge connectors with something like 20 contacts. A 2" by 3" printed circuit board holding one to three logic functions was in each edge connector.

Each chassis had a row of 8 connectors along the right and left edge for wiring runs to other chassis and the maintenance panel - I think you can find an illo of one of these online. Yeah, here's a link - http://ed-thelen.org/comp-hist/univac-ntds.html.

Anyway, the side connectors were inserted and disconnected with a rack and cam setup to push in and pull out the mating connectors. Everyone carried around a 3/8" driver with a 5/8" socket to undo door latches and to run the chassis connectors in and out.

We had a failure that was intermittent, and was not affected by the end point logic boards. But you could provoke the halt by shaking the computer. This was fun - the beast weighed in a 2200 lbs. But it was mounted on sprung shock absorber mounts.

Finally, we determined that kicking the left side always brought on the fault. So we pulled the left side panel to expose the wiring. Judicious whacking with a broom handle localized the fault to a vertical range of about one foot. Using a screwdriver handle, the area shrank to a couple of square inches. Fingers eliminated some further wiring, and we got a crochet hook to pull individual wires to locate the one with the problem.

The break, or intermittent discontinuity, was away from the side connectors, so we just cut it back toward the terminations and spliced in a new wire. Just another fun problem troubleshot successfully.

That wasn't even the weirdest fix.

el bob
02-17-2009, 06:38 PM
Finally, we determined that kicking the left side always brought on the fault. So we pulled the left side panel to expose the wiring. Judicious whacking with a broom handle localized the fault to a vertical range of about one foot. Using a screwdriver handle, the area shrank to a couple of square inches. Fingers eliminated some further wiring, and we got a crochet hook to pull individual wires to locate the one with the problem.

Hahaha that is great! I laughed out loud when I read the bold'ed part above. I'm going to have to figure out a way to carry a broom handle in the toolbox. I can't even begin to imagine how many wires you are talking about, I got lost in the listing of components and sub-components. The 5/8" socket and cam-driven connectors sound really neat though.

I realized on Saturday that both the VR and strain gage signal conditioners require +5VDC, and that I had not planned for a 5VDC supply. The Omega OM5 full bridge strain gage needs 200mA @ 5VDC. The half of the Dual VR Conditioner Board v1.1 that I am using needs ~5mA @ 5VDC.

I took a look on Mouser for regulated and caged (enclosure) 5V power supplies. The company Mean Well offers a 25W 5V 5A regulated DC power supply for $34 with a relatively small footprint (3.1" x 2.0" x 1.1"), part number RS25-5. Datasheet (http://www.meanwell.com/search/rS-25/default.htm)

If I wanted to use a supply like the RS25-5 with extra capacity for additional 5V load in the future, is there anything I have to worry about if I only hook up 205mA of load to it? I suppose I could add fuses, but I am not familiar with fuses outside of 5A-30A automotive cartridge fuses. Would I want to install a separate fuse for every device pulling 5V power from it?

02-17-2009, 07:22 PM
You would want to use automotive fuses. They are rated to blow clear at low voltages - something that 250 VAC rated fuses are not. The little supply sounds like it might be a good move. The 5 amp capability means lots of 200 ma loads can be added in the future. The price is pretty good.

As to a separate fuse per load - that is probably going to be awfully busy. See if you can find some value like 1/2 amp, and fuse branches based on that. Just cluster loads so the draw is less than the fusing. Automotive fuses may be hard to find at values less than 5 amps, though. The number of critical 5 volt circuits running unfused is just about equal to the total number of critical 5 volt circuits. We always assumed that a transistor would fail in such a way as to protect the fuse.

If your new control panel has a sense input for it, you might arrange for it to monitor +5 out at an important sensor so it can shut down the dyno if something goes dark.

Note as to fault-localizing technique above - if you can't do something in a way that would worry the people nominally in charge, why bother fixing problems?

el bob
02-17-2009, 08:45 PM
I placed the order for the RS-25-5, a couple of 1Amp ATO size automotive blade fuses, and two inline wire-terminated fuse holders. Fuse holders with bolt holes or other mounting provisions would be ideal, but there didn't seem to be any available for automotive style fuses. Not a big problem.

1A ATO Automotive Blade Fuse (http://www.mouser.com/Search/ProductDetail.aspx?R=142.6185.4102virtualkey576100 00virtualkey576-142.6185.4102)

ATO Size, Wire-terminated Blade Fuse Holder (http://www.mouser.com/Search/ProductDetail.aspx?R=0FHA0001Zvirtualkey57610000vi rtualkey576-0FHA0001Z)

Mean Well 25W 5VDC 5A Switching Power Supply (http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMu0oxGuRuNKHyR6%252 bRRfgR3qayIk46QST7w%3d)

One part of the new controller that I have not begun to think about yet is the 120VAC wiring inside the aluminum case that houses all of these parts. I have seen three individual ~16awg, stranded core wires loosely run inside boxes to care 120VAC and I have seen home construction type Romex cable used. Any recommendations? I'll try and post a drawing of the 120VAC wire routing that's needed.

02-17-2009, 08:51 PM
The 16 ga off a terminal strip is going to work just fine. Use standard colors and just route neatly.

el bob
03-04-2009, 02:37 AM
Just a quick picture before a full update.


03-04-2009, 12:23 PM
Very sanitary layout and wiring. Those Amphenol military connectors are the best (expensive critters, though).

It's so neat, it just has to work.

el bob
03-27-2009, 06:06 PM
The hardware has not been touched much recently. A 5VDC supply was added for the variable reluctor and strain gauge signal conditioners, and two switches were added to the front panel. This is largely good news though because it reflects the fact that the hardware has been working nicely.

Progress is being made on the software side, but like all projects, the details are really showing their teeth. We did have a chance for a very basic, preliminary test last week to use a closed loop PID controller to regulate the dyno's brake and bring the operating RPM of a diesel down from ~970RPM to ~910 RPM.

3/21/09 Engine RPM versus Control Output Signal Chart (http://kai.caltech.edu/MotiveDynoController/LabVIEW/09_03_21-TestingLog02_04-Chart.jpg)

3/21/09 LabVIEW Screenshot (http://kai.caltech.edu/MotiveDynoController/LabVIEW/09_03_21-PID_Testing_001K_EngineKicked.JPG)

I'll post a few pics once the new switches are wired in.

The software development thread is over at the National Instruments discussion board. Here's a a link. (http://forums.ni.com/ni/board/message?board.id=170&thread.id=389025)

03-27-2009, 07:50 PM
The details always eat you alive - but then the hardware is working correctly. Should be interesting to be able to program up a full test cycle.