Eddy Current Retarder Help

shortbus

Joined Sep 30, 2009
10,045
If this is for a shop, why not just invest in the original manufacturers replacement console/controller? Telma is still alive and well. A DIY controller is just going to risk destroying your retarder.
 

LowQCab

Joined Nov 6, 2012
4,023
"" why not just invest in the original manufacturers replacement console/controller? ""

Because it's crude and outdated.
Of course they may have up-dated their Controls, I haven't looked ...........
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shortbus

Joined Sep 30, 2009
10,045
Of course they may have up-dated their Controls, I haven't looked
Not surprising. The controller that fried looks to be a brake type controller they are on or off nothing in between. They are used when the vehicle is already stopped, if you want them to last anyhow.

He needs to up grade to a real dyno controller that will do everything like a real dyno does, including communicate with a computer for real time read outs and step out puts like a dyno. The only thing is Telma's dyno control might not work with the truck retarder model he has.

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MisterBill2

Joined Jan 23, 2018
18,171
The organization that own it is not a shop: It is a race-car driver club, as stated in post #1. Probably not a high-budget group, or they would just rush out and buy a current technology dyno system for a whole lot of money.
"An entire club of race car drivers would sincerely appreciate your help.
BTW we are only driving 1 coil on the retarder. "
So now that the scheme for using a PWM signal rather directly to control the retarder current, the challenge will be to find a means to handle the details of the described replacement. Which would not be hard for an experienced electronics tech person, but a serious challenge for somebody who has not built any power electronics yet.
 

Thread Starter

Rocketman12

Joined Apr 20, 2022
13
Thanks MisterBill2,
You are correct. Very low budget racing. Formula Vee. Only 70Hp. We don't charge anyone for using it. We just try to help each other out.
Currently we haven't dismantled the retarder at all. The fan on it works fine. It does however only have the 2 cables (Black and Red) coming from it and travelling through the wiring harness down to the control box end. Just to add a little more info - Attached is a pic of the transformer when I had it out. I have labelled 2 testpoints. I was getting 80v AC between these points.
 

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LowQCab

Joined Nov 6, 2012
4,023
To determine what's actually going on with that Transformer
might require an In-Person inspection and testing,
unless someone on-site has experience with Transformers and the use of a Multi-Meter.

Have You contacted the manufacturer to see if they can supply You with a complete Schematic ?

It "looks-like" the 2 Terminals at the top of the picture are probably the
connections for the Secondary-Winding.

The Picture doesn't show what the single bottom Terminal is connected to,
( maybe a Secondary-Center-Tap ?, Ground maybe ? ).

The lighter colored Coils are "probably" the Primary ( 120/240-Volt ), Windings,
and would have much smaller Wires connected to them.

If the intention is to use the Transformer as a "Choke", as I suggested in my Schematic earlier,
only the Secondary-Winding would be used, ( the 2 top terminals with heavy Wiring ),
and any connections/Wires to the Primary-Windings would definitely not have any value,
or be needed or used for any other purpose.
Never the less, the Primary-connections would have to be identified,
and substantially insulated from each other, and everything else,
as these connections could have over ~1000-Volts of potential between the Primary-Terminals/Wires.
This will not create a problem,
as long as the proper attention is given to permanently insulating the Primary-connections.

As far as compatibility with other Control-Systems ...........
The Circuit that I suggested earlier has a fairly ubiquitous,
"Logic-Level"-PWM-Input to smoothly control the Retarder from
0 to 130% of it's originally configured Torque-capacity.

The only bugaboo might be the compatibility of the
"combination Tachometer and Torque-Sensing"
arrangement originally used on the Dyno,
with a new type of System which may use different means for collecting that important information.

A simple Micro-Controller could easily be set up to convert these signals into different formats,
just don't ask me to do the programming.

We still don't know what type of Sensors are used on the Interrupter-Wheels,
but there is no shortage of excellent, cheap, replacement Sensors that will generate
nice clean Square-Waves every time one of those holes goes by.

New Interrupter-Wheel Sensor-mounting-bracketry shouldn't be much of an issue,
but at least one of them does need to be made accurately adjustable, and both need to be very ridged.
This will insure the capability of achieving an accurate "zero" positioning relative to the 2 Interrupter-Wheels,
just in case the holes in the 2 Wheels are not perfectly aligned with each other, because of wear or abuse.
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MisterBill2

Joined Jan 23, 2018
18,171
The one post that included links to the manuals provided all of the needed information about connecting to the retarder coils. The connection scheme is very much polarity sensitive, but if the coils are actually coded as described putting all six coils in series will not be difficult.
The transformer in the photo is certainly a high current device, but I saw nothing to tell me if it was to provide 12 volts or 24 volts. But with the PWM scheme proposed the transformer will not be required.

In the series circuit it is the voltages that add, not the currents. And with the single series connection there would be six coils requiring 12 volts each at maximum power, and so for full breaking torque at 100% duty cycle 72 volts would be required. But by using the on/off mode of pulse width control, it is simple to get the same average power from a shorter duty cycle. This is what I was describing in a previous post.
The big benefit now is that the control transistor does not need to control that very high current, and the good news is that the transistor to control the higher voltage will cost much less than the higher current devices.
The other big benefit is that the PWM signal from the controller can be used without needing it to be converted into an SCR control signal.
I am really hoping that this all makes sense to the TS, because it is just a bit past 3:30 AM here. Probably I am repeating myself a bit.
 

Thread Starter

Rocketman12

Joined Apr 20, 2022
13
Well by all means go to bed and look at this whenever you have some free time :) It's been broken for quite some time so more days are not going to hurt.

  1. I think I have an understanding.
  2. We are looking at the Circuit diagram from Post No#14.
  3. We are removing the capacitors as there is no filtering required.
  4. The top right represents the retarder coils and I need to open it up and connect them in series or
  5. Test the input cables to see if it is already in series. (Can I test that with my multi meter?)
  6. Are we still using the secondary winding from the Transformer or did we decide something else?
  7. Can I use the Opto coupled controller I posted before as the Logic Level switch for the 15v?
  8. Any ideas on the values for the Mosfet?
  9. Note I am on 240v as we are in Australia.
  10. Can I build this on a prototyping breadboard or does it carry too much current?

These questions are based on what I think I understand. If the questions don't make sense, then perhaps I don't understand.

LowQCab -the sensors have not been effected. I am running them currently powered from my arduino and can produce speed and torque figures. All of the information that used to come from the old boards is now produced programmatically by the arduino. Essentially everything to do with measurements is working in my new setup. Just need to physically implement the circuit to engage the retarder.

Thanks everyone for your help so far.
 

MisterBill2

Joined Jan 23, 2018
18,171
Oh Wow!! I had forgotten about the 240 volt mains. That will alter the complexion of the power supply arrangement a bit. Even possibly quite a bit.
The transformer may come into play as an important element.
Are you able to power the transformer by itself and measure the output voltage? And, also, does the transformer have an arrangement to be able to connect it for a 120 volt input, (four terminals), or is the primary connection only for 240 volts (two terminals only)? And does the heavy current secondary consist of only one winding, not tapped in the center,(two terminals only), or is it a center-tapped winding intended for a full wave rectifier? (three terminals)?
My previous thinking had been for 120 volt mains, which would be more convenient. The series scheme for the connection and control will still hold, but the power supply circuit becomes more complex and tedious.
 

shortbus

Joined Sep 30, 2009
10,045
And with the single series connection there would be six coils requiring 12 volts each at maximum power, and so for full breaking torque at 100% duty cycle 72 volts would be required.
Are you sure about that? If so where would that high of a voltage come from in a truck that would be either 12V or 24V? After all that is where this came from.

Following most of what is said here I predict smoke
 

MisterBill2

Joined Jan 23, 2018
18,171
Are you sure about that? If so where would that high of a voltage come from in a truck that would be either 12V or 24V? After all that is where this came from.

Following most of what is said here I predict smoke
The intended application for this specific piece of hardware is in a stationary chassis dynomometer application. In addition, the setup manual describes in great detail the arrangement for having three pairs of coils operating on 24volts. with the maximum current draw being in the 43.5 amp area.
Given that this particular setup will be stationary and mains powered, an alternate arrangement with each of the 24 volt pairs in series for a maximum requirement of 72 volts, is a better choice for operation, as only one third of the current will be required.

There will be no trucks involved in this installation for this application.
 

LowQCab

Joined Nov 6, 2012
4,023
Well, I certainly missed a few very important points ...........
I didn't realize that the Software aspect had already been handled.

In that case, it comes down to using a single Rectifier-Diode on the Power-Input to cut the
"Average-Power" in half.

I don't care for the idea of using unfiltered AC- Voltage,
especially when it now needs to be chopped-up even more to compensate for the
above single Diode, ( instead of a Bridge-Rectifier ),
but it's the simplest way to cut the Voltage in half.
And Yes, I know that it will "work", but that doesn't mean it isn't a really crude way to do it.

With no Choke and Filter-Capacitors, this thing is going to be very noisy, and vibrate like hell at 50 or 60hz.
It's probably heavy-duty enough that it won't actually hurt anything,
but no Filtering certainly can't be called "refined" in any way.
And, there's a possibility that the vibration created could easily create a tremendous amount of
noise on the "RPM / Torque-Signal" from the Interrupter-Wheels.
Smooth and quiet is better.

I missed the suggested Circuit-Board earlier in the Post,
if this is what is still in question, then no, that Board is not appropriate for anything in this project.

What is needed is a small Isolated-Switch-Mode-Power-Supply-Module,
with a Regulated-Output of 12 or 15-Volts DC,
and a proper Isolated-Input-FET-Driver-Chip with enough grunt-Power to
cleanly switch a High-Power MOSFET without generating too much Heat,
neither of which has been decided upon just yet.

With 240-Volts AC being the minimum Mains-Voltage available, I would say figuring-out the
existing Transformer is the first line of business.
If that Transformer can turn 240V into ~80-Volts AC, that would be pretty close to ideal.

A lower Output-Voltage from the Transformer can still be worked with,
but the Transformer is an unknown, and required, item at this point.

The Secondary-Winding appears to be obvious,
( although it may have a "Center-Tap" which is not needed ),
but the Primary-Winding(s) are in question, ( at least they are for me ).
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MisterBill2

Joined Jan 23, 2018
18,171
What we do know about the transformer is that it ultimately supplied either 12 volts or 24 volts to the eddy current braking unit with a maximum of, I think, either 70+ amps or 40+ amps. This may have been a constant duty rated output, as well.
If the transformer has a split primary then perhaps it could be used as a step-down autotransformer, with the secondary connected to subtract voltage so that the output might be down 100 volts or so. The thing being that the current into the brake magnets still needs to average up to about 25 amps for maximum braking. At lower levels of braking with shorter duty cycles the current will be less because the large inductance will limit the current rise, and the shunt diode will allow current to continue flowing as the magnetic field collapses. It is that collapsing magnetic field produced current that was making me think that less filtering will be needed. This is a very interesting application because the load is very inductive.
 

shortbus

Joined Sep 30, 2009
10,045
The intended application for this specific piece of hardware is in a stationary chassis dynomometer application. In addition, the setup manual describes in great detail the arrangement for having three pairs of coils operating on 24volts. with the maximum current draw being in the 43.5 amp area.
Given that this particular setup will be stationary and mains powered, an alternate arrangement with each of the 24 volt pairs in series for a maximum requirement of 72 volts, is a better choice for operation, as only one third of the current will be required.

There will be no trucks involved in this installation for this application.
Just to bad that following your advice in this can't be followed by a law suit! Truck or not the original retarder was powered by a single 12 or 24 volt system, and all coils were used at one time, powered by that system.

Not throwing stones, just stating facts that if you would go to the Telma sites you would see too. Another of those threads where you agree with the TS and lead them down the "primrose path".
 

shortbus

Joined Sep 30, 2009
10,045
There can be no understanding by those unable to see the difference between a parallel circuit and a series circuit.
If you take the time to look at the PDF the TS gave the only difference between the 12V and 24V models is the way the coils are wired, 12V is parlell and 24V is series. But thats said, each pole/coil pair is SWITCHED on separately, you choose the number of coils needed 1-3 to apply the needed drag. Running those coils from 80V is not a good idea.
 

MisterBill2

Joined Jan 23, 2018
18,171
The control scheme is to be Pulse Width Modulated. That means a variable duty cycle, from almost nothing up to quite a bit. And if six of the coils that take 12 volts each are put in series then the voltage for 100% is 72 volts. But as the magnetic field is a function of the effective power, the power can be varied by adjusting the on time. And the power will be smoothed by means of the diode across the input, which will allow current to continue flowing when the transistor switches off.
The original crude control scheme was to switch one, two, or three pairs of coils on at full power, which would create three different torque loads. By using the PWM scheme the torque can be varied from zero to maximum quite smoothly.
And it looks like the original dyno was created and marketed using an available magnetic retarder. So the dyno application is not new to this thread, it was a dyno before these folks ever owned it.
 

Thread Starter

Rocketman12

Joined Apr 20, 2022
13
So the transformer in question is a little more complicated than I had indicated.
It has 8 terminals. The testpoint pic from earlier was from the top. This pic is from the front.
You see the middle 2 terminals are connected to 240v. The top right is bridged to the bottom right.
The top left feeds to one of the Triac Plates.
The bottom left feeds to the other Triac Plate.

On the back the top terminal goes to the black wire of the retarder. It also connects to the diode on each of the plates.
The bottom terminal goes to the red wire on the retarder. It also goes to the anode on each triac.

The transformer is only used to run the retarder and triac plates. It does not supply power to any other components.

I think I may have to try drawing the circuit. Could take a while as I may have to do some disassembly.
Any thoughts on basic circuit drawing software?
 

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