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  #1  
Old 11-19-2012, 08:49 PM
chay chay is offline
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Default Understanding the MC-60 treadmill motor controller schematic

I'm working to learn how to build my own motor controller for what I envision to be an open source treadmill walking desk.

After playing with a number of arduino circuits and applications, I felt ready to move up in horsepower to treadmill-sized PMDC motor controllers, but found there's not yet much available that I could find by way of tutorials and helpful information for designing circuits at this amperage and voltage.

So I decided to study the motor controller on a used Proform treadmill that I inherited. It uses an MC-60 motor controller. On this forum, I found two relevant mc-60 schematics, one from Tom Rollins ("trolley1"), and the other from "SgtWookie".

Tom Rollins commented with regard to his schematic that it might be missing some resistors, so I thought I'd engage my own learning with his schematic in the background to see if I could reproduce his schematic on Eagle CAD, which I also wanted to learn, by following his reverse-engineering process on my own PCB. I did that, and filled in names and values to devices for which I also downloaded data sheets. I found what I believe were a couple of mis-labeled devices, and a missing trace. I've attached my hopefully improved schematic here, and I blogged about the schematic and my process here.

These are two circuit-level changes from the Rollins' schematic (also attached) to mine. I've more than triple-checked them. I think I've got them correctly.

1) In the attached mc-60v4 schematic (mine) there's a start-up sub-circuit, I believe, centered on U2_A (under the speed control pot) connected through R20 to leg L (Low)(this is only faintly labeled on my schematic, I see). On Tom Rollins' schematic, he shows that to be connected to leg W (Wiper).

2) Between R7 near U2_D (below the LED SCR Trigger) and R9, the trace on my schematic including R10 does not show on Rollins' schematic.

At any rate, now I'm to the point of trying to better understand design elements of the circuit. I have a load of amateur-level questions, but I'll start with just three.

1) I understand how a full bridge rectifier converts AC to DC. The conversion here, as I understand will be pulsed to A+ anywhere from 0-120VDC. I understand how SCRs work. That given, how does 120VDC get stepped down to a steady 12VDC for the rest of the circuit? I see the circuit returns from the rectifier through D5, R14, between D4 and D% and through R9 (5KOhms). This probably is simple, but I've not figured it out for myself yet. Is the zenar diode, D10 key, I wonder?

2) What does D12 do in the rectifier that's helpful? Why is it there?

3) What do D4 and D3 do, and why are they connected to the AC input?

Understanding this would be for me a great start.

If anyone wants a copy of the Eagle CAD file or datasheets, let me know. Thanks in advance.
Attached Images
File Type: jpg mc-60v4.full.jpg (274.7 KB, 216 views)
File Type: jpg mc-60v4.full.subcircuits.jpg (118.2 KB, 183 views)
Attached Files
File Type: pdf MC-60MotorController.TomRollins.pdf (386.5 KB, 227 views)
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  #2  
Old 11-19-2012, 09:35 PM
Jony130 Jony130 is offline
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I just did a quick look at the diagram and yes D10 + R9 "create" 12V for almost all electronics component in the circuit.
http://en.wikipedia.org/wiki/Zener_diode#Uses
Also D4 and D3 (D1 and D2 also) are the rectifier diodes for "Zener voltage regulator".
D12 - I'm not so sure yet, but maybe this diode is to reduce the motor Inductive kick.

Also you have a error in your diagram. Why R16 (1K) resistor is in series with motor? How can this work?
And why this resistor is connect via R13/R13 to SCR gates?

Last edited by Jony130; 11-19-2012 at 09:42 PM.
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  #3  
Old 11-19-2012, 10:09 PM
chay chay is offline
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Default Rectifier, R16, 12V

Thank you Jony130.

Hmm.
With regard to D4 and D3, I see. That is so interesting. I had been assuming that Q2 and Q3 did that. Thank you. So the opto-isolator, U2 is between the two half bridges of the rectifier.

You wrote:
Quote:
Also you have a error in your diagram. Why R16 (1K) resistor is in series with motor? How can this work?
And why this resistor is connect via R13/R13 to SCR gates?
I don't know. But I just pulled out my PCB and put the multimeter to it. There's definitely continuity for R16 between A+ and R12/R13. Check and double check. The PCB was working fine when I pulled it off the treadmill, too.

With regard to getting 12V, now I'm understanding R9 (5K) to drop 120V to 24V and the Zenar diode, D10 just drops any voltage over 12V to ground, right?

Can I ask you about other parts of the circuit, or should I start a new thread to do that?
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  #4  
Old 11-20-2012, 12:27 PM
Jony130 Jony130 is offline
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Quote:
Thank you Jony130.
I don't know. But I just pulled out my PCB and put the multimeter to it. There's definitely continuity for R16 between A+ and R12/R13. Check and double check. The PCB was working fine when I pulled it off the treadmill, too.
I'm 100% sure that this is a error only on the diagram.
It's impassible that a small R16 1K resistor can survive the current that is drown by the motor.

Quote:
With regard to getting 12V, now I'm understanding R9 (5K) to drop 120V to 24V and the Zenar diode, D10 just drops any voltage over 12V to ground, right?
Why R9 drops only from 120 to 24V?? Simply we have 12V across D10.
Quote:
Can I ask you about other parts of the circuit, or should I start a new thread to do that?
You don't need to start another thread. Ask question in this thread
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File Type: jpg a.JPG (26.8 KB, 128 views)
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  #5  
Old 11-21-2012, 12:29 AM
chay chay is offline
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Default mc-60v5 corrected

Thanks again, Jony130. That was really helpful, and in particular, the image you shared was very helpful to me.

I revised the schematic to reflect your insights, I think. Did I get it right? In addition to adding a trace from C17/C18 to the A+ side of R16, I searched for and found a different Eagle CAD schematic representation of the opto-isolator.

The attached schematics are the same, just different scales (800px and 1000px wide).

[Oops. I see that I labeled the SPEED CONTROL POT as 0-120VDC. I know it's actually 0-12VDC. I'll fix that.][Done.]

mc-60v5.800w.jpg

mc-60v5.1000w.jpg

Last edited by chay; 11-21-2012 at 12:46 AM. Reason: New images to attach.
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  #6  
Old 11-21-2012, 02:45 AM
chay chay is offline
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Default Pseudocode-level explanation of sub-circuit?

I don't know if electronics experts regularly do pseudocode, but I wonder if you, Jony130, or anyone else could give me a pseudocode-level explanation of the sub-curcuit in the loop from about U2_C and above?

I've double checked the orientation of D5 on my PCB. The schematic seems right, but that orientation confuses me as I try to decipher that loop in the circuit. Any help there?

Thanks.

mc-60v5.1000w.jpg

Last edited by chay; 11-21-2012 at 02:47 AM. Reason: Add schematic.
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  #7  
Old 11-21-2012, 04:49 PM
Jony130 Jony130 is offline
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Quote:
Originally Posted by chay View Post
I don't know if electronics experts regularly do pseudocode, but I wonder if you, Jony130, or anyone else could give me a pseudocode-level explanation of the sub-curcuit in the loop from about U2_C and above?
Do you mean this part of a circuit (see attach file)



Quote:
Originally Posted by chay View Post
I've double checked the orientation of D5 on my PCB. The schematic seems right, but that orientation confuses me as I try to decipher that loop in the circuit. Any help there?
Sure we can help see this picture
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File Type: png MC-60MotorControler.PNG (48.2 KB, 121 views)
File Type: png 119a.PNG (32.2 KB, 351 views)
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  #8  
Old 11-21-2012, 06:34 PM
chay chay is offline
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Yes! Thank you so much for that picture. I get that part, now. I love it.

Yes, too. If you had energy to give me a pseudo-code-like explanation of of this part of the circuit you provided, that would be wonderful.

I've been studying op-amps in my own attempt to unpack that, but so far I've gotten confused on the feedback around U2C, and combined effects the op-amp chain. U1C also confuses me.

Thanks!

MC-60MotorControler.allAboutCircuits.PNG
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  #9  
Old 11-22-2012, 04:44 PM
Jony130 Jony130 is offline
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As for the op amp try read this "tutorial"
http://forum.allaboutcircuits.com/sh...15&postcount=9
Also I want ask you about R1 resistor and Q4. Are you 100% percent sure that R1 is connect between Q4 base and diode D9 anode? Because in this configuration I don't see how this circuit supposed to work. It seems to me that R1 resistor should be connect between Q4 base and GND and additional Q4 base is connect to D9 anode.

Last edited by Jony130; 11-22-2012 at 04:54 PM.
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  #10  
Old 11-22-2012, 08:37 PM
chay chay is offline
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Default mc-60v6

Holy cripes. You are so right, Jony130. That was screwed up. Jeeze, you're good.

See attached. This is what it looks like to me, now. I double-checked this part of the circuit on the PCB this morning. Does it look right to you? R10 connects the wiper to U2_A(3). R7, C5, and R4 form a loop at U2_D. R1 seems right between Q4 and D9/R9. Man, I don't know how I got that so wrong.

Thanks for the op-amp tutorial link. I'll do some more studying.

mc-60v6.png
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