# Home Brew Controller Combines 2XCurtis 1204s



## jsodemann (Oct 19, 2008)

I have spent the winter putting together a home brew controller based on combining two Curtis 1204s. The 1204s were low cost ebay purchases. The only parts used from the two contollers were the PC boards from the power sections, the copper contact bars, the aluminum heat sinks and one of the PWM signal generating boards.
The first step was to dismantle the two controllers. Once apart all of the FETs and capacitors were removed from the power boards and replaced with higher voltage/current components. A couple of other modifications were necessary like a voltage regulator circuit to take 144 volts down to 48 volts for powering the PWM signal generating board. The resistor on the KSI input of the PWM board had to be replaced with a 100K ohm to prevent over heating. The power boards for each of the 1204s have space and through holes for 16 MOSFETs but both the units I had did not use all of these spots initially. Because of this the reisistors for the gate inputs of these "missing" MOSFETs were also not present. To use these extra MOSFET locations in my design these 75 ohm resistors needed to be added as well. Fortunately the PC board had locations and holes for these. 
The diodes at the A2 input were removed as these will not used in the EV setup. 
Once the components on both boards were installed and remounted on their heat sinks the two units were combined on an aluminum plate. A case to house the unit was made from 1/4 inch aluminum. An electically insulating gap pad was used to mount the controllers inside the case while providing thermal conductivity. 
The whole project ended up costing me about $500. In order to test the unit I built a 144VDC power supply using an isolation transformer out of a pin ball machine. Therefore I have not tested the unit at high current. The unit works well up to the 144 volts from my power supply. As a load I have tested some small series wound motors as well as used a 100watt light bulb. Further testing will have to await the purchase of my EV motor and batteries. Attached is a picture of the nearly completed unit wired up for testing. A polycarbonate cover will be placed across the front and sealed with caulk after final testing.


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## TheSGC (Nov 15, 2007)

That looks really nice! I thought about Frankensteining a few eBay Curtis's, but ended up with a Kelly instead since I just don't have the time, yet.


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## Tesseract (Sep 27, 2008)

That's some serious hacking you did there, jsodemann!

A few observations/suggestions: 

1. Make sure the new MOSFETs don't have a Qg (total gate charge) that is much higher than the old ones or switching losses will skyrocket.

2. Don't forget to alter the threshold at which current limiting kicks in, or else you won't get any benefit from all your hard work!

3. And speaking of, make sure there is always at least 20-50uH of air-core inductance in series with a resistive load (ie - lights) so the current limiting will have enough time to respond.

4. Keep an eye on the temperature of the electrolytic capacitors, especially if you did not "upgrade" those to ones with higher ripple current ratings (the uF value is almost irrelevant at this frequency... even a few hundred uF will provide enough ripple filtering; it's getting the ESR down that is important).

Oh, welcome to the forum...


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## jsodemann (Oct 19, 2008)

Thanks Tesseract your suggestions are very helpful.
1. I replaced the original MOSFETs (RFP40N10) with 32X FDP61N20. The Qg for the old MPSFETs was 300nC. The Qg for the new MOSFETs is 75nC max so I should be good there.
2. I plan on adjusting the limit current when I can run at higher currents. The power supply I made is 10Amp max. I have provided outside access to the adjustment potentiometers on the PWM control board. Is there some way I can make this adjustment without running higher current? 
3.) You mentioned a 20 - 50 mH coil in series with my load. Is this just for testing or do I need this when installed in my vehicle?
4.) The capacitors are something I've been a little concerned about. Each power board originally contained 14X 1000mf 63V caps in parallel. I needed to replace them with caps of similar dimensions. The ones I used are 220mf 160V. These are the size used in the Curtis 1221 based on info from the schematic I found on line. So I have 28 220mf's on the original power boards. I added 6 more on my 144V to 48V voltage regulator board. I then added a seperate board with 6 extra 220mf capacitors, but it is located at some distance (1 or 2 inches) from the rest of the capacitors/boards. I was planning on mounting a thermocouple inside the unit for testing. From what you've said I should probably afix it to one of the capacitors. The ripple current on the old 1000mf caps was 2770mArms. The new 220 mf caps are 900 mArms, but I've gone from 28 capacitors to 40. What do you think? 

Thanks again you have been a great help.


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## Tesseract (Sep 27, 2008)

jsodemann said:


> Thanks Tesseract your suggestions are very helpful.
> 
> 1. I replaced the original MOSFETs (RFP40N10) with 32X FDP61N20. The Qg for the old MPSFETs was 300nC. The Qg for the new MOSFETs is 75nC max so I should be good there.


Yep, your choice of MOSFET is much better than the original and for, what, a dollar more each from Mouser? Shameful, isn't it? 

That said, I would feel better with a bit more voltage margin if this "FrankenCurtis" will be running on 144V. The much lower gate charge of the new fets being driven by the same value gate resistors will result in them switching approximately _5x faster_. While this is mainly a good thing (lower switching loss) it also greatly exacerbates spikes and ringing from stray inductance. The worst case rise time with the old MOSFETs (300nC and 75Ω) was 1.5uS (that is *very* slow) while the new fets will switch in 300nS (arguably ideal) with the same 75Ω. Since you can't do much about the stray inductance - the pc board design is what it is - you might have to add an RC or RCD snubber across the drain-source of the fet bank, or else *increase* the value of the gate resistor (e.g. to 100Ω) to slow them down. Post a scope shot of the drain-source waveform if you can.




jsodemann said:


> 2. I plan on adjusting the limit current when I can run at higher currents. The power supply I made is 10Amp max. I have provided outside access to the adjustment potentiometers on the PWM control board. Is there some way I can make this adjustment without running higher current?


This is going to be tricky, for sure. In other Curtis controllers (see, for example, the one that Otmar reverse-engineered at the Cafe Electric website - http://cafeelectric.com/curtis/ ) the current is indirectly measured by looking at the voltage drop across the drain-source channel when the fets are on. Unfortunately, on resistance is not well specified, varies incredibly with temperature (a quadratic term involved) and at this low of a resistance level sometimes the soldered connections contribute just as much to the voltage drop. One thing is certain, whatever the current limit was before is not what it is now. 




jsodemann said:


> 3.) You mentioned a 20 - 50 mH coil in series with my load. Is this just for testing or do I need this when installed in my vehicle?


Yikes - 20-50 _micro_henries, not millihenries! You only need this for testing with a resistive load (light bulbs, big blocks of graphite (what I use), etc.) And speaking of resistive loads - you might want to consider using an old space heater with a nichrome "ribbon" as the heating element for a load (more power, less delicate). 




jsodemann said:


> 4.)...So I have 28 220mf's on the original power boards. I added 6 more on my 144V to 48V voltage regulator board. I then added a seperate board with 6 extra 220mf capacitors, but it is located at some distance (1 or 2 inches) from the rest of the capacitors/boards. I was planning on mounting a thermocouple inside the unit for testing. From what you've said I should probably afix it to one of the capacitors. The ripple current on the old 1000mf caps was 2770mArms. The new 220 mf caps are 900 mArms, but I've gone from 28 capacitors to 40. What do you think? ...


Nichicon KXG and Panasonic TS-ED are both good choices here. In general, you are going to find the best combination of ripple current rating at 105C and high voltage with capacitors made for "electronic ballasts". 

Unfortunately, the farther a capacitor gets from the FWD-MOSFETs the less effective it will be at smoothing out the input ripple. So, those closest to the switches/diodes take up a much larger share of the ripple current than expected, heating up more, which raises their ESR, which results in more heating, etc., until they blow up (literally). That is to say, the extra caps you added probably aren't doing a whole lot. They aren't hurting anything, but I suspect their contribution is minimal.

The good news is that as long as you don't allow the ambient temperature to get anywhere close to the maximum stamped on the capacitor (typically 85C or 105C, try to only use the latter in this sort of application) you can pump more ripple current through the capacitor. Another plus is that ripple current is usually specified at 120Hz and goes up with frequency - a 1.5x mulitplier at 10kHz is typical. Caveat: using both multipliers, temp and freq, will result in the capacitor only lasting its "rated" lifetime (e.g. - 2000 hours, 3000 hours, etc.). This would be totally unacceptable in an industrial motor drive that might run 24 hours a day - it would croak in just a few months of operation - but is usually an acceptable trade-off in an EV.


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## jsodemann (Oct 19, 2008)

Tesseract
I am actually planning on running my EV on 120V worth of batteries. My test supply puts out 144V under a lower load (60W bulb) so I've been testing under these conditions. If I load up the controller with two 100W bulbs my power supply puts out 120V max at 1amp through the bulbs. I've added a pictures of my scope placed across the Source/Drain. The first scope picture is running 120V at 1 amp. The second is a 60W bulb as load and was running 140V at 0.35A. As you can see the wave form isn't quite as clean. Neither of these had a 20micro henry coil in series. Replacing the 75 ohm resistors with 100 ohm would be an easy fix. Adding snubbers would be a little more difficult. Based on the waveforms seen do you think either will be necessary?
A note on my capacitors, I am using the 105C rated type. Beyond that I'll have to wait and see what temps I see in testing when I have the motor and batteries.
Otmar's schematic is pretty close to the 1204. I used it extensively in this work. The main difference was the 144V to 48V voltage regulator which I added. The values on some of the componants are also different. I didn't trace every part of the circuit however so there could be some other differences. 

Thank you very much agian for all your advice, it has been a great help and has taught me a lot.


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## Tesseract (Sep 27, 2008)

jsodemann said:


> I am actually planning on running my EV on 120V worth of batteries.


Ah, okay. 200V fets should be fine, then.




jsodemann said:


> My test supply puts out 144V under a lower load (60W bulb) so I've been testing under these conditions. If I load up the controller with two 100W bulbs my power supply puts out 120V max at 1amp through the bulbs.


Keep in mind that a motor controller reduces average input current bv the same proportion as it reduces average output voltage. That is, if the PWM duty cycle is 50% and the output current is 10A then the input current is 5A. If the duty cycle is 10% then the input current is 1/10th the output current, etc.If you limit the "throttle" excursion you should be able to draw much higher peak currents that the isolation transformer would otherwise allow (you really need to have at least 10A on the input to get a meaningful amount of current from the output, though). Which leads to...




jsodemann said:


> I've added a pictures of my scope placed across the Source/Drain.... Based on the waveforms seen do you think either will be necessary?


The first waveform looks textbook perfect... for a resistive load, but you're not switching enough current to excite any stray inductances, hence, no ringing, not overshoot, etc.. 

Oh, and no problem with the help. I'm developing a controller for commercial sale myself but don't mind helping out those who have taken the initiative to whip up something on their own


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## jsodemann (Oct 19, 2008)

Sounds like I either need to build a bigger power supply or wait until I purchase the motor and batteries. The isolation transformer I used was a small unit out of a pin ball machine. It said it was rated for 10A so I sized the bridge rectifier etc for 10A. I haven't been able to pull more than 1 amp at the out put of the controller regardless of where I set the throttle which I guess means I'm not getting anything like 10A from the power supply.

Could I draw more current with a different load, say like an old space heater as you suggested?


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## Tesseract (Sep 27, 2008)

jsodemann said:


> Sounds like I either need to build a bigger power supply or wait until I purchase the motor and batteries. The isolation transformer I used was a small unit out of a pin ball machine. It said it was rated for 10A so I sized the bridge rectifier etc for 10A. I haven't been able to pull more than 1 amp at the out put of the controller regardless of where I set the throttle which I guess means I'm not getting anything like 10A from the power supply.
> 
> Could I draw more current with a different load, say like an old space heater as you suggested?


You don't need a bigger power supply just yet, you need a bigger load. Several halogen bulbs in parallel would be a good next step, or a space heater. But you also need some inductance. Right now you can make the inductance with #10 solid THHN wire (good for 30A continuous at 90C, but will easily tolerate 100A or more for a few seconds). About 20 close-wound turns on a 4" PVC pipe should do (~30uH). 

Keep a very close eye on ringing/overshoot at the beginning of the voltage waveform as that is when the fets are turning *off*. Ringing will increase with output current and is proportional to the stray inductance of the internal circuit (has nothing to do with the external inductance which you need to slow the current rise time down and make your load look more like a motor).

Good luck, and don't forget your safety glasses...


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## jsodemann (Oct 19, 2008)

Well this is what I was able to put together with what I found in my workshop. I found a coil in my junk box made from what looks like 14 gauge magnet wire wound into a 10 inch coil of between 250 to 300 turns. I put this in series with my halogen spot light and two 100W bulbs. At the output of the controller I was getting 3A. The voltage was 102V. The wave form still looks pretty good. (see attached) I will have to look for a better load or maybe get another halogen. I have also attached a pictureof the 10 inch coil next to the controller and halogen.


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