Paul & Sabrina's cheap DIY 144v motor controller

[JayC]

Originally Posted by blowncurtice

I am trying to cut the cost of the controller for myself, having said that I still want a very good reliable controller, hence I would go for the larger power capacitors in the latest version. I believe that someone on the forum is advocating extruded alloy plates bolted together for the case, this would probably have better heat transfer properties than sheet alloy bent to form a case like the one from Hondo,but I can get an alloy case bent up for no more than $15.00 and another$5.00 for a good base plate, combine this with an alloy heat spreader and I may not have the gold plated version but I think it will serve my purpose. I have a 1985 Camira station wagon,kerb weight with no passengers is 1135Kg, I have a 9" advanced DC motor and drive conservatively I try not to exceed 200amps and most of my driving is highway at about 80KPH this pulls less than 100Amps cruising and is mostly below 50Amps. I will have a case bent up tomorrow and post a photo and a better idea of cost, this may not help our friends in the US as postage would probably be expensive and those of us in Australia may be able to get it made localy cheaper or if they prefer make one from extruded aloy but for those interested this may be an option.
John

Anodizing adds to the heat emissivity of the aluminum. Darker colors (black) are better but any anodize is better than oxide. Also, I'm an EE and thermo was one of the only ME classes I was required to take. I may have my terminology wrong but this is one point that stuck with me. Another thing is it's not mainly the thickness it's the surface area. This is why they cut fins, etc. The more surface area, the more radiant capability.

FWIW,
Jay

[edown]

I just did my first road test of my EV (92 Eagle), about 4 miles. Took it up to 50mph and still had some left.. But kind of slow to get there.. I'm only running 96 volts.. Anyway, my water cooled controller didn't even get warm.. I hit 400+ amps twice.. But my motor got too hot to hold your hand on, guess I will have to add a blower to it.. I was pushing it kind of hard, 150 to 300 amps most of the time.. I decided not to put the controller in its own box, but use one big box for all the goodies, it will have a plexy cover.. The 110 inverter in the PIC runs a .4 amp "little giant" pump in the paint can..

[edown]

Here is a close-up.. I'm still using just a 555 in my control section.. Waiting for Paul's perfected version.. But it works well..

[MPaulHolmes]

You gangster! You are the man!!! Edown, that looks beautiful!

[blowncurtice]

These are two photos of my controller case, A local bent it up for me, the cost $15.00 for the main case and another $5.00 for the end cap which I riveted on. The other end will need to be made of an insulating material. For our Australian Modders I will get a cost of the postage tomorow, however check with your local supplier you may do better. So far the only price I have for the base plate is $22.00 from a Melbourne supplier. Copper bus bar 1/4x3/4x3.6 Meter $ 63.00.
John

[vince]

Edown;be good to know specs on your eagle( web pge/ev album-not sure if you should use this thread)thanks, Vince.

[blowncurtice]

Paul
I know that Don from Brisbane (mcudogs) is taking care of the power board, do you have anyone looking after the logic board.
John

[MPaulHolmes]

Don has been modifying the control section too. We've been talking back and forth, trying to figure out what to add without it growing too unwieldy. I need to get back to him. He had a really good idea about hot to get an rpm sensor on the board.

[jyanof]

Paul suggested we investigate the sources of heat generation in the controller by changing the switching frequency in half. The result should reduce the switching losses by half at the expense of an audible whine and higher ripple current (I think?). It'll be easy to implement as well - just change the micro frequency to 8mhz using the internal oscillator.

The effect on temperatures, however, should be less than half - that is, the temps should be slightly more than half of what they were before due to the other sources of heat (diodes, Rds_on) that aren't changing.

Anyway, this would give us an idea about what to expect from reducing the gate resistance to speed up switch-on/off times, if we decide to pursue that.

Some observations:

1 - The ~8khz whine is not very loud, but it is very high pitch and I found it quite annoying. I don't think I could take it if I had to leave it like that.

2 - I increased Kp in the PI loop to account for the slower processor, but I forgot about the ramp rate. It took what seemed like forever to ramp up in current.

3 - I froze the micro once. Stepped on the pedal too hard - not sure why it locked up, but it did. It was very reliable at 16Mhz, so not sure why it would change - maybe something to do with the overcurrent reset or the response of the PI loop at the slower processing speed? I plan to change it back to 16 Mhz, so I'm not going to worry.

4 - As expected, the 'feel' of the controller didn't change (aside from the slow ramp).

5 - Temperatures. Conveniently, the ambient temp was about the same as in the video a few pages back - 42C. The only difference was that the sun was going down tonight while the video was in the sun, but since nothing is exposed, I think only the ambient temperature matters. I went on the highway pulling the same amps until the temps stabilized. Mosfet and diode were around 61, capacitor was at 65 (had just clicked up to 65 when I got to my exit - might've gone higher?). The heatsink probe was reading 52. If you happened to watch the part of the previous video where the camera is right in from of the probe display, you might remember the mosfet reading 67, diode 63, the capacitor a little lower than that (at that point), and the heatsink probe at 56C.

*Remember, these are just probes that are touching the case of the mosfets/diodes to get a ballpark temp reading.

So, Before at 15khz:
Mosfet - 67
Diode - 63
Cap - 60ish
Heatsink - 56

Now:
Mosfet - 61
Diode - 61
Cap - 65
Heatsink - 51

6 - The switching components ran cooler, but the caps did not. Previously, I had never seen the caps rise higher than the mosfets/diodes. Now, I suspect with the lower frequency and higher ripple current, the caps are generating more heat and are rising in temp.

7 - Previously, the mosfet ran hotter than the diode, but at half frequency, they were roughly the same temperature. Physically, they are fairly well thermally coupled due to the copper heat spreader, so I'd think a close temp is to be expected. The difference in temps before is likely due to the extra switching heat that is now cut in half. When the mosfets were generating a lot of heat before (more than the diode), they ran hotter.

8 - It's always interesting to compare the mathematical models to real measurements. Using the models for a mosfet and diode presented quite a few pages ago, the heat generation at 15 khz, half duty cycle, and 200 motor amps is 449W. Cutting the frequency in half reduces this to 273W, or a 39% decrease. If we assume that the thermal resistance stays the same, we can then say the component temperature-above-ambient should decrease by 39% as well. This hypothetically would give:

Mosfet - 57
Heatsink - 51
diode - should stay the same? It's producing the same heat as before, so...

However, this is not what was measured - the predictions are too low. The actual temperature changes are closer to a 26% decrease in temp, significantly less than the 40% prediction. Of course, there are so many assumptions that go into the model (which itself is just an approximation), so maybe these results are actually pretty good.

So, here are some other model heat gen results to chew on:

15 Ohm Rgate - 37% less heat generation
10 Ohm Rgate - 50% less heat generation
5 Ohm Rgate - 64% less heat generation

[MPaulHolmes]

Man, when you said you wanted to be a beta tester, you weren't joking! I wonder what caused the latching. I'm going to make the next one with a LEM 500. I don't know if that has anything to do with anything, but there must be a reason they call a LEM 300 a LEM 300 (300 amps hehe, as opposed to 500 amps).

The EVTech people told me that too fast of a change in voltage or too large a voltage into an A/D channel can cause latchup.

Joe, one experiment you could do, (although I don't recommend it) is to turn up the hardware overcurrent shutdown point some (also change the software to allow for higher current) then slam on the gas. I predict at 16 MHz that you would get latchup with the LEM 300. It's actually a very noisy signal. I looked at it on the oscilloscope. It seems to me to be the most obvious cause of the latchup.

Anyway! Temperature is what we're talking about! Sounds like good savings for the mosfets. Cutting the resistance from 20 Ohms to 10 Ohms could only be done safely if we used 2 mosfet drivers. Voltage spikes would increase. Any idea what they are like right now? 144v isn't too close to 200v, but it isn't really far away either.

One thing to consider: The capacitors are rated for 3000 hours at 105 degC. Right now they are only getting into the 60's so that doesn't sound that bad. Even if they did get to 100 degC, if you drove for 1 hour per day at 100 degC, you could drive for around 10 years.