Paul & Sabrina's cheap DIY 144v motor controller

[MPaulHolmes]

I drilled and tapped two holes in the copper heat spreader, and drilled 2 holes in the aluminum heat sink, then sanded down both surfaces with 600 grit sand paper, so they are both super smooth. Then I bolted the heatsink to the heat spreader and they lay perfectly together, with no hint of daylight between them. I think it will work really well.

[motor_control]

You need use hit transfer paste IMHO.

[MazdaMatt]

NiHaoMike, I was not implying that a flyback transformer should be used to power the vehicle. I asked the electrical engineer about replacing the diodes with mosfets and she told me to look up how that is done in a flyback transformer circuit for an example of how it should be done with a motor.

Paul, there may be mosfet drivers that have built-in flyback control. I will research further. This would be sweet.

[MPaulHolmes]

Motor_control: Don't worry, I have some thermal grease in the garage. I was just testing it to see if there were any gaps when bolted together. Do you know if the inductor that you suggested on the AVcc pin will cause an inductive kick when power is cut to the ATMega8? Do I need a freewheel diode there, or is it OK?

Thanks Matt!

[motor_control]

Originally Posted by MPaulHolmes

Do I need a freewheel diode there

No. See "Figure 96. ADC Power Connections" in mega8 datasheet.

[NiHaoMike]

Originally Posted by MazdaMatt

NiHaoMike, I was not implying that a flyback transformer should be used to power the vehicle. I asked the electrical engineer about replacing the diodes with mosfets and she told me to look up how that is done in a flyback transformer circuit for an example of how it should be done with a motor.

Paul, there may be mosfet drivers that have built-in flyback control. I will research further. This would be sweet.

A DC motor controller is actually much more like a buck converter than a flyback converter. The commutation diodes provide a path for the induced current to flow. The controller will work as a boost converter during regen, however, so it would be necessary to also use commutation diodes on the high side.

The circuits used to provide a path for leakage inductance in flyback converters are not practical for use in motor controllers. A PC power supply I have that is based on a flyback topology has a capacitor from the drain of the power MOSFET going to a pair of fast recovery rectifiers, with an inductor in the low side to limit peak current when the MOSFET turns on. To use the same design in a motor controller would require a large, expensive capacitor with a high peak current rating.

Synchronous rectification actually is generally not worth it at high voltages. But since a DC motor controller already has the correct topology for it, it wouldn't cost much to include it.

[MPaulHolmes]

Now this is an oversimplification, but it's not too bad of an estimate:

The pack voltage is irrelevant.
Let's say you are running at 50% PWM duty, 500 amps. The diodes conduct half of the time. So, the power loss from them is...

1v*500amp*0.5 = 250 watts waste heat.

Now let's use mosfets instead of diodes. Say 10 in parallel. My 200v mosfets have a typical resistance of 0.0085 Ohms each. So, at 500 amps, 50% duty, the loss is...

0.0085*500*500*0.5*0.1 = 106 watts. Not too shabby! The mosfets I'm using are $5.50 each, and the diodes are $4 each (unless you get them from this one place that is out of them for the next couple months. Theirs are $2.50 each I think).

144 watts of heat is quite a bit. Has anyone ever grabbed a 100 watt light bulb? Those things are hot!

[Christ]

Paul - Relating to "Coppers" and their composition - you only have to add Lard to that, and you get... well, you know.

Regarding heat -
1. Arctic Silver. It's a little more expensive, but it works the best of just about all the pastes in the home-modder range.

2. Did you get the links on Lapping? With lapping alone, Lou (the guy on Metku) was able to get his CPU 10* cooler... might be something to look into.

3. What's keeping anyone from mounting the controller inside the car, or venting the heat from the controller (the 106 watts of heat-waste) into the cabin for partial heating during winter/cooler weather driving?

4. Liquid cooling, using the same heating solution that has been suggested for liquid heating in the vehicle to begin with?

[MPaulHolmes]

I got the diodes soldered to the PCB. The mosfets are a little tougher, because they need a couple resistors soldered too. So, there will be some drilling required.


Front view


Back view!

Good enough for government work.

The careful observer will notice that version 0.1 will be 144v 500amp (50 amps per diode).

[MPaulHolmes]

Originally Posted by Christ

Paul - I want to marry Oprah! -

What!? I hear she's not with Stedman anymore... Hahaha! I like messing with quotes.

Originally Posted by Christ

2. Did you get the links on Lapping? With lapping alone, Lou (the guy on Metku) was able to get his CPU 10* cooler... might be something to look into.

I read the guy's process, but I don't know if I saw lapping. I still don't know what that is. boohoo! Makes me mad!

Originally Posted by Christ

3. What's keeping anyone from mounting the controller inside the car, or venting the heat from the controller (the 106 watts of heat-waste) into the cabin for partial heating during winter/cooler weather driving?

Excellent idea! I like it! You have to keep the cable from M- on the controller to the motor as short as possible, but maybe it could be placed somewhere up front, up in the vents or something. I love the idea of the fans blowing on it. You could even have the inside exposed a little to the outside air, so the fan would really keep it cool.

Did you see the advertisements for the new Fast and the Furious?