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Old 12-31-2008, 10:32 PM   #60 (permalink)
MPaulHolmes's Avatar
Join Date: Feb 2008
Location: Maricopa, AZ (sort of. Actually outside of town)
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Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000
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Controller mostly done

The controller is mostly assembled. I decided to put 5 mosfets and 5 diodes in it, so it should now be a 84v (well, anything safely under 100v) 100amp controller if it wasn't for the crappy bus bars (ghetto 13 gauge wires). The weak link is definitely not the mosfets I think.

I was able to drill the aluminum using the trick an ecomodder told me about dropping alcohol down the holes as you drill. It's almost impossible (for me) otherwise.

The white stuff on the aluminum heat spreader was thermal grease. You are supposed to put as little on it as possible. Too much is worse than none. It fills in the microscopic holes.

I didn't have a good way to attach the stupid current sensor, and I cooked it (soldered too long!), so that's like $5 down the toilet. Fortunately, I won't need current limiting in this version, because there are plenty of mosfets and diodes to handle the current that the bike motor uses. I'll get a different type (easier to use) of current sensor for the car's version.

A better way to remove heat from the mosfets and diodes is to directly attach them to the aluminum heat spreader (with no mica backing), and then put some sort of layer of mica or something between the heat spreader and the outside heat sink. I didn't have a big piece of mica so I did it this way, which is OK in relatively low power applications like a bike controller.

I need to add a few more things to the micro-controller's program, like high-pedal lockout.

I need to figure out how to do the 2 wire throttle instead of the 3 wire version. I need to add an on/off switch, then try it on the bike, but it's really exposed to the elements, so maybe I should put it in a box first. I don't know.

I'm super tired and my fingers don't want to move to type. I shouldn't have worked in the garage with the door open for like 8 hours. I didn't notice the cold until I was done. Now I think I'll get pneumonia.

Man, soldering those mosfets and diodes onto that 5 oz. copper PCB was truly horrible. It was impossible with a normal soldering iron, so I had to use the soldering gun, which people say is bad to do. Oh no, it's too hot! It's the only way I could melt the solder though. It was so annoying soldering, that I really want to make a mean reference to a famous talk show host, but my wife won't let me.

I think the car's version will actually be easier, because the larger 200v mosfets have wider legs. Those stupid ones I am using were too close together. Oh, that makes me real angry way down deep inside.
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kits and boards

Last edited by MPaulHolmes; 12-31-2008 at 10:50 PM..
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