View Single Post
Old 10-24-2009, 10:17 PM   #2496 (permalink)
MPaulHolmes
PaulH
 
MPaulHolmes's Avatar
 
Join Date: Feb 2008
Location: Maricopa, AZ (sort of. Actually outside of town)
Posts: 3,831

Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000
Thanks: 1,367
Thanked 1,115 Times in 730 Posts
So, I had finished another beta controller, but with the $8 super fancy schottky diodes that are rated at 120 amps instead of the other ones that are rated at 60 amps. It was going to be shipped out already, but never mind, it's a long story. I made a little circuit that Fran had suggested to measure voltage spikes. It's so dang freaking elegant and fancy and awesome and dang it was awesome and cool. Joe told me about it. Voltage spike magnitude is a function of current. It's independent of pack voltage. So we can come up with a graph of voltage spike magnitude as a function of current for current = 0 through maybe 509 or so. haha. Well, it might not be "voltage spike magnitude". It would be better to call it the "peak voltage that the controller ever sees from M- to B-", since the pack sags the more current you suck out of it! But who gives a dookie?! All that matters is HOW HIGH IS THE VOLTAGE GETTING??!! We just need to stay away from 200v. Well, I guess 200v is even OK a little every now and then, since they are "avalanche rated". I totally know what that means. I'm not lying.

Now to the results!

OK, First I made the awesome little circuit. Then I precharged the caps and watched on the dedicated volt meter what the max voltage was from Drain to Source. The volt meter started off at 78v. Then I drove around and finally managed to get the peak voltage all the way up to 85.0v I think. It was either 84.5 or 85. I have a bad memory. hehe. That was probably a few hundred motor amps, but I am not sure. I was in 2nd gear at low rpm on a small uphill. So, maybe figure for a spike of 7 volts above max pack voltage? Not bad. Joe's controller has M- B- and B+ all out the same side. I wonder if that makes any difference compared to how it is with the controller I was testing as far as spikes go.

If 7 is the spikes above max voltage, then it's officially safe to drive around at 193v. hahahaha. Just kidding.
__________________
kits and boards
  Reply With Quote