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Old 04-09-2009, 06:40 PM   #827 (permalink)
MPaulHolmes
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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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Quote:
Originally Posted by bennelson View Post
My ammeter shunt is in series in the string of batteries, so I am measuring battery amps. I always felt that's the number to watch, because the batteries care a lot more about how many amps you pull than the motor does!

Anyone have a spare analog 500 amp ammeter kicking around? Mine only goes to 300!
You can get like +/- 5% accurate using the copper cable from the controller M- to the Motor as the shunt. Then, just use a cheapo $2.99 volt meter from Harbor Freight set on the 200mV setting, and convert the measured voltage across that cable into current by doing I = V/R, where R is the resistance of your cable. It will be a tiny resistance. How long is that cable? What gauge cable?

The reason the controller senses motor amps is to protect the mosfets and diodes. It's also a really good idea to measure battery amps, to keep them safe too. That should be a feature we add later.
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