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Old 06-04-2010, 09:31 PM   #133 (permalink)
RobertSmalls
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Join Date: Aug 2008
Location: Buffalo, NY, USA
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Prius C - '12 Toyota Prius C
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I've assembled a simple grid charger for the stock battery pack from Mike Dabrowski's plans. It's just three adjustable 42V-54V power supplies in series with a 350mA constant current power supply. When assembled and adjusted, it's a 170VDC constant current power supply. The datasheets say it should be around 85% efficienct, and my kill-a-watt confirms this.

I'm looking forward to nightly grid charging and more liberal use of electric assist. In addition to keeping the gas engine's RPMs down by relying on the electric for acceleration, I'll also be displacing some of my gasoline use with electricity. My utility promises they're buying me 100% renewable electricity, so it's arguably guilt-free propulsion.



That's a picture of the charger screwed to a board, with the IMA case open. The charger doesn't get terribly hot, so I'm going to permanently install it inside the IMA box, behind the battery fan. There's lots of room.

The grid charger has some drawbacks. Foremost, it's slow. 350mA into a 6500mAh battery at 70% DOD requires 13 hours. Add another 6 hours or so if you also run the DC/DC converter to recharge a discharged 12V battery, as I plan to do some of the time.

Secondly, the charger has no charge termination scheme. That's the reason it's slow. It just keeps charging, even once the battery gets so full that it dissipates all the incoming current as heat. 350mA is slow enough that the amount of heat generated (65W) is easy to dissipate, but I'd prefer not to waste the electricity.

The plans call for just leaving the battery fan running whenever you're charging. Instead, I'm keeping Honda's BCM powered up (along with the high voltage contactor and DC/DC converter). The battery fan will turn on only if it gets too hot. No more cold batteries in the winter. This also keeps the BCM abreast of the true state of charge of the battery, avoiding the recalibration you'd otherwise get.

I'll do an IMA-heavy run to the Home Depot tomorrow and we'll see if I can beat my usual 40-50mpg on that 3 mi round trip.


Now, can anyone recommend a weatherproof three-wire interconnect I can use for where my power cord exits the car?
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