Electric Vehicle Project
Another new pack, and a good summer
November 2004
It's been a busy year for the Electric Prizm. Back in the winter of 2003, I noticed that the new pack that I installed in April was having problems. Specifically the range was only around 15 miles, and while the performance was great it would fall like a rock once you hit about 12 miles of driving. Not too very good; something went wrong.
So in April of 2004 I dropped the pack yet *again* and checked it out. The batteries basically were dry because when I did a charge with the MagneCharger while watching the voltages, some of the batteries were going *over* 16 volts while others were still at 13 or so. This caused the high batteries to dry out (boil their water) which made them even more likely to shoot high on the next charge. Positive loop; you wind up with a dry pack which while being a lot more "stiff" when charged (I could easily pull 200 amps and maintain 12 volts per battery) would fail when the electrolyte became drained.
Oddly enough when I saw this I figured out a way to put water back into the batteries (I'll have to describe that someday) and wound up getting most of the capacity back. Still, it's a string of 50 batteries so it was time to spend another $2,500 and get yet another pack from Surplusev.com.
The new batteries arrived and in they went. Much better performance; back to over 35 miles of range without problems. This time though I made some changes to the charge profile.
First, the Magnecharger. Before I was charging at full current till the batteries hit 375 volts, then going to 390 volts, then holding 390 volts for an hour. Bad idea; when the pack is at 360 volts say some batteries may be full yet are still getting hit with a full 20 amps of charge current. More than enough to boil the electrolyte.
So I changed it. I limited the MagneCharger to 8 amps max (down from 18) and let it charge the batteries to 350 volts. Once you hit 350, things change: The charger drops the current to 2 amps (1 amp per string) and slowly charges at that rate to 375 volts. This results in the slower batteries keeping up, while at the same time it keeps the full batteries from getting creamed with current. They will still gas, but since the charge current is less than an amp the Hawkers can recombine the gasses and not vent. Very important.
Once it hits 375 volts, the charger holds that value for 60 minutes, then shuts off. Max current here is 1amp (.5 amps per string). Nice and gentle. With this charge system and a CEF of 95% I can bring the pack to within .2 amps of full. Every 4 or 5 charges I let the Dolphin charger charge the pack. While stupid, it charges very slowly (2.5 amps) and takes the batteries to 390 volts for 50 minutes (at .2 amps) for a nice equalize.
So far this seems to be working. No difference in range, other than what one would expect due to the new cold weather this fall. We'll see how the pack looks in the spring, but if I toast another pack I'm going to NiCds.