Wednesday, December 31, 2008

Battery Degradation

Ugh. I think my battery pack is slowly dying after 8600 miles and 1.5 years.

My Zivan charger alarm has gone off for the past week and I finally looked into it. Apparently the alarm is indicating a timeout that the charge cycle is taking too long for the capacity of batteries that I have. If I charge overnight, I wake up in 40 degree weather and the pack is very warm, around 80 degrees with vigorous "boiling."

After doing some analysis yesterday, it looks like the batteries are not getting past the initial "bulk" charging phase. The charge curve in my Zivan dumps maximum current onto the batteries until the voltage reaches 171.6 volts and then holds it there until the current dies down before putting a final equalizing charge on it. I found that the whole pack during bulk charge never gets above 170 volts, even after several hours of charging. It seems like the plates are sulfated enough to reduce their capacity and reduce the "gassing" voltage significantly.

After contacting Zivan tech support, they said that lead-acid batteries typically get 400 deep cycles or 800 half-cycles at best. If my average trip is 20 miles between charges and I have 8600 miles on the car, that means about 430 half-cycles. This seems a bit low to me, but since this is my first EV, perhaps I treated the batteries poorly the first time around.

With the significant gassing happening, the front luggage compartment also has some acid rust under the front box (similiar to the "hell hole" in the original 914 engine compartment). I'm a bit disappointed, but it's been a good run.

On a side note, I also blew a fuse yesterday after cleaning out the rear trunk because I pushed two of the fast-on connectors together under one of the tail light assemblies. If your fast-on connectors under the tail lights don't have heat-shrink tubing around them to prevent shorts, I hightly recommend that you add it. It only takes 15 minutes and will save a lot of headaches.

Happy New Year