Thursday, October 07, 2010

Lithium Update


With about 3,500 miles on the Lithium batteries, that's about 80 charge cycles, everything is working well. We make the climb up the long hill with ease now, even with groceries and a passenger. Driving the car is more enjoyable now so I find that I drive her more often. I think I'll even put in a nice CD player.

I occasionally need to top-off a few of the Lithium cells individually because my charger doesn't step down it's output until it reaches about 164 volts. The BMS shuts off the charger when any cell reaches 3.55 volts, which often happens before the charger reaches that step down point. With such high output the balancer can't shunt off enough to keep voltages under the limit, so it shuts off the charger. I had the charger re-programed (again) to step down from the high output at around 164 volts. This was as low as they could go with the Zivan NG3, but it's still too high.

When the BMS gets up to where it is balancing (shunting?) about 35 to 40 cells and it's over about 80 degrees outside the BMS unit gets too warm and shuts everything off. This is with the trunk open, parked in the shade, with good airflow. I can still charge the pack by turning off the balancing function. This over-temp shut off didn't happen when it was 60 or 70 degrees outside.

If I converted another Force to make my steep climb home I would seriously consider using 50 or 52 of the 100Ah cells.  Mine settle to about 3.40 to 3.45 volts soon after the charging stops so the pack voltage would still be within the controller limits. I'd also consider using a more robust balancer so that a single cell running up in voltage doesn't shut off the charger before it reaches the step-down voltage.