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 hill to home 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 steps down it's output to a lower level at about 164 volts. I have the BMS set to shut off the charger when the first cell gets up to 3.45 volts, and this often happens before the charger reaches that 164 volt step down point. If the charger is running at full output (phase 1) the balancer isn't able to shunt off enough from the highest cell to keep voltages under the 3.45v high end limit, so it just shuts off the charger. This is when I individually add a little bit to the lowest cells.

If I convert another Force to make my climb to home I would seriously consider using 50 or 52 of the 100Ah cells.  Mine settle to about 3.30 to 3.35 volts soon after the charging stops so the pack voltage would still be within the controller's 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.