Charging telemetry data--take 1

["Christopher Zach" <czach@computer.org>]

Ok, I came home, and plugged the PC into the Dolphin. Then I powered up.

The Dolphin has a counter that controls the fuel gauge. Currently it reads
100%. The battery pack voltage at rest was 320 volts (25 12 volt batteries
per string, 2 strings.)

Works out to an average of 12.8 volts per cell. Hm.

I then plugged in the charger. When at 100%, the controller brought the pack
voltage to 400 volts at about .5 amps. This appears to be the "trickle
charge" mode designed to equalize the batteries (high voltage, low current)

I then fired up the car and drove up and down the steep driveway hill.
Voltage at full power was in the high 290's (I have to check) with a power
output of about 35kw (120-130 amp draw). From a 52amp/hr pack how is that
for sag?

At the end of a few ups and downs, the pack was down to 97.5% by the
counter, and still at about 320 volts at rest (ok, 319).

I then plugged in the charger. After a few minutes to let it get up to steam
(normal) it was reading a pack voltage of 331 volts with a charge current of
3.3 amps for a 1.1kw charge. Line voltage was 111 volts (down from 121 idle)
at 12.8 amps (the max the controller will take, I can adjust this)

The batteries are now 97.8% full. Here is what I am wondering:

What if the problem is this: The system has this neat counter that watches
current go in and out of the batteries. When the *counter* reaches 100%, it
declares the batteries "full" and does 8 hours of trickle charging at 400
volts/.5 amps. Then it shuts down. This will keep the controller from
overcharging the batteries.

But over time, the counter becomes out of whack with the "truth" of the
batteries. The counter thinks "full", but the batteries will still want a
bit more charge. But they don't get it. Time passes, and the max charge of
the batteries becomes less and less.... This sort of bears up in my test;
after 30 miles the gauge read half full but the batteries were tired.

Now, being the guy I am, I apparently can reset this number to anything I
want. The question is should I reset it to something like 90% when it thinks
it's full to give it another 10% of "overcharge"? Will I run the risk of
damaging the batteries? At what voltage should this pack read "full"?

To be honest, the pack might be only 60% full. And the fact that it's
happily sucking max power right now (3.3amps) makes me wonder about that.
I'll watch it and see if it goes to trickle simply because the counter hits
100%.

Thoughts and comments from the battery crowd? The biggest thing I may have
going for me right now is that this pack only has 1,800 miles on it; it
might be saved...

Chris