Jeffs Zenn #2

Posted: October 11th, 2008 under BSD General, On Road EV.

Jeff has been driving his Zenn for 10 months now. He found that his batteries had about twice the capacity that the in-dash “Fuel Gauge” indicated, and that the BatMan3-EV was much more useful than what Zenn provides.

They had drained their batteries a bit more than they should have a few times. The problem would occur when they had been on a long trip, and they arrived at the bottom of the hill they live on with the batteries pretty tired. They had one case where passengers had to get out, in order for the car to make it up the hill. This probably is the reason that recently Jeff found that the capacity of his pack seemed to be falling. He brought his car over to my place, and over the course of a Sunday, I charged and discharged each battery individually to find the capacity of each battery.

My method was to use a power supply set to 14.76V to charge up each battery, just before I discharged it. I discharged the battery using a BatMan3-EL in drain mode, with a contactor connecting and disconnecting the 0.25 Ohm 1000W resistor, ending the test when the voltage comes down to 10.5V. This starts out at a bit over 40A, and as the battery gets tired, it comes down to around 33A. The BatMan3-EL records how long the load was connected, and how many Amp/Hours the battery produced in the process.

Here are the results, with battery, starting voltage, drain time, Amp/Hours:

1. 13.302V, 99:17, 58.46A/H
2. 13.298V, 91:15, 52.44A/H
3. 13.333V, 109:21, 63.09A/H
4. 13.328V, 101:19, 58.52A/H
5. 13.303V, 96:49, 56.49A/H
6. 13.260V, 95:20, 55.10A/H

Now we didn’t have the opportunity to do this test when the batteries were new, but we can see that battery 2 now has only 83% of the capacity of battery 3. After this test we adjusted the BatMan3-EV capacity in Jeffs Zenn to 45A/H to make sure they didn’t damage the batteries any more that they already had.

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