Tuesday, February 19, 2013

Bottom Balancing night

Last night, I continued draining the brand new CALB Battery pack, by setting a lower limit of 22.5V on the programmable dual relay voltmeter and watch carefully that the cells were going down at the same pace; 

Once the pack voltage reached this 22.5V, all cells were around 2.81V and the relay opened, opening the Tyco Kilovac contactor, stopping the cell's bleeding: Cells voltage immediatly bounced back to 2.90, 2.95 and a little later they were all around 3V

Then I started to bottom balance each cell, using my low cost bottom balancer

I had to cut the voltage reading wires and use other smaller clamps to get the voltage from the cell terminals directly - and not from the draining clamps, giving an inaccurate lower voltage -; I then changed the lower limit from 2.45V to 2.73V and upper limit to 2.76V

With this modification, the cell is really drained until its voltage reaches 2.73V, then it bounces back up slowly to 2.76V, at this point the relay kicks in and the resistor bleeds the cell again down to 2.73V, etc
I end up at 2.75V for each cell very effectively now

New crocodile clamps for direct terminal voltage reading, much better ...

This morning I have 5 cells done out of 8 ... but resting all day the cells will be back to maybe 2.80 something tonight, and I will go through the bottom balancing process again

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