The next day (11 Dec) I continued with the discharge test and ran the motor from 5.30am at around 1000 to 1500 watts until after about 4 hours the low voltage alarm sounded. The cell with low voltage is not the same one that gave trouble before.
The low voltage showed up at a draw-down of 130 ah, which is 70 ah short of full capacity. I know that this cell was not brought up to full voltage at the last recharge. Only two cells got to full voltage and in my impatience to test the pack, I didn’t wait until all the cells protectors went red. This result just confirms that the pack is unbalanced due to me leaving the cell protectors on some cells, and not on others, while I was in the boatyard. (There is small current needed by the cell protectors and so they slowly drain the cell when left connected.) So I need to recharge the pack and make sure it is properly balanced by having all cells at full voltage.
For a few days I recharged the pack using sunshine, and then on 15 Dec borrowed a 48v charger from Claude Desjardins and pumped in about 70 ah until one the cells reached full voltage. This 240v charger puts in 15a and this is way too much for the cell protectors to dissipate so I now have to continue the charging using solar. The solar charger runs at between 1 and 2 amps depending on the state of charge of the house batteries (which it feeds off), and even this is a bit high for the cell protectors so it needs watching.
I also have an “automatic” dc-dc charger which I cobbled together using a voltage sensitive switch and a dc-dc converter. This also runs at 1 to 2 amps but is intermittent. Switching on and off according to the house battery voltage. The intermittence is just about right to give a nice trickle charge that the cell protectors can shunt.
This morning there are still only two cells that have reached full voltage and the pack has just about recovered the amphours used by the drawdown test. As the day goes on I hope to see more cells ‘in the red’.
P.S. I updated the history page with some photos.