Saturday, May 19, 2012

More Charging Experiments

Not much to report for a few weeks... Thankfully.

The Winston battery pack continues to do nothing other than sit there and do it's job without fuss, chemical smells, or sudden death.

April's final generation figures were interesting in that they were the same as March's figures.  That's interesting because March was one of the sunniest on record and April was one of the rainiest on record.

May is turning out to be a mixed bag and a bit disappointing.  We had a long run of gloomy days and the main lithium bank hit the bottom a few times.  On one run of bad weather I also depleted both of the backup Ritar lead acid batteries as well, using an old 1kW inverter to run a pair of the lab power supplies to charge the lithium bank during the night.

The lithium battery protection works well, sounding the police car siren at low battery and then shutting down the inverter when the weakest cell gets to 2.999V.

Then during the day after using the Ritar battery, I turn the lab power supplies the other way round and use the solar to recharge the fragile lead acid batteries first.  It doesn't matter if the lithium bank sits at the bottom for a few days without being charged much but the lead acid ones need charging as soon as possible.

I might set up a more permanent hybrid battery system to make use of the lead acid batteries as a "battery of last resort".  Used that way they might last for many years, if only discharged once in a few weeks, rather than every day.

I've also been playing with the lithium bank charge settings.  Cell no. 8 has taken to reaching full charge a bit before the others.  This is a feature of the bank being bottom balanced and the longer absorption charge times I've been playing with (now up to 50 minutes).  At 28.0V absorption level, the cell was getting up to 3.58V before charge end, while the others were getting up to 3.51V.  But cell no.8 rockets up to this high in a few minutes at the end of the 50 minutes, causing the other cells to actually fall a bit.  So I've been winding the absorption Voltage down, a bit at a time, to see at what point the cells will remain close together.

At 27.7V, or 3.462V per cell, this seems to be the case.  Today the pack sat at absorption for the full 50 minutes and all the cells remained fairly close together in Voltage.