It occurs to me that adding all the diodes will probably cause an issue with the solar charger. When it's first connected, it looks at the battery voltage to decide whether to use 12 volt or 24 volt mode. At night it takes its standby power from the batteries - which it won't be able to do any more. Also, it won't be able to monitor the battery voltage.
Hmm. That's a pain.
So, as a hacky solution, what would be the effect of just not using diodes on the first battery, like this:
Note that the first battery (A) no longer supplies the load directly either, or it would end up doing all the work.
Tell me if I've got any of this wrong (I'm assuming a 0.5 v drop across the diodes):
- When under charge, all batteries will get charged up, but batteries B~n will always be 0.5 volts less than battery A (so they'll never quite charge fully, hey ho, but at least the charger will cut off too soon rather than too late)
- When no longer charging, there may be a little bit of leakage from battery A out to the rest of the batteries as they self-discharge, but battery A will never drop to less than half a volt above the voltage of the rest of the bank
- When discharging - and this is where I'm a bit hazy - batteries B~n will provide almost all the current, but some will come from battery A through both sets of diodes
- When no longer discharging, battery A will discharge into the other batteries only up to the point where it's voltage is half a volt over them.
Side effects:
- The charger will go into 'float' mode half a volt too early for most of the bank - which I may be able to get around by telling the charger it's connected to a Gel battery instead of SLAs (Gels, apparently have a float voltage 0.5v higher than wet SLAs)
- The load will see half a volt less than it's used to
It seems to me that this could work. Does it seem like a bad idea? Am I right in thinking Battery A could actually be a tiny battery - it's acting more like a sorta voltage follower than as a store of power?