It's not something I planned, but now I have a spare battery bank for my off grid 24 volt solar system. I bought new batteries, and the old ones are still good. These are 6 volt golf cart batteries. Right now I'm not doing anything with the old batteries, but I don't want them to just sit there. For the time being, could I connect these batteries somehow as part of an A/B switch, where I could manually switch from one battery bank to the other?
I have two battery banks, and I've done something like what you are describing, but for a different reason. I have a total of four 6volt batteries wired in pairs in series to get two 12 volt banks. The charge controller is attached to the minus terminal of battery 1 and the plus terminal of battery 4. The minus terminal of 1 is also connected to the minus terminal of 3, while the plus terminals of 2 and 4 are connected to each other.
The minus to plus connection between batteries 1 and 2, and also 3, and 4 are attached with wingnuts. Periodly whenever I want to equilize one bank or the other, I unscrew one wingnut between 1 and 2, or 3 and 4 (but never both). That way, 100% of the solar power can be directed at one bank at a time untill that bank is 100% charged (as indicated on the charge controller). In this way, one bank or the other won't pull down the efficiency of the other bank.
I spoke to a guy at the Solar Living Institute and he recommended something called a pergo switch often used in marine applications to manually switch between battery banks. I think it would be like $50. Most likely I will do that, but I'll look into the details.
I had considered adding a separate solar array, as you mentioned, but right now it wouldn't make much sense for me.
What kind of charge controller do you have? That sounds like a great feature. I don't know if mine has such a feature. Not that I am complaining.
bob day wrote:my controller has an option that when the main bank is floating, excess charge can be routed into a second separate system, and i think many of the newer controllers have that same possibility
another option might be to separate off an odd panel for the second bank, depending on your setup
it's an mppt controller of some sort-- that switch you mentioned might be useful to switch between banks on the load side when you've run your A bank down, but an automatic switch would be better for the charging side, also, you probably wouldn't be handling high currents on the charging side
In fact, thinking about it, unless you're running real high amperages i doubt you would need a switch that heavy, i believe he may be talking about a switch that will handle starting current for an engine
oh well, just idle thoughts,, if you have a half decent controller, see if there's another set of outputs there, most likely that's for the overflow charge
steven harris does something similar at www.battery1234.com and also www.solar1234.com
he does it in his truck, i have been trying to recreate one of his backup battery systems for my vehicle to act as my main energy source, hook it to solar and the alternator to charge.
great podcast he does with jack spirko. google it-
for backup battery systems you keep in the vehicle there is a switch that only connects the backup into the circuit when the alternator is charging--name of the switch slips my mind, but they are pretty cheap and available on ebay--less than 10 or 20$
also though, trying to recharge a large depleted bank from a standard car/truck alternator may be a bad idea, most alternators are not meant to provide heavy charge currents over long periods of time, so you may need a heavy duty alternator--some warn you that even a single battery needs to be brought up to a certain voltage before attempting to charge it in the vehicle
i believe i've heard that guy talk on JS
Fire me boy! Cool, soothing, shameless self promotion:
100th Issue of Permaculture Magazine - now FREE for a while