I have a project that requires 24V. I have 4 12V batteries (2 in series/2 in parallel). I'd like to have a solar panel to charge them. The batteries are 55Ah sealed lead acid batteries. The batteries will not be in constant use, so they should have plenty of time during the day to recharge. Does anyone have suggestion on what to look for in a charger that could be used here?

 

MPPT

 

How much current does the project require?
If the current required is low I would be tempted to use a single 12V battery driving a 12V to 24V DC-DC boost converter.
I am reluctant to charge two batteries in series. I usually charge each battery separately on a 12V charger.

 

Lead acid batteries are charged in series and parallel combinations everywhere. Many solar installations have 4 in Series to give 48V. Emergency lighting has up to 240 cells (forty 12V batteries) in series to give 480V. Fork lift trucks have 24 individual cells connected in series. No-one ever removes all the interconnects and charges each cell individually!

When connecting the two pairs in parallel, take the positive supply cable to the positive terminal of the LEFT pair then link across to the positive terminal of the right pair; the take the negative supply cable to the negative terminal of the RIGHT pair then link across to the left pair (or vice versa).

 

How much current does the project require?
If the current required is low I would be tempted to use a single 12V battery driving a 12V to 24V DC-DC boost converter.
I am reluctant to charge two batteries in series. I usually charge each battery separately on a 12V charger.

The product draws about 25-30 amps when at full load.

 

The product draws about 25-30 amps when at full load.

Thanks. That's a lot of current. Forget my suggestions.

 

There are 12V/24V PWM solar charge controllers on ebay for not much money. MPPT charge controllers can eke out a bit more efficiency, but if you're just keeping some batteries topped up, that's not likely to be worth the extra money. Then you just need two panels in series; wattage depends on how much energy per day you need.

But it is possible to charge a 24V battery from a single solar panel (maximum of 300 watts); there's this MPPT charge controller which claims to be able to boost voltage from a single panel to charge batteries ranging from 24V to 85V. I have no personal experience with it, but I want one.
https://www.fnxsolar.ca/tourix-gen-3