Charging 12v Batteries With 36v Solar Panel ADVICE

[dokken5]

I have three 12v batteries on my R/V. They are wired parallel because I have to stay at 12v for the R/V system. If these batteries are discharged, can I use a 36v solar panel, wired directly to them, without a charge controller, to charge them?

[Mike90250]

Yes you can. But, NO you don't want to. Nothing would be regulating the voltage to the batteries, and when "full" they will start overcharging and bubbling all the water away.

If you are asking if you can disconnect them from the RV, wire them in SERIES and then to the panel - maybe. a 36V battery bank needs 45 or 46V to force power back into it (that's why a car alternator is set to about 14V to charge the 12V battery) With solar, and shorter charge periods, a slightly higher voltage is used to push more power in a shorter time,
As long as you monitor the battery voltage and stop charging when the batteries get to 42v, you will be safer than just letting it go unattended.

[dokken5]

Nah, they wont have a chance at overcharging. I just want to prolong the charge that they have while I am there.

[NEOH]

dokken5 ,
Yes you can.
You might need to disconnect the PV Panel at night.
You should disconnect the PV Panel when the SG indicates 100% SOC or when the battery voltage has been at 14.8 Volts for several hours.
The PV Panel will not be operating anywhere near its Max Peak Power rating - more likely at only 33% of Rated Power at Solar Noon, and worse otherwise!

BTW:
Friends, don't let friends, connect PV Panels directly to batteries without using an MPPT Controller ...