trickle charging large battery bank with small panel

Re: trickle charging large battery bank with small panel

Usually, around a 1% rate of charge is good for Maintenance charging (put the two 6 volt batteries in series for 12 volts):

17.5 volts charging * 220 AH * 1/0.77 panel+controller deratings * 0.01 = 50 Watt panel
50 Watt panel / 17.5 Vmp = 2.9 amp Imp

I would still suggest a charge controller:

SunGuard 4.5 Amp 12 Volt Solar Charge Controller (cheap)
Morningstar SunKeeper Panel Mount Controller 6 Amp (has LED for status)

If you get the first one, probably should take a volt meter out once a month and check the batteries are still fully charged.

If you get the second one, you can just glance at the bi-color LED for status...

Since you already have the 10 watt panel--Go ahead and use it. Go out once a week to once a month and check the battery bank voltage (at night, you want to batteries >12.6 volts, during the day you want them >13.2 volts or so when charging/floating).

Once a month check the water level (you are probably not going to boil them dry with a 10 watt solar panel and no controller).

If the batteries slowly discharge, you can bring out battery charger on an extension cord once every month or three and give them quick charge (8 hours? depending on charger used).

-Bill

Re: trickle charging large battery bank with small panel

Just using our typical deratings... But I am sure that 40 watts will work fine too.

-Bill