Solar on a cloudy winter day?

[mtnbbud]

I recently got a deal on a suitcase style 120 watt system with a 20 amp controller. I wanted to test it so I hooked it up and attached it to my old trolling motor battery. The controller indicates it's charging at 12 volts and 0.8 amps.

Is 0.8 amps going to do anything? When attaching this to my rv batteries, is there a minimum amps I should be looking for before charging?

I have two Trojan T105s at 225 amp hours. I thought this panel could help keep my batteries topped off when dry camping.

Thanks Jeff

[mtnbbud]

Thanks for all the replies. I'm beginning to think the panel won't be worth setting out unless it's a sunny day.

I typically dry camp for 3 or 4 days at a time and haven't had any issues since I've switched over to the 6 volt golf cart batteries. I haven't been using my furnace since it really seems to drain the batteries.

I didn't think my old trolling battery was fully charged, but I'll try running a load off of it to see if the charging amps increases. I keep hoping to have the sun break through the clouds to see the panel function in full sun.

[time2roll]

120 watts will do something when the sun shines. For off grid use I recommend 200 to 400+ watts.
For cloudy winter camping you may need more. The ability to tilt panels will help. And you probably need more battery and/or a backup generator system.

[Gdetrailer]

Not a real good test using your trolling battery, some of the charging depends on the discharge state that the battery may be in at the time of hookup.. Hook it up to a fully charged battery and you will get virtually no charging..

Discharge the battery some and try again perhaps?

Add a load to the battery with the panel connected and you should see a bit higher reading from the panel.

.8A for one hr is .8Ahr..

225Ahr of battery with .8Ahr charge, nope, not gonna happen with cloudy overcast weather.

120W isn't going to net you much more than a trickle charge on good sunny days in a large battery. A max of 7A and that is when the panel gets full sun around noon time and you have the panel pointed squarely at the sun..

You have just run into the "Nemesis" of solar charging.. Not much charging happens on a "cloudy" day.

It will help to cover some of your battery usage on bright sunny days, but it isn't going to "top" it off if you use more energy than what the panel can supply for that days conditions.

[CA_Traveler]

Clouds reduce the available amps. 0.8 amps could indicated the battery is charged or shot. With sun, panel pointed at the sun and discharged battery you should get more amps.

Hook a digital voltmeter to the Trojans. The voltage should be about 14.4V for bulk charging and taper to 13.4 for float with no house loads.

For refernce a fully charged battery at rest will read 12.7V and 12.1V is 50% discharged. Look up the exact specs for your batteries.

Yes the panel will help but is limited and won't keep the batteries charged unless you have very minimum usage.