Electrical nerds help me. Need solar panel advice.

[pylon]

Ok, I bought 3 of these solar panels:





I want to charge a deep cycle 101 amp hour, group 27, 12V deep cycle RV battery with it.

With a 120 watt array (3 X 40 watt panels), how fast would it charge the battery in direct sunlight?

Do I hook up the panels in series or parallel? I know one is better than the other.

Will the built in 7 amp controller be adequate? Or is there a device I can attach that will allow me to monitor the battery and simplify it by just displaying a capacity bar like your cellphone does.

Help, me confuse by electricity thing.

[ken0042]

I have the exact same panel. Bought last winter, and then in an ironic twist I never ended up dry camping this year.

As for the math, in ideal conditions each panel will give you 2.3 amps of power, so 3 panels will give 6.9 amps. Assuming you are charging from 50% drained (as you shouldn't bring a deep cycle battery lower than that), it would take 7.24 hours to return 50 amps to the battery.

Now ideal and realistic are two different things. Right now you would be lucky to get 1.5 amps per panel for more than 2 hours. The sun is just too low. But I did testing in March last year, and was able to get 1.75 amps around noon.

Personally, I would buy a better charge controller if I was going to hook up 3 panels. Or even look at a single panel with chanrge controller; if you just bought these. I have seen Canadian sellers on eBay offering 120 watt panels with controllers for under $300.

[ken0042]

Oh, and you want to hook these up parallel. The output is around 20 volts, and the charge controller drops that down to 13.5 volts for charging. If you were to hook these up in series (if you even could), you would have 60 volts coming into a charge controller. Or after the charge controller, you'd have 40 volts. However I think you'd let the smoke out of the controllers and/or panels before that happened.

Series is good for taking two 6 volt golf cart batteries and getting 12 volts out of them for your RV. If you had two 12 volt Deep Cycle batteries, they would go in parallel.

[ken0042]

(I'll just keep talking)
100 watt system for $228 shipped

150 watt system for $318 shipped

Same seller on both. The 150 watt system has a better charge controller. It still isn't MPPT (which is the better type), but still good enough.

Why-MPPT-PV-Solar-Charge-Controllers-Are-Important

[pylon]

Ken, would this put out the same power?

Because this looks slick:

http://www.ebay.ca/itm/120W-folding-...item2a30b4740f

[ken0042]

Yes, but keep in mind a Chinese product shipped from California with FedEx ground will cost you easliy $100 in duty. You also still need a controller; the 7 amp ones you have are rated just over what this puts out; by 1/3 of an amp. I wouldn't want to risk it.

[pylon]

I am not adverse to buying a proper controller. I want to keep the whole project under $500. And I want it to provide enough power to charge phones and a laptop during the day, run the furnace at night and run a radio and lights at night for a few hours, and still regain a full charge during the day.

Also I want it to keep the battery charged while in storage. Will this overcharge the battery in storage?

This would be the one I would buy you suggested:

http://www.ebay.ca/itm/150W-Solar-Pa...-/271312678416

I can always return the stuff to Crappy Tire if I have to.

[ken0042]

That controller says it provides overcharge protection. However I will admit I know less about how overcharge protection works.

Speaking of lights, have you converted to LEDs? (Assuming you saw the thread earlier this year about LEDs.)

[photon]

Heh, let the magic smoke out..

[To Be Quite Honest]

Originally Posted by ken0042

That controller says it provides overcharge protection. However I will admit I know less about how overcharge protection works.

Speaking of lights, have you converted to LEDs? (Assuming you saw the thread earlier this year about LEDs.)

I remember Mythbusters saying mosquitoes can't see LED light. That's good! Boooo to malaria!

What about a wind charger as well?