Solar panel ??

[moparguy]

We're on the verge of leaving for a little over 2 weeks of elk camp and I've got a question on the use of two solar panels I've come up with. My plan is prolong the life of the 12v batteries we use to power our tent lights.



One panel is blue glass (126 sq. inches), the other is dark brown (66 sq. inches). The blue one puts out 9. 75v in full sun, the brown one 10. 9v in full sun. Was not able to check amp output since we had the multimeter set on 250ma and blew the fuse.

The blue panel does mention 1. 2 amps on the specs tag, but to a photovoltaic dummy, that sounds wrong.



My question is how to best take advantage (cheaply) of these two panels. Since the batteries are 12v and neither panel makes 12v, how much benefit should we expect to see. One opinion is that any positive flow is better that a discharge. Makes sense to me.



Since we leave in 4 days, I don't have time to order anything to maximize this application, just looking for simple home-brew solutions to get the most power into our battery.



Thanks, Ronnie

 

[nickleinonen]

in general, the higher the voltage something has, the less amperage it produces/draws, the lower the voltage, the higher the amperage it produces/draws... the bigger surface area makes me think that the blue one will produce its 1. 2a on a good warm sunny day



ie... a 100W light bulb running on 120v requires less than 1 amp of power [0. 834 A] while a 100W light bulb running on 12v requires 10x the amperage to produce the same output





it's been a while since i was in electronics class so i might be wrong...



P = E x I

E = I x R



P= watts

E= voltage

I= amperage

R= restance



i can't find my school notes right now and i am going by memory. if i am wrong please someone point it out... . thanks

 

[illflem]

The voltage is of no concern.

Your biggest worry is going to be overcharging the batteries if you don't have a regulator and it's sunny out.

 

[klenger]

Hooking up either panel by itself will do nothing to charge the battery. Hooking them is series will add the voltages together. I think that you could do this with little chance of hurting the battery because the panel output is such low current, the voltage will not climb high enough during a single day to overcharge the battery. The voltages that you specified are most likely open circuit voltages. The load of charging the battery will drop the panel output voltage to a couple tenths higher than the battery voltage.



Trust me, ... I dare you.

 

[Rotty]

Make sure you put a diode in series of the correct polarity and when it is hooked up to the battery. This way with no sun it will not discharge the battery.

Deffinently series connect them.

 

[KBennett]

Wire them in series

I agree with klenger. Wire them in series. A diode is a good idea as well. Connect the - of panel 1 to the - of the battery and connect the + of of panel 1 to - of Panel 2. Connect the + of panel to the Anode side of the diode and connect the Cathode(striped side on a black plastic diode) to the + side of the battery. Radio Shack should have the diode, 1N5401 or better. Get something rated for 100V and 3 amps minimum. You will lose about a volt across the diode as well but it will prevent the panels from sucking power from the battery at night.



I can put together a simple drawing if you need it.

 

[moparguy]

KBennett, first of all welcome to the TDR.

And then thanks all, for the suggestions. I will connect the panels in series.



Klenger, you had me totally convinced that your advise was definitely the way to go, but that "trust me, I dare you" bit kinda had me wondering for a moment .



Ronnie