New solar panel questions

[Manfred]

Hi all - my 2005 Northstar 850SC solar panels are no longer working. They are two flat panels adhered to the roof; not sure the type but maybe 50W or 100W. I purchased one 100W panel and will be installing over one of the existing panels. Do you think I can use the existing wire and controller? I believe the wire is 14 gauge. I was going to leave the connection from the controller to the two batteries, one hot and one ground from the controller that are split off to provide power to both batteries. Any problem charging both batteries with the one 100W panel? Thanks

[Manfred]

JFNM wrote:
I agree, it sounds like you have a battery bank made of two batteries connected in parallel. Assuming that is correct...

Going back to your original question, the 100W panel will charge the battery bank. However; keep in mind that 100W is slightly less than 7.5 amps at 13.5 volts (minimum charging voltage) and that assumes the panel is working at 100% (they rarely do that). So, it is not a lot of charging but certainly better than nothing.

Thanks for the insights. You're right, one 100W is better than nothing. :)The new panel arrived today so I'll get it hooked up and see how everything works. We're heading out on a 6 day dry camping trip in a couple of weeks. If all goes well I may add another 100W to replace the 2nd panel.

[JFNM]

I agree, it sounds like you have a battery bank made of two batteries connected in parallel. Assuming that is correct...

Going back to your original question, the 100W panel will charge the battery bank. However; keep in mind that 100W is slightly less than 7.5 amps at 13.5 volts (minimum charging voltage) and that assumes the panel is working at 100% (they rarely do that). So, it is not a lot of charging but certainly better than nothing.

[Manfred]

I do not believe any controller can properly charge two independent batteries from one pos/neg cable. The controller needs to sense battery voltage to know "how" to charge the battery - if there are two batteries connected (not a bank), the controller will not be getting accurate information. Are you sure you do not have two 12V batteries wired together in parallel to create one 12V battery bank? (a charge controller CAN charge a bank of batteries).

The existing set-up is as follows:
A hot and ground come from each panel.
The two hots are twisted together with a pigtail hot going to the controller. There is a 20 amp fuse before the controller.
Two grounds go to the controller.
One hot and one ground come from the controller; Another 20 amp fuse.
The one hot and one ground are split with a hot and ground going to one battery and a hot and ground going to the other battery.
Each battery has a hot and ground coming from, I'm assuming, the inverter; I can't get a good view of the connections without taking out the inverter.
I have appx 6 feet of 14 AWG from the panels to the battery.

The set-up looks like it was done by the manufacturer. I'm guessing parallel battery connections?

My plan is to disconnect the one hot and ground from the second, non-functional panel; I will disconnect before the controller. Anyway, the new panel is coming in a couple of days, fingers crossed.:) Thanks for the advice/considerations

[DWeikert]

Probably still be a good idea to check at the panel. I know I would be upset if I replaced the panels only to find the problem was a wire corroded through. Odds are the original panels use a terminal block for the wiring and not the modular MC4 connector. If the terminal block isn't properly protected from the elements, you could get corrosion.

[JFNM]

You will need to know the wire length, panel voltage, and refer to a voltage drop chart/calculator to know if the existing wires are sufficient.

Assuming wire length of 20 feet and 5 amps at 18 volts coming out of the panel. 14 AWG results in almost a 3% voltage drop which is typically considered the the maximum drop. Lots of assumptions there so run the real numbers to be sure using a calculator such as (there are many): http://windsun.com/Hardware/Voltage_Calc.htm

I do not believe any controller can properly charge two independent batteries from one pos/neg cable. The controller needs to sense battery voltage to know "how" to charge the battery - if there are two batteries connected (not a bank), the controller will not be getting accurate information. Are you sure you do not have two 12V batteries wired together in parallel to create one 12V battery bank? (a charge controller CAN charge a bank of batteries).

[Manfred]

corvettekent wrote:
Disconnect the panels and check the voltage at the panels in the sun. If you get 0 volts then replace the panels.

I checked the voltage at the disconnected panels, no voltage. I read the specs on the controller for the old panels and it will handle the new 100W panel so I'm thinking I'm good to leave the existing 14 gauge wire in place and simply connect the new panel.

[corvettekent]

Disconnect the panels and check the voltage at the panels in the sun. If you get 0 volts then replace the panels.

[Manfred]

I noticed the controller wasn't showing the batteries charging in full sun so I tested at the battery, before the controller and finally at the panel - no power. The panels are cracked and some of the silver strips running along face of the panels are broken.

[Lwiddis]

Why do you believe the problem is the panel/panels? Test them, the controller and the wires. 14 gauge is small and depending on the distance and solar watts may well be the wrong choice. I use 10 to the combiner box and then 8 to the controller on a 300 solar watt system. 100 solar watts generally will charge a battery/ies with 100 amp hours but if you live in Oregon I'd suggest 200 watts per 100 amp hours. What have you read regarding RV solar?