Hello, Our 2006 23C Classic came with a “Sunsei Solar Charger 1200” (solar panel) with 15V “operating voltage”(18W) 1200mA. Also installed was a Sunsei Charge Controller. I assume these were installed by the manufacturer but am not sure. Regardless, I replaced that original panel (it was cracked) with three Harbor Freight 15-W (14.5 v) panels (maybe 10 years old, still in the box, never used), whose wires I spiced together to one output jack (repurposed from the old panel). I recall the combined output was about 21 v measured at the output jack. I plugged that jack into the trailer input wire jack on the roof. The controller light lit green and its output was around 13v. Recently, while boondocking under the bright sun of the Mojave Desert, when I checked, everything seemed to still be working well but for some reason when I checked later on the controller output dropped to about 5v and the controller light was dark (unlit). I checked and the solar panels’ output was still about 21v.
So, I am wondering whether the charge controller simply “burned out” (does that happen?) or the gauge of the wire for the original panel extending through the roof and through the trailer and eventually wiring to the controller is now the wrong size for the “new” panels. I assume the charge controller is about 18 years old. Also, before considering getting new 100W panels, would I need to replace the old wire with new wire of a different gauge?

I will let the experts in this area (and forum) give you the right answers to your questions, but if I remember right the wires running from the original roof panel all the way to the fridge area where my controller was located was 12 gauge wire. I believe for most systems 10 gauge is minimum size wire to be considered. Also, when upgrading your panels, especially moving to 100W and larger, you will want/need to upgrade your controller. The old Sunsei was good 20 years ago for trickle charging your batteries but that was about it.
I know the experts will be chiming in soon to give you great advice, and possibly correcting me in the process.

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2007 2307C Classic
2007 2500HD 4x4 GMC

I'm not an "expert" but I agree with Rahn about the wire size. I HAVE installed solar battery charging on my trailer so I've learned a few things.

First, from your post, you connected the new panels in parallel, since the new, no load voltage was around 21V. This means the combined Amperage of those panels could be as much as approximately 3 Amps (which is easily 3 times the amperage of your old "toy" panel). I think you DO need at least 10 gauge wire to carry that Amperage and the combined Wattage (3 x 15 = 45) may well be too much for the original "toy" controller. You're seeing me casting disparaging descriptions of the original panel-controller setup, because I think they were mostly cosmetic.

From your post, it sounds like you've fried the controller and you should replace it with one that can support over 45 Watts (I'd shoot for 100 if you're going to retain those panels). In addition, I'd connect each of those panels to each other in SERIES, which will up the voltage (possibly to around 63V, no load) but will keep the Amperage at around 1 Amp max. This will allow you to use the smaller wire that is installed. Make sure any controller you get will handle the 63 V input. It will reduce that voltage to a safe battery voltage (around 14+ V), while increasing the charging Amps to 3 times that of a single panel.

If you keep the panels connected in parallel, then you SHOULD increase the wire gauge from them to the controller. 10 gauge should work, since you don't have a high Wattage solar array.

- Jack

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Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH, Progressive Dynamics Converter, Fan-Tastic Fan, LiFePO4 battery 12V DC Electrical System, SoftStartRV mounted on A/C
2024 F150 Platinum FX4 3.5L PowerBoost SCrew

Rahn and Jack, Thanks very much for your replies. You of course correctly inferred I wired the panels in parallel. I frankly do not recall why but regardless I agree the originally installed set up was mostly “cosmetic”. It must have seemed kind of neat back in 2006. Seems my easiest option would be to 1) rewire the panels in series, which would seem to obviate the need to replace all of the wiring between the panels (not mounted) and the converter location (currently in the paneled exterior space behind the refrigerator), and 2) get a new converter that in the (near?) future could handle at least a 100 W panel. I might want to move its location to inside somewhere as there is not much room where existing converter is.
I really appreciate your help and think this HiLo Trailer Forum is invaluable.
Bill
Eureka CA

I am an expert.
Sounds like you need help. If and when the batteries are charged then the controller will not put out much voltage. It might put out zero. When batteries are depleted then the controller will put out its full capacity.
However, it should not put out 5 volts. Are you sure about this 5 volts? ON a 12 volt system you should never see 5 volts.
btw, yes your panels will always put out more voltage than your battery is rated at. A typical 100w panel will put out 18 volts and is intended for a "12" volt system. Lead Acid batteries at 13.6 volts and lithium at 13.6 or slightly higher. Batteries can be charged at 14 volts, as your car alternator does, or can be maintained (float) at 13.6.
Always and only run your solar panels through a charge controller to the batts, NEVER connect directly to the batt.
You have almost silly small solar panels. These are good for winter storage to just keep batteries from naturally losing power.
Get 100-200 watts of solar at least if you going to waste time messing with it. The dealers put this garbage on the roof bc consumers are pretty uneducated and think a 20 watt panel counts as "solar". It does not. Throw that junk in trash.

Controllers are rated by amps, not so much watts. Get a 20 amp at minimum, but a 30 is better to future proof camper.
Look at EPever for good price and quality.

Yes, you can run in series. 2x100 watt panels could give 24 volts (37 actual volts off panels), and the controller will make that work for your 12v system.

Always connect panels last, and disconnect panels first.

Your issues prob not wire size related, but since the manufacturer was making wire decisions then is good bet it is the wrong size for anything. Run new wire.
Do NOT use the chassis for ground between panel and controller and battery. Run two wires, pos and neg.

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1997 22L
Renovation complete!