“Solar Panel” switch on Systems Monitor

Hi all, [I am reposting this as I think I posted in the wrong place] Our 2007 23C “Classic” had a 18W solar panel, which I removed as it was broken. I replaced the broken panel with a set of three 15W panels (because they were free, never been used and that’s all I need for our purposes). The “Systems Monitor” panel mounted to the side of the refrigerator includes a toggle (?) switch labeled, “Solar Panel”. I do not know what this is for. Do you switch it on when the solar panel(s) is (are) charging? A related question: Does the three-setting black switch near the door entrance near the floor (for the cable system, off and 12-volt on) need to be “on” for the the solar panel to work (i.e. act as a source of power)? Thank you for your help with this.

I THINK the original solar panel you removed was actually a 15 Watt panel, but the difference is inconsequential. My only concern now, is that you have a 45 Watt panel source and that MAY overload the "toy" PWM charging controller that the HiLo factory installed.

On a "good" day, you will probably see only about half of the rated 45 Watts from the panels into the controller. At 14V (a typical charging voltage) this means the controller would have to handle about 1.6 Amps. If the controller can handle that, you're OK

I would guess that the black 3 - position switch (the Master switch) is not part of the solar charging circuit, but you can test this by putting the trailer in sunlight, and not plugged into shore power or the tow vehicle's charging circuit. If you read somewhere around 14V on the battery terminals, you are receiving charging current. If the voltage is 12.7V or less, the battery is not being charged.

I would also guess that the other switch labeled "Solar Power" DOES have to be on if the battery is to receive solar charging power. Test this using the procedure I described above. I suspect this switch is there to allow you to disconnect the solar panels from the battery to prevent overcharging.

It's POSSIBLE you have NO solar charging controller though, and if that is the case, I'd get one and put it in the circuit to prevent damaging voltage to the battery. Usually, a controller will reduce the charging voltage when the battery is full, to prevent overcharging.

- Jack.

JackandJanet said:

I THINK the original solar panel you removed was actually a 15 Watt panel, but the difference is inconsequential. My only concern now, is that you have a 45 Watt panel source and that MAY overload the "toy" PWM charging controller that the HiLo factory installed.

On a "good" day, you will probably see only about half of the rated 45 Watts from the panels into the controller. At 14V (a typical charging voltage) this means the controller would have to handle about 1.6 Amps. If the controller can handle that, you're OK

I would guess that the black 3 - position switch (the Master switch) is not part of the solar charging circuit, but you can test this by putting the trailer in sunlight, and not plugged into shore power or the tow vehicle's charging circuit. If you read somewhere around 14V on the battery terminals, you are receiving charging current. If the voltage is 12.7V or less, the battery is not being charged.

I would also guess that the other switch labeled "Solar Power" DOES have to be on if the battery is to receive solar charging power. Test this using the procedure I described above. I suspect this switch is there to allow you to disconnect the solar panels from the battery to prevent overcharging.

It's POSSIBLE you have NO solar charging controller though, and if that is the case, I'd get one and put it in the circuit to prevent damaging voltage to the battery. Usually, a controller will reduce the charging voltage when the battery is full, to prevent overcharging.

- Jack.

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Hi Jack,
Thank you for your reply and help with my questions. I regret my delay in getting back to you.
You are right, it was a 15-W panel.
I set up the three 15W panels originally from Harbor Freight in parallel. Their “nominal” voltage is 14.5 V. I think that means they each produce at most 15W / 14.5 V = about 1 Amp or the three combined, 3.1 Amps. The factory installed controller (Sunsei Charge Controller CC10000) can handle 10 Amps, so I think we’re good.
By the way, if I ever want to upgrade to AC power using (e.g.) 400Ws and an inverter, I would need a new controller but I wonder whether the factory installed wire extending from the panels through the roof to the controller would have a large enough gage (“thickness”) to handle it.
A while ago, I used a multimeter on the controller to check the voltage coming in from the panels and what was going to the batteries up front. I assume the multimeter reading on the controller leads from which the wires to the batteries extend is what is coming out of the controller and not a reading of the batteries. The voltage from the panels was (as I recall) a maximum of 14 V but of course varied a lot depending on how the panels were situated, time of day and so forth. The reading at the leads on the controller with the wires going to the batteries (I think/recall) was at most 12.7 V.
I will carry out the tests as you describe when we are back to where our HiLo is currently set up. Your approach makes sense. I now speculate that the solar switch on the monitor panel when “on” might direct the voltage from the panels directly to the DC appliances after passing through the controller (and not sending the voltage to the batteries) but the results of the tests you describe will tell. Thanks again, Jack.
Bill

Great, Bill! The "resting" voltage of a lead-acid battery (no load, no charging, and this way for a few hours to dissipate any "surface charge" or "surface drain" from a load) is 12.7V for a new, fully charged battery. Anything above this means it is getting a charge and anything below means it is either somewhat discharged or is supplying a load.

I've found, and this is supported by what I've read, that solar panels can almost NEVER deliver more than half their "rated" Wattage, so your 45 Watt panel setup would probably never give you more than 1.6 Amps. I've seen a maximum of 11 Amps from my 300 Watt solar panels, not the 21 Amps that 300 Watts at 14V would deliver.

You need fairly large wire to carry the Amperage that solar panels can deliver. I use 10 gauge wire on mine and, if you think you might upgrade in the future, that would be a good size for you. However, for the Amperage your panels deliver, 14 gauge or even 16 gauge would work fine. (Larger numbers are smaller wire as you probably know).

It IS possible that the solar switch behaves as you described, but I suspect it simply disconnects the panels from the battery. If it is connected to the DC circuits in any way, it would be charging the battery too, unless the battery were disconnected from the DC circuits.

- Jack