More data re solar panels and running the fridge on 12V - Escape Trailer Owners Community

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Old 04-17-2016, 08:48 PM   #1
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More data re solar panels and running the fridge on 12V

Today I pulled my trailer from Townsend, TN to Charleston, SC. I have 355W total of solar panels, three rooftop panels that are fixed in a flat position. As an experiment I put my fridge on twelve volts for the trip. I left at 9:00 a.m. and arrived at my destination at around 6:00 p.m. It was a sunny day. The panels were able to maintain the batteries' charge despite the drain from the fridge-- they were at 95% capacity when I arrived, down from 100% when I left Townsend.

So-- 355 watts of solar panels will keep the batteries from being depleted on a sunny day while running the fridge on 12V. In April, in the South.
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Old 04-17-2016, 08:59 PM   #2
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Start and stop time have a lot to do with it too. I only see top output for about 5 hours in the middle of the day. Chances are you are running a deficit early and late for your travel time. Having 355w you make up your early deficit during the noon hours but are left with the 5% deficit from late in the day.

I was thinking of adding another 100w for similar reasons, but running on propane is so easy I haven't.
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Old 04-17-2016, 09:04 PM   #3
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Yes, I did stop for gas. I believe that my Tacoma's alternator provides very little charging to the trailer's batteries when towing, but I haven't measured it.
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Old 04-17-2016, 09:06 PM   #4
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I assume you have dual six volts, Mike and Bob? What about adding another set of batteries vs another panel? I was thinking of getting a double set in the front box.
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Old 04-17-2016, 09:10 PM   #5
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Quote:
Originally Posted by Mike Lewis View Post
Yes, I did stop for gas. I believe that my Tacoma's alternator provides very little charging to the trailer's batteries when towing, but I haven't measured it.
Mike depending on what year your Tacoma is, if you have the tow package, it actually has an alternator with enough capacity to provide a good deal of charge to the trailer batteries. Our 2008 used to fully recharge our dual 6V whenever we would do more than a couple hours of driving.
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Old 04-17-2016, 10:13 PM   #6
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I assume you have dual six volts, Mike and Bob? What about adding another set of batteries vs another panel? I was thinking of getting a double set in the front box.
Four 6-volt batteries weigh 240 lbs. Front box on my 21 has a sticker that says "Do Not Exceed 100 LBS.".
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Old 04-18-2016, 01:11 AM   #7
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I think just about any vehicle capable of towing a trailer and built in the last decade or two has more than enough alternator capacity to power the refrigerator and add some charge to the battery... but the alternator doesn't run at full capacity because the correct voltage at the truck's battery is too little at the other end of the long wire to the trailer. This is highly dependent on wiring details.

Apparently some vehicles boost their voltage setting to a higher level when in tow-haul mode - or at least doesn't drop the voltage to help fuel economy - and that would help. Maybe some Toyota models and years keep the voltage up - mine doesn't have a tow-haul mode but it's not a truck.

The solar panels have two advantages over the tow vehicle's alternator: the panels are more directly connected to loads in the trailer; and in full sun their open-circuit voltage is much higher than any 12V vehicle's voltage regulator setting.
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Old 04-18-2016, 01:47 AM   #8
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The solar panels have two advantages over the tow vehicle's alternator: the panels are more directly connected to loads in the trailer; and in full sun their open-circuit voltage is much higher than any 12V vehicle's voltage regulator setting.
All good points and consider this:

The TV alternator 'looks' at voltage and the solar array 'presents' a higher voltage. But the flat mounted panels can't produce anywhere near the load of the refrigerator.

So the alternator 'sees' a higher voltage on the battery wiring circuit ... and assumes all is well. In this case (refrigerator on DC) the result is undercharged batteries.
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Old 04-18-2016, 08:29 AM   #9
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The combined length of my Tacoma + Escape 21 is 39 feet, one inch. The truck's alternator is in the front and the trailer's dual six-volt batteries are in the back. This is why I assumed the alternator has little effect charging the batteries. Someday I'll get a friend to watch the trailer's battery monitor while I rev the truck's engine to highway speeds. On a sunny day, of course, to get the influence of the panels as well.
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Old 04-18-2016, 09:02 AM   #10
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Doesn't it also depend upon the thickness of the wire from the alternator to the trailer? I seem to remember reading a thread about that, smacking my head, and saying 'Duh, another thing I should have done...'
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