Using solar panel to run frig while enroute?

[B_and_D]

I'm thinking about using our portable, folding solar panel to run the refrigerator while we travel to our destinations. We'd open it up and put it in the bed of the pickup (somehow secured) and run a wire to ?

I'm thinking it's probably not a good idea to run the wire to the main battery as it will also be connected to the truck and charging through the Bargeman connector.

Any thoughts on this?

Thanks

D

[Craigrrr]

Connecting to the battery on the TM is how I would do it, just make sure your solar panel has a charge controller on it so it does not over charge is all. It will cut off if the battery has enough charge so no problems I see.

[Bill]

Remember that the refrig eats about 120-150 watts, so you will need that much power from the solar setup if the truck connection won't charge. How much power does your folding panel produce?

I tend to agree with Craig about keeping the solar panel connected to the battery. If the solar drops out (shadows, clouds, trees, etc), the battery and the truck's charge line can pick up the slack. And if the battery voltage drops too low, both the solar and the truck can contribute to the charge. (I think that's right, but I will defer to the experts.)

Remember also that the solar panel itself doesn't put out a regulated voltage. It can be as high as 21 volts when no current is being drawn, but will dip to some lower (and uncontrolled) voltage as the refrig draws current. It is the battery that tells the controller how to regulate the voltage.

Also, don't forget to turn on the refrig vent fan as you close down to hit the road.

Bill

[B_and_D]

Thanks for the replies...it's a 100W panel (2x50) and it does have a charge controller, its size is geared to just the two panels. It does a great job of charging up our auxiliary 12V battery in full sun. The truck charges up the batteries as we drive but if we run the refrigerator seems like it barely keeps up. When we get the truck out of the barn next time I would like to measure the amps that are coming out of the Bargeman plug.

[rickst29]

Power to run the fridge will be drawn from the "most attractive" of Voltage sources. The following background information is important, and deserves a post of it's own:

In normal TM operation on the road, the "12V" battery charge of the TV actually offers about 13.5V It's controlled by by the alternator (2 wire alternators) or an interconnected ECM (3 wire alternators, used in Subaru and etc.) The TM batteries offer only 12.8V (fully charged) while being discharged. But a problem happens immediately, as current begins to be drawn through the Bargman: The "power loss" increases with current, and much longer wire lengths (with more resistance) are involved in the TV "power source path".

Inside the TM, there is a #10 wire from the end of the Bargman (behind the fridge) to the load center. This competes with the wire from the TM battery string into the load center - whichever is longer loses the battle, with higher resistance.

But the next long segment is a problem only for the TV path: the Bargman cable itself, including length inside the TM and outside on the hitch, along with any "extra" length which is looped up in towing.

Finally, on the path to the TV Fuse box and 12V bus, we have the most important wire in the equation: The wires inside the TV itself, FROM the "Trailer Battery" fuse into the Trailer connector, and along the body from the under-dashboard trailer connector to the Bargman. Nearly every vehicle manufacturer makes this wire tiny, using "chassis wiring" rules instead of NEC "home wiring" rules.

Do not underestimate the damage of that last wire, within the TV! In my 2007 Toyota 4R, it was definitely #14 or smaller, even though the fuse allowed 30A. When you try and pull 10A through that wire, to run the Fridge, your 13.5V is dropped to 13.1V (or worse) at the TV connector. Lose another 0.3V in the Bargman cable, and cable-end to load-center wire segments, and the trailer battery becomes the more attractive power source.

In "typical" configurations, the TM house batteries will be drawn down to about 60% SOC before a majority of Fridge power requirements begin to be drawn from the TV.

[tentcamper]

we went a different way. We isolated the camper batteries from the camper 12V buss in the converter via a switch at the battery. When the switch is off the only source for 12V to the fridge is from the TV via the 7 pin connector. It works very good fridge stays cold and batteries are topped off or the same level as they were when we left.

We also need to re-wire the brake breakaway switch 12V source directly to the battery from the 12v buss in the converter to ensure the switch was operational with the switch off.

Only down side we have found is when we do leave a cs without 120V and batteries are low and we are traveling to a CS without power. We have to turn on the switch to get some recharging while traveling. But it's issues as factory wiring.

PS: I ran 2 - #12 wires from the tv battery to the 7 pin connector and grounded the connector in 3 different places on the tv.

[BrucePerens]

I suspect that a 100 to 200 watt solar panel might not be much help if positioned in the pickup bed while moving. They are only going to put out their full power in optimal conditions, and work very poorly if they are partially shadowed. Like at 10% of their rated power, no kidding. I stuck 400 watts of panel on top of my camper with the assumption of reliably getting 100 watts. In a shaded campsite, I get less than that.