I have an old truck and I don't drive it much. I've hooked up a 1.5v solar charger to the battery to keep it fresh. It's working well, but when I do drive it I need to unplug the solar panel or risk burning it up when the truck is running. My worry is when someone borrows the truck that they'll forget the panel and maybe start a fire in the cab.

My question is what switch would I need to be able to toggle the solar panel ON and the truck ignition OFF or have the solar panel OFF and the ignition ON? I.E. - flip it up and the panel starts flowing juice to the battery and you can't crank the truck. Flip it down and the solar panel's path to the battery is severed and the truck will crank if you want to.

I've looked at the on/off/on switches on Amazon and, at least the ones I've found, don't seem to do what I want. They seem to just turn the same thing on when flipped up or down? Example with a wiring diagram here: https://www.amazon.com/Nilight-Heavy-Duty-Toggle-Switch/dp/B0002ZPBRA/ref=sr_1_1?keywords=on+off+on+switch&qid=1580181117&s=automotive&sr=1-1



I would look into setting up a relay controlled by the ACC or RUN circuit. When the coil in the relay is not energized the contacts would connect the panel to the battery but when you switch the ignition on or to acc it would energize the coil and open the connection.

Typical 5 pin auto relay would look like below:

  • 86 : ACC/ON
  • 85 : GND
  • 30 : BATTERY
  • 87 : NO CONNECT
  • 87A : Solar Panel



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  • so 86 needs to go to a wire that turns hot when the truck is turned to acc (or on)? Would the cigarette lighter wire work for that? On 85, just use the cigarette ground? After that, I guess that I cut the solar panel hot wire and the battery side goes to 30 and the solar panel side goes to 87A? Do I leave the solar panel ground wire as is (uncut)? – Dropbear Jan 28 at 4:26
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    Like this? i.imgur.com/rJFMycr.png – Dropbear Jan 28 at 4:40
  • Yes, like that. Cig lighter is good if yours is on acc/run circuit. – narkeleptk Jan 28 at 4:42
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    I'm not sure why it will blow the panel, but the warnings on the package were to never have it hooked up when the vehicle was running. I like this solution - it's relatively cheap and doesn't require any user interaction. I'm going to grab a few of these relays on Amazon and give this a shot. amzn.to/2GvE4bS I really appreciate the help at this late hour. – Dropbear Jan 28 at 5:04
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    Nice diagram!!! – Moab Jan 28 at 17:47

You can't bolt a raw panel to a car battery, you need some sort of charge controller. But don't overthink it. If your solar charger is any kind of quality, you really don't need to worry about it.

  • When the engine is cranking, the solar charger will "try to help", but its current is limited by panel output.
  • When the engine is running, the alternator will be putting out the same "top up the battery" voltage as the solar charger, and no current will flow.

I wouldn't worry about it unless you have had problems, in which case I'd look at quality. Try a Morningstar Sunguard.

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