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Old 12-29-2015, 10:56 AM   #1
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20w solar charger

I purchased a 20w solar battery charger thinking that it would not overcharge like the onboard converter is accused of. I checked the voltage with a multimeter and it was as 17.5v. The internet information says the output is up to 21v. Without getting into a lot of electrical theory, are these high voltages doing the same?

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Old 12-29-2015, 01:19 PM   #2
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Directly output from the solar panel that's pretty normal voltage. You need to put a solar charge controller between the solar panel and 12v system in the trailer. It steps down the voltage from the panel to the necessary voltage for 12v load and battery charging. Since it's just a 20w panel you'll be able to get a basic one fairly cheap.

Just reread, is it a integrated all in one solar battery charger and not just a solar panel. If so that may be normal for its operation when not connected to a battery. Indicating a no load voltage output. Connect to battery and see how it functions once the battery is fully charged.

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Old 12-29-2015, 01:22 PM   #3
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The voltage you measured is the open circuit voltage. When attached to a battery it will drop much closer to the battery voltage, even with no charge controller (which in reality you should have anyway).

A 20 watt panel will produce so little output that you probably will never have a situation where you overcharge the battery anyway. Slightly over an amp of charge current max, a few hours a day in unlikely to cause you any issues.
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