Safe to charge 12v battery that is also running a fan 24/7?

Submitted by seasonedfries t3_113d7fw in DIY

Hey guys! Basically what the title says. I've got an enclosed trailer that has recently started in with a condensation problem (winter in SE Alaska) and I need to add some vents. One vent will have fans. The fans are 12v. The trailer has a small 12v battery that is used to power lights inside and I want to use it to power these fans as well.

Obviously the battery will need to be charged or it's all gonna go kaput. Instead of charging it off my running truck, I was thinking of hooking the battery up to a battery tender (or similar) to keep the battery topped up while the fans run.

I feel like this will lead to problems in the long run so I'm not sure if I should go this route.

The other options I'm tossing around is to install a shore power plug to the trailer wall (likely will be doing this regardless) and maybe get an inverter for the fans? Does that seem like the safer option?

I'm trying to do this in the most cost effective way possible. Thanks!

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Uncanevale t1_j8ppwwo wrote

You need to watch your charging voltage. With many chargers, the load of the fan will fool it into thinking the battery is depleted and raise the voltage to normal charging voltage which may cause excessive gassing and high water use. RVs get around this by having a middle charging stage where the charger operates around 13.8V when there is a small to moderate load on the system.

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seasonedfries OP t1_j8pt2gy wrote

And that's exactly what I'm trying to avoid... Damaging the battery

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Uncanevale t1_j8ptdzk wrote

Consider an RV converter as a charger, or run directly from a converter with no battery or the battery switched off.

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seasonedfries OP t1_j8pxmh0 wrote

That was a thought as well, plug a small converter into an extension cord and run the fans off it. The trailer is used for storage/workshop (in a limited capacity) and for moves. Only time I'd really NEED to run the fans is once it's parked for an extended period of time. Would look into wiring to a switch and to the battery later down the road. Would just need to figure out how to stop power from going from converter to battery, just in case it gets parked and someone bumps the switch... But that can be dealt with later

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JonJackjon t1_j8prbai wrote

Can you use a solar cell(s) to power the fan?

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seasonedfries OP t1_j8pt05i wrote

Unfortunately not... The sun here is still pretty low on the horizon and the trailer sits in the shadow of the house so it wouldn't do anything.

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SirCrankStankthe3rd t1_j8pjj6h wrote

With a tender, you'll just be running the fans off of it, and the battery will almost be moot. Except for the lights.

You'd want to make sure the charger puts more power in than the fans by a significant margin, or it'll all go kaput.

With an inverter, you'll lose quite a lot of power just having it on. Still useful

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brock_lee t1_j8psr7s wrote

Just use a charge controller, that's exactly what it does. You connect the charging source, the battery, and the load (in this case the fans) to the controller and it handles the inputs and outputs for you. They can be fairly cheap on eBay or Amazon.

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Likesdirt t1_j8q6sjn wrote

You're looking for an RV "converter" not inverter. It converts 120v AC to 12v DC for your 12v fans. Most have another wire that's set up to charge a battery.

The cheapest way is to just get a little 120v fan.

A battery tender puts out very little current, it won't keep up with any accessories. It's only meant to cover battery self discharge and a clock and radio presets.

A real battery charger will work, you can use it with the fans on, but only part time. I'm thinking the old style with a regular transformer inside, they're pretty heavy. New style switched mode might shut off when you turn something on, they're "smart" and panic easily.

An inverter will let you make 120v from a 12v battery. Wrong direction.

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seasonedfries OP t1_j8qyced wrote

The battery charger I have is an old Schumacher SC-600A. No clue where my old battery tender went

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Likesdirt t1_j8r45k9 wrote

That's new style. Will work for a topoff, try it while the fans run.

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