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Old 11-16-2023, 09:44 AM   #1
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Charge House Batteries with Automotive Charger

Iím using my bus extensively in overcast conditions and my battery bank is suffering because thereís not enough sun to keep up with the basics. I have a DC>DC charger in the way, but in the interim, would it be OK to put an automotive battery charger on the 12v AGM bank to charge it up?

The setup I have is 600W of panel, 80A Renogy charge controller

Thanks for the help!

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Old 11-16-2023, 10:15 AM   #2
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Not a problem.
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Old 11-16-2023, 01:37 PM   #3
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Should work but keep in mind if those batteries are in a bank in parallel, it may require double the charging time for 2 batteries, 3 times for 3, etc.

Anyway, more time as there's more volume to charge up, but should work because 14v incoming is all it needs to give juice vs push juice.
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Old 11-16-2023, 01:40 PM   #4
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I'm confused,

I thought you had a 1000w renogy inverter/charger? Just feed that the 120v and it will charge the bank back up.

Or is this a different bus?

You can charge with a regular charger so long as it's a modern one with an agm setting. You run the risk of damage charging with an old unit that doesn't have the agm setting. As always, disconnect the individual batteries and isolate them from one another, charge each battery fully individually, and then reconnect. You don't want to create an unbalanced situation in the pack by charging one at at time while it's in use. Unbalanced packs can suffer damage and will have a shorter lifespan.
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Old 11-16-2023, 02:20 PM   #5
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I'm confused,

I thought you had a 1000w renogy inverter/charger?.
I HAD an inverter/charger. During a hot spell last summer it was in standby and not doing anything and then it went into alarm mode and became a screamer. I tried all kinds of things to get to to stop screaming but it never did. I assumed it was toast, yanked it from the bus and then left it to get rained on so if it wasnít bad before it is now.
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Old 11-16-2023, 02:50 PM   #6
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What volt is your panels/solar system? Maybe feed that the 12v from the battery charger and let it charge your bank correctly.
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Old 11-16-2023, 02:55 PM   #7
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What volt is your panels/solar system? Maybe feed that the 12v from the battery charger and let it charge your bank correctly.
Itís 12v.

How would I do that, pigtail off the inputs on the controller?
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Old 11-16-2023, 03:07 PM   #8
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After the first response I went ahead and connected the “dumb” charger to the battery bank and left it for a few hours then I come back and see all the “don’t do it” posts.

I got the battery up to 12.8v.

So I’ve disconnected it. I’m going to put the fridge through an AC converter and then maybe the sun “trickle charge” of 46W will be fine for the LED lighting
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Old 11-16-2023, 03:23 PM   #9
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I was reading an article that says you can do it with a “dumb” charger as long as you don’t overcharge. Does that sound right?
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Old 11-16-2023, 03:25 PM   #10
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I'd wire it parallel to the panels, and then make sure you don't exceed the input amp rating on the solar charger. I don't think it will make a difference where the 12vdc comes from, so long as you don't exceed the input ratings of the unit.

I assume your charge controller is agm friendly. That's the issue with your battery charger, is that unless it's set up to be, it's likely not. Certain agm's are very sensitive to charge rates and voltages, while others(those in start duty for instance) are much more forgiving.
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Old 11-17-2023, 08:00 AM   #11
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I was reading an article that says you can do it with a ďdumbĒ charger as long as you donít overcharge. Does that sound right?
You can, so long as watch voltage/amps like a hawk and be mindful to not overcharge. It's not so much the charger, but how it's operated/controlled.

If you're just going to leave this on a charger overnight, then it's best to hook it to your controller and let that do it correctly. An hour or so on the bank won't hurt anything, you'll likely never leave bulk stage.
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Old 11-17-2023, 09:22 AM   #12
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just buy a automatic agm charger as you can not depend on the sun
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