12V battery charger question for the experts

[someotherguy]

I've got a small sealed lead-acid 12V 1.3Ah battery I need to frequently keep charged (wireless tow lights), and I have some problems to solve around that.

1. The charge cord for the battery is "dumb" and just a simple lighter socket plug-in. If you follow the manufacturer's advice of "you can leave it plugged in all the time" you will kill the battery by over-charging it. Seen it happen many times, you'll leave it plugged in because you forget to unplug it.. boom, seriously shortened battery life.

2. I'd like to source an automatic charger that actually does what it claims. It seems the Battery Tender type stuff still just boils people's batteries to death. The charge cord plugs into a small socket on the bottom of the tow light housing. Whatever suitable charger I might find, I'd just hardwire the output to that charge cord end, and hardwire the input side of the charger to a 12V supply in my truck. There's all kinds of 120V->12V stuff that claims to do this (Battery Tender, Noco Genius, etc.) but I need a 12V->12V solution so it can live in my truck.

The batteries:

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Any ideas? Thanks!

Richard

 

[Ruff Idol]

How about a 24V HVAC timer relay like what is inside an air handler? I can imagine it probably works about the same with 12V, or you can get one that explicity takes 12v. It would certainly be a lot less likely to overcharge the battery with something like that, although risk not completely mitigated.

 

[618 Syndicate]

Does the truck live outside? I have a Bezos special solar float charger that I use on my square dually, have had it for a couple of years now. No issues at all.

 

[RichLo]

Since its 12v-12v, how about a timer for the dumb charger? 15 min on, 15 min off or 30 min off to let it cool down and not boil to death. Those little batteries should be fine with the 14.7v alternator but just not for a full 12hr shift plugged in without an auxiliary load like big car batteries have.

Or thinking about this more... hard wire the big battery to the little ones in parallel so the little ones see the same draw as the big one, running radio, lights, winches, etc. That dumb charger probably has a 1-way check valve (Diode) that keeps them from draining and that's what boils them. Just gotta figure out an automatic cutoff switch for when you shut down they wont stay connected and drain each other when parked.

 

[someotherguy]

I should probably clarify. I need to charge the battery usually once a week, and I do so when my personal truck is sitting in the driveway not being driven. My regular routine is to charge it approx 10-12 hours and unplug it. Sometimes I forget to unplug it and it stays on the cord for 2-3 days.

Richard

 

[someotherguy]

I use 0.6A 12V tenders sold by Yuasa.

I've monitored them with a DVM and they float practically forever at 13.6V.

On initial turn-on, they'll "charge" until the battery voltage reaches 14.4 or so, then they'll back down to 13.6 and float for something like a week, then they'll repeat the 14.4V session and back to float.

I've been happy with them, been using them for 20+ years on motorcycle and automotive batteries.

These are a 120VAC->12VDC tender though, yeah? I'm really hoping to find something that is 12VDC->12VDC though it may not exist.

Richard

 

[1998_K1500_Sub]

These are a 120VAC->12VDC tender though, yeah? I'm really hoping to find something that is 12VDC->12VDC though it may not exist.

Richard

Yeah... I just read your post thoroughly and realized my error, so I deleted my post. Then I saw this one from you. Oh well, I messed-up all-around.

 

[Orpedcrow]

There oughta be some kind of dc-dc 12v battery charger for RVs

 

[Orpedcrow]

Orion-Tr Smart DC-DC Charger Isolated - Victron Energy

The Orion-Tr Smart DC-DC charger is a professional DC to DC adaptive 3-stage charger with built-in Bluetooth. For use in dual battery systems in...

www.victronenergy.com

Something like this or there’s another company called Redarc that’s popular among overlanders and other people that require dual isolated batteries

 

[someotherguy]

How about a 24V HVAC timer relay like what is inside an air handler? I can imagine it probably works about the same with 12V, or you can get one that explicity takes 12v. It would certainly be a lot less likely to overcharge the battery with something like that, although risk not completely mitigated.

Interesting idea.. a timer would kinda work, but the ultimate solution would be an effective maintainer-type charger that would shut off "smart" so the battery gets a proper charge each time. The discharge rate is not constant, so I might wrap up my work week with the battery in a slightly different state of discharge each time.

Does the truck live outside? I have a Bezos special solar float charger that I use on my square dually, have had it for a couple of years now. No issues at all.

Not a bad solution, but don't really wanna have to mess with putting the solar charger up, then taking it down, when I go to drive the truck next. Plus if it rains, wires gapping the weatherstrip usually leak inside. I've had it happen even with a really thin GPS antenna wire.

Since its 12v-12v, how about a timer for the dumb charger? 15 min on, 15 min off or 30 min off to let it cool down and not boil to death. Those little batteries should be fine with the 14.7v alternator but just not for a full 12hr shift plugged in without an auxiliary load like big car batteries have.

Or thinking about this more... hard wire the big battery to the little ones in parallel so the little ones see the same draw as the big one, running radio, lights, winches, etc. That dumb charger probably has a 1-way check valve (Diode) that keeps them from draining and that's what boils them. Just gotta figure out an automatic cutoff switch for when you shut down they wont stay connected and drain each other when parked.

You just touched on something I hadn't really thought through. I don't believe the charger has any kind of diode in there because if it loses input power for any reason - lighter socket fuse pops, charger fuse pops, crummy connection in the lighter socket.. and the battery still has any charge left, it will light that LED up on the charger as if it's working. Then you go to grab the lights and they're near dead. Frustrating. So to me, it seems like the charger is just a dumb interface - an adapter - for the lighter socket to the tow lights.

One would THINK that leaving it plugged in 24-7 would be "OK" as the batteries should just equalize, yeah? The big battery in the truck charges up the little battery in the tow lights. Maybe I'm misunderstanding something about how that works.

Yeah... I just read your post thoroughly and realized my error, so I deleted my post. Then I saw this one from you. Oh well, I messed-up all-around.

No worries! It's a weird situation and kind of an oddball request.

There oughta be some kind of dc-dc 12v battery charger for RVs

Thanks, I'm looking up anything I can find and search terms make it tricky, since practically everything that comes back is a 12V battery charger, yeah, but has 120V input.

Richard