Charging 12 volt battery from a larger 12volt battery

[Raypat]

Thanks AZ. I think I can go ahead now and build this system. If the charge controller does not like the DC/DV charger I am happy with going straight off the big battery. Thanks to all that replied.

[AzRoute66]

Make sure you head back with the 'as built' specs and let us know how well it is working for you.

[Higher Voltage]

I think your best with a small inverter set up and a battery 120v battery charger. You also want to run lights and a soldering iron.

[Raypat]

I will post results after I build it.

[PNjunction]

Ray - for your application, the tecmate-optimate dc-dc charger does a great job. I use one often to keep a remote industrial vehicle topped off from a larger battery that I hump out to the field.

https://tecmate.com/products/tm500/

It's smart for both the target and source battery. And at only 2A, will do a great job of normal charging a 14ah agm battery. Because the absorb stage is not just pure CV, but a pulse/test type of absorb, it helps bring up lagging cells without overcharging the high ones.

If I want to be a purist, I'll take my much larger solar charged agm out there, and let the Optimate do it's thing. Then I can claim that the tractor is being maintained by solar, without having any panels in place!

[Mike90250]

New, related question - any leads on a AGM charger that can run off a vehicle alternator (while the vehicle runs its flooded battery) ?

[bcroe]

New, related question - any leads on a AGM charger that can run off
a vehicle alternator (while the vehicle runs its flooded battery) ?

Your alt V is clamped by the flooded battery, but you could get one of those boost buck 12V
converters to put the voltage where you need it. For isolation, add 3 more big diodes (half
a bridge) from the alt winding to the new 12V circuit. Bruce Roe

[TommyDre]

Could a solo 12 volt battery be connected via auto jumper cables to batteries being charged by a small solar array during daylight hours? Just wondering since I just started doing this last week and it seems to be working. These used SLA batteries haven't died yet, they keep the pig behind her electric fence and charge the small AA, AAA, and D batteries.