Charging 12 volt battery from a larger 12volt battery

[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.

[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

[Mike90250]

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

[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!

[Raypat]

I will post results after I build it.

[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.

[AzRoute66]

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

[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]

If the Load terminals of the charge controller will provide enough amperage, and is smart enough to do a low voltage disconnect, I don't see why not. The risk of connecting it directly to your big battery is very minimal though, once the smaller battery is charged the current drawn by the charger should be minimal.

[Raypat]

OK Thanks Neo we finally got there. That is what I will do. I get it now that the second pwm charge controller was a bad idea and all I need is one of those with a DC-to-DC Battery-to-Battery Charger. The last piece of the puzzle for me is this. Can I connect the DC-to-DC Battery-to-Battery Charger to the load terminal of the solar charge controller to protect the big battery from over discharging which would be unlikely anyway or do I need to go direct to the big battery?

[NEOH]

Hi Raj, Yes I could do as you suggest and spend um I dunno but it sounds like plenty. Or I could just buy a charger like the one Neo has suggested. No boost converter needed so I guess I avoid the problem mentioned by Mike and Bcroe. If I understand correctly I should be able to connect that charger direct to the load terminal of the charge controller and be good to go. The charger will handle the voltage boost as well as the correct charge cycle ending in a float charge for the glider batteries. Am I right in my assumptions here or will the charger and the Charge controller not get along? Thanks again to all who have replied.

Do not attempt what Raj suggests in message #23 - bad idea.

You are on the right track by using ...

A) PV Charge Controller to the main battery bank and then use a DC-to-DC Battery-to-Battery Charger to recharge the small 7AH battery
This method will recharge the small 7AH during the night, so the 7AH battery will be ready to use first thing in the morning.

B) A Dual Battery Solar Charge Controller method
The problem with the Dual Battery Solar Charge Controller is ... it only recharges the small 7 AH during the daytime on sunny days - but that is when you actually need to use the 7 AH battery.

[Raj]

any PWM controller will last about 1 second before it blows out, PWM cannot protect itself. You have to use a MPPT controller, rated to work with batteries, in addition to solar sources. (Morningstar MPPT gear is approved for this use)

Thanks Mike, I forgot that the controller charging the 12V bank needs to be MPPT.

[Mike90250]

......., then connect a 12 volt PWM controller between 24V bank and the 12V glider batteries for charging.

any PWM controller will last about 1 second before it blows out, PWM cannot protect itself. You have to use a MPPT controller, rated to work with batteries, in addition to solar sources. (Morningstar MPPT gear is approved for this use)

[Suprasoup]

Raypat ,

Yes, you can charge your 7 AH 12 volt batteries from a 60 AH 12 volt battery.

All you need is something like this ...
https://www.amazon.com/OptiMATE-TM-5.../dp/B011J76CFE

I am not recommending that particular model.

If you do not understand the PV Solar Panel stuff,
then just buy a kit containing the 200 Watt Solar Panel & 12 Volt Charge Controller.

Like this ...
https://www.ebay.com/itm/160-Watt-Of...kAAOSwHsRYCDGF


Buy the 60AH Deep Cycle battery from Walmart
$80 = Marine Deep Cycle Group 24DC
$90 = Marine Deep Cycle Group 27DC

He could use a hobbyist charger like this...

https://www.amazon.com/dp/B01HXHGARY/ref=dp_cerb_2

almost all of them have settings for lead acid batteries. I personally use a Hyperion eos0606i. I use it to charge HT radio batteries when out in the field. Whether it

[Raypat]

Hi Raj, Yes I could do as you suggest and spend um I dunno but it sounds like plenty. Or I could just buy a charger like the one Neo has suggested. No boost converter needed so I guess I avoid the problem mentioned by Mike and Bcroe. If I understand correctly I should be able to connect that charger direct to the load terminal of the charge controller and be good to go. The charger will handle the voltage boost as well as the correct charge cycle ending in a float charge for the glider batteries. Am I right in my assumptions here or will the charger and the Charge controller not get along? Thanks again to all who have replied.