Using Midnite Brat to charge 12v batt from 24v Battery?

aglicknmex

Got oddball need to keep a 12v battery hot from my 24 volt solar/ battery bank.
PWM  Brat would be  fine as I have a steady 24 v source.
 Manuals on MidNite site do not make it clear if I can charge 12 from this higher voltage source?

Other suggestions appreciated.  Need at least 20 amp charging for 12 v Battery.
The brat does 30, so it is attractive!

Estragon

I'm not so sure about using a brat. You can get huge current from a battery, and I can imagine some nasty sparkiness as the pwm circuit opens and closes.

Maybe something like this?

https://www.solar-electric.com/12to24or24to.html

animatt

i have in the past successfully used morningstar 45a mppt controller.  Pv +- terminals connected to 24v battery bank. and  Battery +- terminals connected to 12 volt bank. worked well.

I had a dedicated 24v to 12v device which died. Swapped out with the backup mppt controller and was back in business.

You may want to try midnite forum to get an answer directly from them about their product.

aglicknmex

I have a large occasional load so 24-12 converter won't do.
Will check with MidNite.

mike95490

I belive the better MPPT controllers can do that, but with a PWM, you need to use a ballast resistor to limit current so you don't blow the internal fuse or MOSFET

aglicknmex

MidNite confirms what you say Mike.
Ballast resistor wastes energy...
Nice thing about a solar charger is 3 stage .

Ideas for basic mppt charger ?
It can charge 24/7 with Battery as power source, so maybe I could get by with 10amp or so. 

aglicknmex

I'm looking at Victron mppt 75/15 at 88 bucks. 
I sent a note to Peter Kennedy at PKYS  asking if it will work or burn up??
Any ideas or experience anyone??

mike95490

Morningstar solar used to have a white paper somewhere, stating that their MPPT controllers could do that, and would not void the warranty.

aglicknmex

Great info, thanks!?