24v battery to power charge controller 12v battery.

[CUBBYBOY57]

I have a 24v system LV2424 and 230Ah battery.
I am cooling a shed (Texas) with it.
My battery gets full mid day on sunny days.
I use a 12v inverter and battery to battery backup a fridge. Manual transfer switch. Can I recharge the 12v battery with a charge controller input by the 24v battery?

Is it better to power a 120v charger through the LV2424?

LV 2424 can't take the ac and fridge cycling at the same time.

Thanks for any input.

 

[sunshine_eggo]

Battery input into a MPPT can be done, but it's kinda pointless. The MPPT can't engage its algorithm, and it has to be fused between 24V battery and mppt.

While you're looking at only about 75% efficient (24VDC to 120VAC to 12VDC conversions), I would prefer an AC powered charger.

Alternatively, this unit:

Amazon.com

Takes wide input voltage (19-36V) and converts to 13.8V @ 40A. 13.8V isn't an optimal charge voltage, but it's a great float voltage, and it can bring batteries to full charge over 24+ hours of charging. If the 24V kept the 12V floated at 13.8V continuously, it would remain fully charged and available for backup. You could eliminate the transfer switch. Simply run the fridge off the 12V inverter continuously while the 24V system keeps the 12V floated at 13.8V. If the 24V system goes down, it simply just keeps running off 12V.

 

[CUBBYBOY57]

Thanks for the reply - I was thinking of the buck converter, but thought a PWM controller would do a better job of charging. Just wanting to shut down the LV2424 when solar isnt producing and already have 12v system backup from a "portable" camping setup I built. The battery/inverter acts like a giant soft start to the load the fridge puts on when it starts it is fairly low power so don't need a ton of input overnight.
I think I will stick with the 120v as I can put 40-50 AH in the 2-2.5 hrs of excess sun - If the power is out longer than 2 days I have more problems than my system can handle.

 

[sunshine_eggo]

Thanks for the reply - I was thinking of the buck converter, but thought a PWM controller would do a better job of charging. Just wanting to shut down the LV2424 when solar isnt producing and already have 12v system backup from a "portable" camping setup I built. The battery/inverter acts like a giant soft start to the load the fridge puts on when it starts it is fairly low power so don't need a ton of input overnight.
I think I will stick with the 120v as I can put 40-50 AH in the 2-2.5 hrs of excess sun - If the power is out longer than 2 days I have more problems than my system can handle.

PWM controller is an absolute no-go and a fantastic way to destroy itself and possibly the other things. PWM work by shorting the PV to battery, so it would try to short your 24V battery to your 12V battery.

 

[CUBBYBOY57]

Thank you! Will stick to what I have.