48v Stepdown to 12v and charge a lead-acid battery?

[Riley]

Hi, I have my RV's existing system using a 12v system, so I would need to connect my 48v battery bank to provide power for 12v systems, but one of which is an RV generator, it needs maybe 300CCA to start, so it seems I need some 12v lead acid battery in between, can I use a 48v stepdown convertor connect from 48v battery to a 12v lead-acid battery, and it will charge and maintain it? Will my step-down converter limit amperage by itself?

the converter I am using is "DC Voltage Regulator Buck Converter DC 48V Step Down to 12V 30A 360W Reducer"

 

[sunshine_eggo]

A 12V lead-acid battery sitting at 12V is in bad shape - likely < 50% charged and being murdered.

Some of the converters will output 13.8V, which is a good float voltage that will keep a battery fully charged:

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Accepts 38-60V in and outputs 13.8V

The converter will only output a maximum of 30A. The act of starting might pull the voltage low enough that it trips the low voltage protection, but it will either reset itself, or you can power cycle it to restore it.

 

[Joe BoyKey]

Have this tied to my 51.2v Lifepo4 Batteries, it keeps my 12v agm system at 12.3 if it gets low, Joe.

 

[John Frum]

Hi, I have my RV's existing system using a 12v system, so I would need to connect my 48v battery bank to provide power for 12v systems, but one of which is an RV generator, it needs maybe 300CCA to start, so it seems I need some 12v lead acid battery in between, can I use a 48v stepdown convertor connect from 48v battery to a 12v lead-acid battery, and it will charge and maintain it? Will my step-down converter limit amperage by itself?

the converter I am using is "DC Voltage Regulator Buck Converter DC 48V Step Down to 12V 30A 360W Reducer"

Your RV probably has an ac2dc converter to power the 12 volt system from shore power.
Depending on the size of your 48 volt system and the voltage that the ac2dc converter provides you might use that to keep your lead acid battery charged.
Those ac2dc converters are pretty inefficient but it should work.

 

[sunshine_eggo]

Your inverter probably has an ac2dc converter to power the 12 volt system from shore power.
Depending on the size of your 48 volt system and the voltage that the ac2dc converter provides you might use that to keep your lead acid battery charged.
Those ac2dc converters are pretty inefficient but it should work.

I think you meant to say "RV"?

Very good point and not even on my radar. Yes, inefficient, but likely a solution already on hand.

 

[Riley]

Have this tied to my 51.2v Lifepo4 Batteries, it keeps my 12v agm system at 12.3 if it gets low, Joe.
View attachment 75693

Wow, do you use your 48V battery as PV input? That's smart

 

[Joe BoyKey]

@Riley It's Dc to DC isolated buck converter, not intended for Solar, if 12v batteries drop to 12.2 then low voltage cut off board triggers relay and turns on Victron which holds batteries at 12.3 till the Sun comes out, rare but happens on multiple cloudy days. The 12v system is on the right in pic, critical loads on 12v system are listed, Joe.