Mppt inverter as dcdc charger

[GoneDiving]

Originally Posted by CapnBazza

Thank you for this question. Using my redundant Blue Sky Solarboost 2000e as a dc-dc charger to keep my standalone start battery topped up from my LiFePO4 house bank to avoid a flat start battery after prolonged non use, had not occurred to me. I thank you for the suggestion. Thinking about it, I can’t see why it wouldn’t work. The Solarboost just sits there doing nothing, using it like this means it earns the space it occupies.

You're welcome. My intended use is to keep a dedicated start battery charged on an engine that currently has no altenator fitted

[fxykty]

Just to emphasise a point, you can use a solar controller to charge a lower voltage bank (12V in the OP’s example) from a higher voltage bank (48V). This won’t work if the banks have the same voltage or the source bank is a lower voltage.

In those cases you would need a DC-DC charger.

[Emmalina]

Originally Posted by GILow

Really? How?

If your charge controller can,t or doesn't limit the input current it will draw enough current to damage its output stage.

[CapnBazza]

Originally Posted by fxykty

Just to emphasise a point, you can use a solar controller to charge a lower voltage bank (12V in the OP’s example) from a higher voltage bank (48V). This won’t work if the banks have the same voltage or the source bank is a lower voltage.

In those cases you would need a DC-DC charger.

I intend to set the Solarboost to charge a FLA 12v battery. The lithium house batteries are charged via a Victron 100/50 Smart Solar controller or, when alongside, a ProNautic 12.40P battery charger floating at 13.8 volts. Does that sound OK?

[markcouz]

I don't think it will work.

While I am not familiar with the Solarboost, if it is an MPPT as is being discussed here then the house bank voltage is not high enough to charge a 2nd 12v bank (typically around 18v and above would be required).

In your case you would require a DC-DC charger.

Originally Posted by CapnBazza

I intend to set the Solarboost to charge a FLA 12v battery. The lithium house batteries are charged via a Victron 100/50 Smart Solar controller or, when alongside, a ProNautic 12.40P battery charger floating at 13.8 volts. Does that sound OK?

[mitiempo]

Originally Posted by markcouz

I don't think it will work.

While I am not familiar with the Solarboost, if it is an MPPT as is being discussed here then the house bank voltage is not high enough to charge a 2nd 12v bank (typically around 18v and above would be required).

In your case you would require a DC-DC charger.

I agree.

The op has a 48 volt bank so it works for him.

[GILow]

Originally Posted by Emmalina

If your charge controller can,t or doesn't limit the input current it will draw enough current to damage its output stage.

Never heard of a solar controller that does that. All that I have met are limited by output capacity and input voltage. Are there some we should be wary of?

[GILow]

Originally Posted by markcouz

I don't think it will work.

While I am not familiar with the Solarboost, if it is an MPPT as is being discussed here then the house bank voltage is not high enough to charge a 2nd 12v bank (typically around 18v and above would be required).

In your case you would require a DC-DC charger.

Agreed. And Dc to Dc chargers are not horribly expensive.

[Cowpoos]

Originally Posted by GoneDiving

I'm looking for a step down dcdc charger to run off my 48v Lifepo4 house bank to charge a infrequently used 12v SLA battery.

Can I use a 20a 12v mppt solar charge controller with my 48v house bank replacing the PV input? Is the input/output of the controller governed to its rated capacity or will the house bank supply essentially unlimited current and fry it?

Thanks.

I will work fine with a Victron mppt. I have been using my spare 100/30 as a shore power connected to a 480w LED power supply.