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Old 18-01-2025, 22:45   #1
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Engine, house, solar batteries

Sorry, I know this has been beaten to death, but here goes, actually on a motorhome, but I don't think the electricity cares.

1) Engine battery charges from alternator
2) House SLA battery charges from alternator and shore via direct charger.
3) Solar 300AH LiFePo charges from solar which supplies an inverter with manual switch.
4) 220 from inverter is a separate circuit from the 220 shore connection circuit now.

I'd like to make the solar primary, have a single 220 circuit, and charge the house battery automatically from solar, also.

Can a DC/DC charger from the sometimes 14+ voltage of the LiFePo just keep the house SLA at 13.? without overcharging or discharging the LiFePo below some threshold?

Can a Transfer switch be configured to supply a single 220 circuit when shore power is available and automatically turn on the inverter and connect it to the combined 220 circuit when shore not available?

Is it advisable to have another DC/DC from LiFePo to the engine, especially during extended storage.

BTW, I'm in New Zealand, now, but have similar needs for a US system.
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Old 19-01-2025, 04:47   #2
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Re: Engine, house, solar batteries

I’d imagine:

Alternator to starter.
DC Cable from starter goes to Automatic Charge Relay (ACR). This only allows current to pass if either side is over say 13.2V for x minutes. An ACR would, if house banks are in great shape also charge your starter.
The ACR cable goes to a common DC bus.
Yacht 12V loads run off DC bus via your DC elec distribution board.
If your lifepo4 have own BMS then it also simply connects off the DC Bus.
You seem to have another lead acid bank, probably it sits with a DCDC controller also onto that DC Bus.

The battery inverter likely can:
1. Take shore AC power.
2. Take generator AC power (unless you have a rectifier in which case the gennie supplies DC to that DC bus).
(note that 1 and 2 would be an either or via a switch on AC panel so as cannot run gennie and shore power concurrently)
3. Take DC from that DC bus to supply your AC electrical distribution board.
4. Take DC input from solar for mix of live use as AC and charge input to the DC bus.

If your lifepo4 battery is 52V then need a 52:12 DCDC controller between it and the DC Bus so that can keep your 12V loads on the old DC bus and then the battery inverter is likely also 52V and it would be directly connected to the 52V lifepo4.

Obv fuse protected everywhere, and I would have Ah meters via shunts at the Neg pole of the lifepo4 and acid house bank.
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Old 19-01-2025, 09:01   #3
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Re: Engine, house, solar batteries

An Orion DCDC charger can be configured as you need to charge the house SLA batteries from LFP.

Will Prowse describes a smaller transfer switch. I have no idea if there are issues with this on a boat or RV.


Use the same DCDC to maintain your SLA and your house from the LFP with an ACR.
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