FLA LA (FLA,AGM,GEL) 100%SoC House System

[rgleason]

Ok. Understood. This idea was to use a cheap 80ah starting battery or maybe an agm with acceptance rate of .4C to fully charge the house bank of FLA, using a sterling b2b rather than long hours of engine alternator operation. This might be accomplished with several rechargings of the starting battery by engine/alternator.
This would simply be a second use for the start/reserve battery, which would be recharged with some small solar pv up to full.

A sterling b2b would be needed, but no LFP BMS would be needed.

[john61ct]

But do you still think it could be a good idea?

The point of an LFP bank as source is that it does not get destroyed in the process.

But if the low efficiency argument holds then even that is only going to be workable if the big Main bank is LFP (source) and the target lead one is smaller Reserve.

And even if it works, does not mean worth implementing

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Many if not most LFP DIYers have no BMS as usually defined.

Just need to be careful, you can be the BMS yourself.

Of course some more risk averse, or perhaps with more money or both, will howl with outrage at the suggestion.

[rgleason]

John wrote:

Many if not most LFP DIYers have no BMS as usually defined.

Just need to be careful, you can be the BMS yourself.

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How often do cells need balencing with careful wiring? How often should this be checked?
I assume that as a bare minimum I should have a Victron device that alarms, then cuts off low voltage and high voltage.

I guess you'd favor LFP for house bank and a smaller LA reserve bank that is charged from the house ( with or without a sterling b2b?) and is used just as backup. All charging (alternator, solar and shore charger) would be done directly to the LFP?

I suppose the BMS could be added later.

What kind of battery box is needed? Can they be put on their side? If so might be able to fit them on top of the keel watertank under the cabin sole.

LFP definitely appear to be the most reasonable answer to PSoC abuse and long and wasteful engine alternator run times.

Save $1300 on solar, upgrade alt to balmar or mg 120a or 140a serpantine for $1200 to $1400 and do the rewire for an LFP house bank of perhaps 200-300ah with room for expansion, in the cabin on port side or on top of the keel water tank. Small 100watt solar on dodger and future bimini can be done later.

Just rewiring is going to be expensive.

Sell the 1 year trojan T-105 which are to tall to fit under the port seat.