Re: off-grid - battery & winter 12V-generator?

"Richard Smith"  wrote in message news:[email protected]...

I am reading and thanks, yes this is a journey into the topic.
BTW with "car alternator" I was thinking get one from a scrapped car and
spin the alternator with the small gasoline engine.  Even the smallest
"GX" engine at 100cc is looking a little overpowered for this.  On the
plus - I hear many car alternators have a built-in regulator ?
Rich S

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I've considered this too and have an alternator, besides incompatible belt 
types the stumbling block is that car voltage regulators aren't adjustable 
and I like to follow maker's numbers for the lead acid bulk, absorption and 
float stages, plus DC desulfation if needed. For LiFePO4 I use the AGM or 
similar float voltage and occasionally raise it to take the battery to its 
cutoff and balancing voltage. Also I update my current-measuring charge 
level monitor to 100%.
https://www.batteryuniversity.com/article/bu-403-charging-lead-acid/

However if the grid and your battery bank are down those are minor 
considerations, you take what you can get. A larger concern may be that the 
charging battery needs to be close to the outdoor generator, not your indoor 
inverter and load. Power travels with much less loss or wire expense at 120V 
than 12V. I have the welding transformer charger which gives nearly the same 
result with better control and monitoring at the inverter battery, powered 
by 120VAC from a generator.

Drok offers a voltage adjustable and current limited supply that's nearly 
what I want but the voltage apparently doesn't go quite high enough, I'd 
like 16V to allow an anti-backflow diode.
https://www.ebay.com/itm/800378599533?

While we are at it...
It's claimed that LiFePO4 deteriorates internally when near or at full 
voltage, the storage recommendation is ~60% SOC. However the same people say 
to charge to 14.4V which trips cutoff.

<a battery maker> told me that 13.6V is a good charger voltage, just below 
cutoff. The battery still charges rapidly to around 90%, then the current 
tapers down, but you wouldn't know this unless you display the current as 
well as the voltage.

Charging LiFePO4 to 13.6V like AGM and even paralleling them is 
controversial, it has advantages and cautions. For me the advantage is that 
when the LiFePO4 reaches full charge and suddenly disconnects the AGM 
absorbs and prevents a voltage spike to full panel open circuit voltage 
before the solar controller can react. This protects the connected inverter 
from overvoltage which broke one of mine.

The caution is that an AGM at higher than ~12.8V rest voltage draws leakage 
current from the LiFePO4. The two C&D 77Ah AGMs I have in parallel draw less 
than 1/2 Amp but some can take more as they age. I shut off their breaker in 
the evening if I think of it but the loss isn't that significant. During 
overcast it stays off because the LiFePO4s won't fully charge.

The LiFePO4 provides all the current down to around 12.6V where it's nearly 
depleted, then the AGM smoothly takes over. The full discharge endpoints of 
both are similar and setting load cutoff a little higher like 11 - 11.5V 
gives up little capacity without completely draining either.

I hope that's enough but not too much.