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diy solar

Switching to LifePo4 advice needed

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Byrogie

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Oct 22, 2020
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Preliminary research into switching to LifePo4 batteries from FLA for my RV, which is parked in seasonal campground lot.
Currently have 675 Ahr, 6x6 volt GC-2 batteries, 2x280 watt solar panels, 24 volt nominal wired in series, 40 amp/100 volt programmable MPPT charge controller,
2000 watt inverter/charger (100 amp adjustable/programmable) hardwired to RV. Portable 3000 watt generator.
Of course I am budget conscious, don't have the coins to buy Battleborn, etc.
So far I like the 280 Ahr cells floating around, either get 4 or 8 with a good BMS.
Can I use my existing equipment?
Recommendation for a quality BMS? Or any other advice is welcome.
 
8 280Ah cells w/ 2X BMS (basically 2X 12V batteries) will run you $1300-1400 if you DIY. That's equivalent to 5+ BBs and about 85% as much capacity as your existing system if looking at the total and about 80% more if you look at the 50% usable of the FLA.

Provided your MPPT charge controller is fully programmable for boost/bulk/absorption and float voltages, it shouldn't be a problem. You will need to disable equalization or set it to the float voltage.

If the battery is also charged via a 120VAC to 12VDC converter when on grid/genny, you need to ensure the converter output voltages make sense. If not, you can replace it for less than $200 with one that works well with LFP. If charge voltage does not exceed 14.6V and float does not exceed 13.6V, then it's fine. If it's one of those 13.8V constant voltage units, it's not a good choice unless it's used very infrequently.
 
snoobler said:
8 280Ah cells w/ 2X BMS (basically 2X 12V batteries) will run you $1300-1400 if you DIY. That's equivalent to 5+ BBs and about 85% as much capacity as your existing system if looking at the total and about 80% more if you look at the 50% usable of the FLA.

Provided your MPPT charge controller is fully programmable for boost/bulk/absorption and float voltages, it shouldn't be a problem. You will need to disable equalization or set it to the float voltage.

If the battery is also charged via a 120VAC to 12VDC converter when on grid/genny, you need to ensure the converter output voltages make sense. If not, you can replace it for less than $200 with one that works well with LFP. If charge voltage does not exceed 14.6V and float does not exceed 13.6V, then it's fine. If it's one of those 13.8V constant voltage units, it's not a good choice unless it's used very infrequently.
Click to expand...
Thanks, snoobler. No converter in use. Inverter/charger is wired to trailer electrical and is programmable. Equalization can be disabled.
If I use 8, is it possible to connect them to use 1 BMS?
 
Yes, you can 2P4S (2 cells in parallel, 4 groups of paralleled cells wired in series) the battery, but you lose all redundancy, and have no functional battery if even one cell goes out.

DIY means doing the work and actually testing the batteries, so you'll need another $100 or so in power supplies and capacity testers and days of time to do it.
 
Speaking from my own negative black smoke military helicopter fly by experience, don't listen to anyone who might say to not worry about a BMS. Also make sure to put in a fireproof air sealed box (think ammo can). Don't use automotive grade chinese circuit breakers (the square flat kind). Install temperature alarms and smoke detectors if indoors (not recommended). Try to keep parallel cells to a minimum to allow the BMS the most accuracy.



RIP 20x surplus electric bus LiFe battery packs... you will be missed.
 
dehv said:
Speaking from my own negative black smoke military helicopter fly by experience, don't listen to anyone who might say to not worry about a BMS. Also make sure to put in a fireproof air sealed box (think ammo can). Don't use automotive grade chinese circuit breakers (the square flat kind). Install temperature alarms and smoke detectors if indoors (not recommended). Try to keep parallel cells to a minimum to allow the BMS the most accuracy.

RIP 20x surplus electric bus LiFe battery packs... you will be missed.
Click to expand...

Why?
 
because reasons? One cell can cause cascading failure, and a lack of oxygen will extinguish a fire quicker and protect the building it may be enclosed in.

OP requested advice, my opinion is this.
 
dehv said:
because reasons? One cell can cause cascading failure, and a lack of oxygen will extinguish a fire quicker and protect the building it may be enclosed in.

OP requested advice, my opinion is this.
Click to expand...
Ok, you are talking about lithium cells. I think [and hope] that this person wants to install Lifepo cells which have been shot with a gun, short circuited, set on fire, put in ovens and much more and yet never catch fire.
Have a look into them. They are extremely safe which is why I recommend them to the seniors and disabled where I live for their scooters when they need to replace the AGM's they have.
They are pretty cool. :)
 
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