Franken-battery experiment

[Swamplizard]

Hello All - I successfully built a nice 280AH 24V for my Overlander and will be adding another 400AH shortly and will do it 100% "right".

However, I have accumulated a few LifePO4 batteries of various sizes and manufacturors and need a small battery to drive some stuff on my boat - low Amps, low expectations, 12Volt, nothing critical or crazy....so thought I would cobble together a franken-battery and break some rules and see what I get out of it.

Will use EPEVER MPPT to charge with a couple flexible solar panels and will of course have an appropriate BMS. Will not be pushing these by charging all the way to 3.65v ... conservative setup.

Inventory:

2 75AH new
2 72AH older
4 50AH older
4 180AH new

Chemically they are all similar LifePO4s. All can be charged to 3.6 without any perceptable swelling.

Thinking 4x180s one one BMS, 2x75s and 2x72s on another BMS, and 4x50s on it's own BMS. Connect all three "packs to a bus bar with fuses and the MPPT. Theretically would end up with 302AH of 12volt capacity which would be a decent house battery for the boat.

Pros/cons?

Thanks for inputs.

 

[OffGridInTheCity]

Paralleling the 4 will work and since it's not 'crazy' different capacities and sounds like light loading and low stress DOD - it may work very well for your use case. Seems like the main 'con' would be a little extra stress leading to a bit shorter life on some of the cells - but with low stress loading/DOD will it really be that much? Will be interested to see other comments and any follow up posts

 

[Swamplizard]

Need to find some relatively cheap BMSs - in Florida so wont need low temp shut off 50-60 amp should do it. Seems like the Daly's try to over-charge cut off at 3.75 - would prefer to have it at 3.65 but I guess I can set the charger/MPPT to lower

 

[BradCagle]

Yup, I think your plan will work out just fine.

BTW you'll probably want to set the charge voltage lower anyway, say 3.45v per cell, as you're bound to have a cell or two that likes to peak up faster than the rest.

 

[DThames]

JBD BMS with Bluetooth gives you a good phone base monitor. Also, i have one of these battery monitors and you can set a low voltage alarm so you can hear it beeping before your BMS does a hard shutdown.

 

[DThames]

Yup, I think your plan will work out just fine.

BTW you'll probably want to set the charge voltage lower anyway, say 3.45v per cell, as you're bound to have a cell or two that likes to peak up faster than the rest.

I have an old battery and for 24v, 27.1v or 27.2v works well to stop those "runners".

 

[Swamplizard]

Thanks Guys!