24v Single Bank 16s series/parallel or Dual Bank 8s in parallel?

[riverbug]

First time trying my hand at building my own lifepo4 battery banks. I want to go 24v (will be run with a 24v 3000 watt Victron Multiplus, and solar TBD) in an RV, and wondering if there is any disadvantage to option A below (preferred at the moment) versus option B?

Option A: Start with one 8s 280AH 24v bank, followed by a second 8s 280AH 24v bank, each bank to have its own BMS 24v 100amp, and configured in parallel. My thinking is this allows me to start with one bank and add a second later, as well as enabling me to easily run on one bank if I had an issue with either of them.
Option B: One 16s 280AH 24v bank with cells configured in series/parallel, with one BMS 24v 150 or 200amp.

I see people use option B but do not understand if this is done to reduce cost (one BMS vs two, less cabling, etc.), or if it is more efficient or better for longevity of the cells or other reasons?

 

[rodrick]

Option A is the best for the balance of cells 2 bms balancing is going to keep them in better shape and if you have to move them their lighter, my 8s 280Ah are quite heavy 16 is a no go for me and you will have to get a larger bms to get the amps needed on a 2p8s

 

[riverbug]

Option A is the best for the balance of cells 2 bms balancing is going to keep them in better shape and if you have to move them their lighter, my 8s 280Ah are quite heavy 16 is a no go for me and you will have to get a larger bms to get the amps needed on a 2p8s

Thank you for confirming. Very good point about the weight. Even if built in place, it would still be much handier to have two separate banks. I'm getting close to figuring this thing out I think. Will post my plans once I have them and see if I can get some feedback on whether I've made the right choices. Thanks again!

 

[MrM1]

yeah, I'd go 8s x2. You then must have 2 BMS. Yeah it adds a little cost, but it also adds to redundancy. with 2 independent parallel banks each with it's own BMS, you can take one off line for service if need be and not have to power down the system.

 

[Rednecktek]

Plus each battery pack only has to work half as hard to supply a given load. An 8s battery on a 100a BMS tops out at 2400w of load. 2 8s batteries on a 100a BMS each gives you 4800w of load max. Since you're wanting to go with a 3000w inverter, a single BMS will shut itself off before your inverter does.

 

[riverbug]

Plus each battery pack only has to work half as hard to supply a given load. An 8s battery on a 100a BMS tops out at 2400w of load. 2 8s batteries on a 100a BMS each gives you 4800w of load max. Since you're wanting to go with a 3000w inverter, a single BMS will shut itself off before your inverter does.

I was thinking I would install 2 200a BMSs so that if one bank was offline, it would still have headroom for the 3000 watt inverter. But the only 24v 200a BMS I can find so far is by Daly and the comments on the forum seems pretty mixed. Any ideas if there is a reliable BMS for 8s 24v above 150a?

 

[time2roll]

I would go with two batteries. Maybe three

 

[Rednecktek]

Docan has a JBD that'll do 200a @ 24v, but dual batteries is the way to go.

 

[riverbug]

Thanks all for the advice. And thanks @Rednecktek for the BMS info.

 

[Aussie Collie]

Don't forget fusing for each pack, between main pack positive and their combining busbar. Also a good idea to have a switch on each bank