Fitting 200ah of LFP into an 'L' shaped moulded boat battery box

[David Pocock]

I've got a 32 foot Sadler sailboat that has a moulded battery box which fits two standard sized 100 ah sealed lead acid batteries. I'd like to use the same space for 200 ah of LFP, ideally making a single battery rather than two batteries in parallel. A 200ah 4S batttery is too big so I have been wondering about a 2P4S battery but with the two halves at right angles to each other. The series connection between the two 2P2S halves might have to be a bit longer than the other series connectors. Will that introduce cell imbalance over time?

 

[John Frum]

Will a drop in replacement such as a battleborn not fit?
What is the form factor of the current lead acid batteries?

 

[Barold]

I have a similar desire, but my understanding is that at the junction, your wire connectors would have a different resistance than the busbars and therefore your power draw will not be consistent across all the cells. I've thought about the alternative of 2 1P4S batteries wired in parrallel but I believe there are concerns with that as well as needing two separate BMS

 

[SCClockDr]

I've got a 32 foot Sadler sailboat that has a moulded battery box which fits two standard sized 100 ah sealed lead acid batteries. I'd like to use the same space for 200 ah of LFP, ideally making a single battery rather than two batteries in parallel. A 200ah 4S batttery is too big so I have been wondering about a 2P4S battery but with the two halves at right angles to each other. The series connection between the two 2P2S halves might have to be a bit longer than the other series connectors. Will that introduce cell imbalance over time?

A diagram, hand or cad, would assist me in seeing what you intend.

 

[David Pocock]

Will a drop in replacement such as a battleborn not fit?
What is the form factor of the current lead acid batteries?

Thanks for the quick reply. Group 31 size. It would take some drop-ins but I want to be able to separate the charge and load buses.

 

[David Pocock]

I have a similar desire, but my understanding is that at the junction, your wire connectors would have a different resistance than the busbars and therefore your power draw will not be consistent across all the cells. I've thought about the alternative of 2 1P4S batteries wired in parrallel but I believe there are concerns with that as well as needing two separate BMS

Thanks. It looks like the only way to do it would be for the series connector between the two 'halves' would be the same as all other series connectors.

 

[David Pocock]

A diagram, hand or cad, would assist me in seeing what you intend.

Not quite CAD ...

 

[SCClockDr]

Looks good to me. Make a mock up of foam blocks that match the shell specs to confirm fit.

 

[David Pocock]

Looks good to me. Make a mock up of foam blocks that match the shell specs to confirm fit.

Good idea. Actually, now I've drawn it out, it looks possible as long as the terminals are equidistant to side and nearest end of the cell so the connectors can be the same length.

 

[SCClockDr]

In a series string 1 differing link will be easily tolerated. Differing parallel inter-conecting cable lengths are what to avoid.

 

[David Pocock]

In a series string 1 differing link will be easily tolerated. Differing parallel inter-conecting cable lengths are what to avoid.

That's even better news. Thanks!

 

[MisterSandals]

That drawing is wrong.
The connection between the bottom 2 cell pairs needs to be on the very bottom.

 

[David Pocock]

That drawing is wrong.
The connection between the bottom 2 cell pairs needs to be on the very bottom.

Thank you. Well spotted!

 

[bostonbuzz]

Aluminum cased cells are only ~5” x 5” for 110ah 12v, so 200ah might fit. 11.8” total. They are 37.5mm thick each. I ordered 8 at 411$ shipped = the best deal around. Other posts talk about these cells. Here

 

[David Pocock]

Aluminum cased cells are only ~5” x 5” for 110ah 12v, so 200ah might fit. 11.8” total. They are 37.5mm thick each. I ordered 8 at 411$ shipped = the best deal around. Other posts talk about these cells. Here

Hmm .. that is small. Thanks for the heads-up.