24v as 2 packs of 4

[BigGElmo]

Hi, I've built a nice 24v 304ah EVE LiFePO4 battery with a JK BMS to power my Camper van, the 8 cells are in a plywood box and are under compression.
My problem is that the battery box is on the floor in the main living area and I'd really like to lose it to gain more floor space, my only option is to split the pack in to 2 seperate 4 cell packs and place one pack of 4 cells in each of the driver and passenger seat bases, but with the packs in the seat bases the BMS balance wires will now be to short.
So what are my options ?
A 4s BMS for each pack ?
Lengthen the BMS balance wires ?
Or what else can you suggest.
Cheers from the UK.

 

[time2roll]

I would lengthen the balance wires and keep it as a single battery single BMS. I assume the distance is not excessive.

 

[TorC]

I agree with @time2roll. I have a thread here which looks at the practicalities of the balance wire lengthening: https://diysolarforum.com/threads/solved-extend-lengthen-bms-sense-balance-wires.55010/

 

[BigGElmo]

Thanks for the helpful replies.
TorC I read through you post and rhino mentioned using terminal blocks to join the balance leads together which I have seen done by a YouTube vlogger from "Sunny hot Australia" that I follow.
This morning I had a brainwave while in the shower about how to mount the packs of 4 cells in the seat base frames add this to your comments and I now have a plan so I'll start gathering all the parts needed.

Just one last question.....
Will the temperature sensor wireing also extend OK in the same way ?

 

[TorC]

It should. There's no reason to expect you have enough EMF in the area to confuse it under about ten feet. That said, you can also consider whether you really need the temp sense in that side of the battery, or you are comfortable on the assumption that both are basically in the same space, and therefore should be more or less the same temperature.

 

[SolaroSsaurius]

It's not just the BMS sense wires that have to be extended, also two thick cables have to go through the seat bases, in a place where there is a lot of walking, which may require some thinking

 

[BigGElmo]

Hi again and thanks for the reply.
I've sorted the install of 2 packs of 4 Eve B 304ah cells in the seat bases of my Renault camper van build.
I had a local metal fabricator cut and fold some 2mm Zintec coated steel to form the battery supports, these supports are clamped between the top of the seat base and the underside of the seat swivel bases, they are located with self tapping screws.
The Eve cells have 1mm self adhesive foam stuck to the sides and ends to reduce cell to cell contact and to increase the pack grip on the inside of the support frames the cells are also under a small amount of side compression.
I have glued 18mm ply wood to the side of the support frames to mount the main fuse holder and the JK BMS to.
The 35mm2 main live cable and 35mm2 link cable between cell 4 & 5 are run in flexible trunking under cab floor mat.
I have lengthened all the BMS balance wires to approximately 1200mm and connected them to the shortened standard balance loom with terminal blocks mounted on a DIN rail, I have increased the new balance wire size to 18awg from the original 20awg to reduce the longer balance wire resistance, all the wire ends are fitted with crimp terminals.
The P- main negative passes through the seat base with a bulkhead fitting.
I've left the temperature sensor wiring as standard and it inly measures the temps of the cells 1 to 4 which are in the seat base nearest the BMS, if anyone knows of an extended temp sensor loom for a JK BMS then please let me know, I have checked the temps of all the cells with a digital lazer thermometer and cells 5 to 8 are slightly warmer by 0.5°c as the seat base they are in is closer to the diesel parking heater outlet which is currently ticking away on minimum setting waiting for the predicted "Beast from the East" cold snap and snow fall to appear in the next few days.
I had to make an emergency stop yesterday while out in the van and neither of the 4 cell packs moved in the support frames.
My next job is to make a pair of plastic covers to cover the cell terminals which are currently open to small objects falling onto them........not good.

 

[hwse]

One of the very nice features of the JK is that it samples the resistance of the sense wires and adjusts itself accordingly. Nami had said last year that they can be extended up to 32" long and I assume that would be based on using the same gauge wire. If I needed to go a bit beyond that, I would use a wire a size bigger. The JK sense wires are always a larger gauge than the passive balance BMS's because they carry the full 2A of current.
Another nice thing about the JK is that all of the sense wires do not need to be the same length. I trimmed each of mine to be the correct length for my string 8-cells long and when I fired it up the first time, you could see that the IR of each wire increased with the length of the wire.