DIY storage battery from BEV cells

[Marcus]

“Highly dangerous”?

I think you should put down the pearls and apply a bit more common sense! In the real world it all, comes down to how hard you’re running the batteries. 2C? You definitely should consider temperature measurement (and active heating/cooling). 0.2C? Just not required!

Yes highly dangerous.

I know common sense is highly frowned upon now but I have loads of it and use it all the time.

It's nothing to do with how hard you are running them.

You're welcome to carry on thinking that. However it isn't true. Clutching pearls and spreading baseless fear isn't allowed on this forum. I'm not the policeman around here. But I should warn you that others have been booted for similar...

I wouldn't go as far as 'highly dangerous' but, spending ££££ or even £££££ on battery cells, and then placing your trust in a single electronic voltage control system to ensure they never get over/under charged or charged when too cold, seems a bit silly if you can add an independent backup system (bms) for ££.

I've seen a few too many failed electronic devices (including mppt charge controllers failed short cct - so they just pass all charge to the battery) to rely on one system without an additional failsafe. Even when my battery was all lead acid (which are quite abuse resistant) i would usually have one backup system.

I suppose if your batteries are in an outbuilding and you have the £££££ to replace everything if it all goes pear-shaped you could take the minimalist approach.

[ALAN/ALAN D]

Mr Tinbum wrote.

I'd never ever run batteries without a bms


When you factor in the Design of the BMS. ??????????

The cable diameter of each cell balancing connection is big enough
to pass a few milliamps for charging and for monitoring the cell voltage.


All the individual cell cables leaving the BMS are twisted together with a protective external cover. One cell balancer out put device fails short circuit. A very large current flows through the single cable that is wrapped amongst the rest of the balance circuit. The whole 16 cells join together / system catches FIRE.

There is not a fuse fitted onto each cell balance cable.

I have bought two different systems. Either one has not been installed because you only have to look at what came out of the box to work out that they are not fit for purpose and create a severe fire risk.

[Tinbum]

Mr Tinbum wrote.

I'd never ever run batteries without a bms


When you factor in the Design of the BMS. ??????????

The cable diameter of each cell balancing connection is big enough
to pass a few milliamps for charging and for monitoring the cell voltage.


All the individual cell cables leaving the BMS are twisted together with a protective external cover. One cell balancer out put device fails short circuit. A very large current flows through the single cable that is wrapped amongst the rest of the balance circuit. The whole 16 cells join together / system catches FIRE.

There is not a fuse fitted onto each cell balance cable.

I have bought two different systems. Either one has not been installed because you only have to look at what came out of the box to work out that they are not fit for purpose and create a severe fire risk.

I've thought that myself but it's also the same with active balancers- they very rarely seem to show fuses and they normally have heavier duty cable than a passive balancer that's on most BMS's.

I'm guessing here, that the fault current is so large that the cable itself acts as the fuse or the pcb track fails on the bms. I've never seen all 16 cables in one bundle though and some kits use pcb's to the cells which would also act as a fuse. Nothing to stop you putting fuses in on a DIY pack which is what I would do.

[diyfan]

hi all,

There has been some developments in the last couple of weeks. I received the inverter and commisioned it. Also received the Kia BEV battery modules. The set contains 10 modules - 8 x 10S3P (30 cells) and 2 x 9S3P (27 cells). The total amount is 294 cells.

Tearing down the modules is very easy, everything comes apart without breaking and could easily be re-assembled. It would not be too dificult to repair such module in case cell replacement is needed. Everything is fastened with M8 screws and a couple of plastic clips. As already mentioned the cells are arranged in 10 or 9 triplets. Cell tabs inside triplet are welded in parralel on to a busbar essentially forming a 180ah combined cell. These are then all connected in series to form the 180Ah module.

The cells are SK INNOVATION E600B and below are the specs based on the spec sheet I found online:
Nominal voltage: 3.65V
Nominal capacity 63.2 Ah
Watt-hour rating: 230.68 Wh
Max final charging voltage: 4.2V
Min final discharging voltage: 2.5V

So I have assembled one 14S3P battery prototype, hooked up a BMS I used for another project and connected to the inverter via switch/ resettable fuse and started to do some limited proof of concept testing. The thermal image is after 30 minutes under 60 amp load. Everything looks very promising, no major challenges. But will still need to build fire proof outdoor casing, source proper BMS, correctly rated cables, fuses, isolator and other minor things to make it look nice, tidy, out of the way and as safe as possible.

That's it for now. Hope someone will find this interesting or useful. Stay safe and a Happy New Year!

[Joeboy]

Nice one diyfan!

Did anyone ask you the price paid for the EV pack? Big modules in comparison to the multimeter. Are they fluked for cooling, looks like they are.

Congratulations again!