openinverter forum

Hello all,
Would be interested to know how Kokam cells are performing. Reading the posts, I understand that some of you have used this brand.
I am planning to build my own pack using 103 Ah Kokam cells, 66 of them in series. The size of the cell is width:268, length (tabs excluded): 265, thickness: 12.8 mm
Comparing this configuration to OEM battery packs, it seems simpler; but why do OEMs use smaller capacity cells, building modules by connecting the cells in parallel and series? Is it because of space restrictions, as the modules (as opposed to a long string of large cells) can be arranged to fit under the car’s chassis? I don’t have an answer and would be interested to know your opinion on using large size cells VS modules built with smaller cells.
Other considerations:
1. How to build the enclosure having in mind the criteria: cells need to be compressed, prevent water ingress and condensation, liquid cooling / heating (it’s Canada!), prevent the box from flexing, as this could cause the cells’ walls to rub one against each other.
2. BMS. Selection of a system. I would be interested to try Johhanes' BMS, but probably is not yet ready for sale. In regards to SimBMS, I couldn’t figure out if it is suitable for 66 cells connected in series. Of course the choice is related to the skill level of putting the system together. If it requires some soldering, wire connection and installation of software, then it is alright. Here, I would appreciate your guidance as well. There is so much information on the forum, but I still couldn’t decide.
Your opinions would be greatly appreciated.
Cheers,
Paul

PaulUdrea wrote: ↑Thu Sep 22, 2022 10:00 pm 2. BMS. Selection of a system. I would be interested to try Johhanes' BMS, but probably is not yet ready for sale. In regards to SimBMS, I couldn’t figure out if it is suitable for 66 cells connected in series. Of course the choice is related to the skill level of putting the system together. If it requires some soldering, wire connection and installation of software, then it is alright
Cheers,
Paul

Hi, do these have any BMS at all? If they have nothing, you could consider using Tesla BMS slaves combined with Teensy 3.2/SimpBMS. That would give you a stand alone fully configurable BMS. There is an option to use a little display with cell data as well. For 66S you'd need 11 Tesla slave boards. PM if interested.

Kokam are TOP cells. They even have a kind of safety built in that bricks the cell but car remains drivable.

I bult my box with cells lying on the side so contacts are accesible from front side. That way cells are compressed from top down. I advise not to build more than 8S packs. They are easier to handle.
For terminals I used copper sheets in sandwich and i bolted them to the terminals from both sides. Bolted not riveted! I used 5mm hex bolts with nuts and washers.
I used a lot of duct tape. It is light and effective.
Also do not forget cell sides all around conduct so they should be secured from touch... duct tape?

Heating? Maybe you can use electric lizzard heater pads? They are 230Vac as well as 110Vac. You can try them at 300Vdc, but you need to remove thermostat since it will be burned by DC. Or maybe just that 12V mobile home heating foil? It is 12V so i dont know if it is effective.

Or you can go full overboard and mount webasto fuel heater and one household thermostat to reroute some heated coolant to the battery heating manifold. There you basically make a floor heating inside your battery box. Be carefull though themperature should be no more than 40deg...

Or both systems if you want, i know it is cold in Canada in winter.

Thanks Arber and marty for your replies. Arber, I had a look at your blog and got the idea. Very helpful. Yes, a webasto is what is needed here in Canada. Before I go ahead I'll take more notes on information available here. Thanks for the feedback about Kokam.