openinverter forum

In my build I’ll be having 2 battery boxes, does the rear one need its own contactor, if so, when is it closed, I imagine before pre charge, so when the negative contactor closes, so does the rear battery box contactor, connecting the full pack together, then it starts pre charge etc

any HV battery needs at least 1 contractor and fuse to keep it isolated.

So yes.

run all the negative contractors off the same line.

In Germany's VDTÜV they just require one single-throw relay to interrupt the circuit. A car I owned a while back also had just that, 3 battery boxes, one relay. In Polo I had a front and a rear pack and just a double throw relay to interrupt the path from back to front.
I'd certainly recommend a fuse per box but adding a contactor to each should be up for debate. Hows everyone else doing that?

Bratitude wrote: ↑Thu Apr 01, 2021 4:09 pm any HV battery needs at least 1 contractor and fuse to keep it isolated.

So yes.

run all the negative contractors off the same line.

So my rear battery contactor (which won’t be on negative as it’s just one cable in and one cable out of the box) is run from the same line as my negative contactor

I like at least 1 contactor front and 1 contactor back. Fuse front, fuse back, I am also using an isolator front and an isolator back. (Came from HV world where there were lots of interlocks etc)

johnspark wrote: ↑Sat Jan 22, 2022 9:06 am I like at least 1 contactor front and 1 contactor back. Fuse front, fuse back, I am also using an isolator front and an isolator back. (Came from HV world where there were lots of interlocks etc)

Yes well, there were incidents where front box caught on fire. Then that fire melted the cables onto the chassis which caused a general meltdown which also melted the rear box with it.
Now if you would have contactors and fusees between boxes that would allow rear pack to survive and maybe not cause total loss. Worth to think about failure modes?

I'm adding a rear box at the moment, my plan is a pair of contactors and a fuse. Rear will be in parallel with front

Bigpie wrote: ↑Tue Mar 01, 2022 7:22 pm I'm adding a rear box at the moment, my plan is a pair of contactors and a fuse. Rear will be in parallel with front

That is different. Will you add a diode across contactor so you could use one charger for both packs?

Not following why I would need a diode?

If you want to have two battery packs in paralell you need to have them both connected for charging if you want to keep both packs same level. You could use a direct charger connection for first pack and a small contactor for 2nd pack, but control of that that is complicated. Much easier would be to have an IGBT transistor (its reverse diode) wired across contactor. Diode would conduct only in the case voltage on the first pack would be higher than on the second. That way you could charge the first pack and charge would "spill over" to the 2nd pack.

Still not following why its complicated? My plan was to have bms add the second pack after precharge and its confirmed cells are a close match in voltage