Dual battery box, does rear need contactor

Post Reply
Domt177
Posts: 219
Joined: Sun Aug 30, 2020 6:05 pm
Location: West Midlands, UK
Been thanked: 11 times

Dual battery box, does rear need contactor

Post by Domt177 »

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
User avatar
Bratitude
Posts: 783
Joined: Thu Jan 02, 2020 7:35 pm
Location: Canada
Has thanked: 57 times
Been thanked: 168 times
Contact:

Re: Dual battery box, does rear need contactor

Post by Bratitude »

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.
https://bratindustries.net/ leaf motor couplers, adapter plates, custom drive train components
User avatar
johu
Site Admin
Posts: 5681
Joined: Thu Nov 08, 2018 10:52 pm
Location: Kassel/Germany
Has thanked: 153 times
Been thanked: 959 times
Contact:

Re: Dual battery box, does rear need contactor

Post by johu »

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?
Support R/D and forum on Patreon: https://patreon.com/openinverter - Subscribe on odysee: https://odysee.com/@openinverter:9
Domt177
Posts: 219
Joined: Sun Aug 30, 2020 6:05 pm
Location: West Midlands, UK
Been thanked: 11 times

Re: Dual battery box, does rear need contactor

Post by Domt177 »

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
johnspark
Posts: 264
Joined: Fri Apr 12, 2019 10:42 pm
Location: Adelaide, South Australia
Has thanked: 59 times
Been thanked: 48 times

Re: Dual battery box, does rear need contactor

Post by johnspark »

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)
arber333
Posts: 3241
Joined: Mon Dec 24, 2018 1:37 pm
Location: Slovenia
Has thanked: 74 times
Been thanked: 223 times
Contact:

Re: Dual battery box, does rear need contactor

Post by arber333 »

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?
User avatar
Bigpie
Posts: 1585
Joined: Wed Apr 10, 2019 8:11 pm
Location: South Yorkshire, UK
Has thanked: 74 times
Been thanked: 299 times

Re: Dual battery box, does rear need contactor

Post by Bigpie »

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
VW Beetle 2003
Outlander front generator
Prius Gen 3 inverter (EVBMW logic board)
Outlander charger
3x Golf GTE batteries
Chademo Charging
Outlander water heater
arber333
Posts: 3241
Joined: Mon Dec 24, 2018 1:37 pm
Location: Slovenia
Has thanked: 74 times
Been thanked: 223 times
Contact:

Re: Dual battery box, does rear need contactor

Post by arber333 »

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?
User avatar
Bigpie
Posts: 1585
Joined: Wed Apr 10, 2019 8:11 pm
Location: South Yorkshire, UK
Has thanked: 74 times
Been thanked: 299 times

Re: Dual battery box, does rear need contactor

Post by Bigpie »

Not following why I would need a diode?
VW Beetle 2003
Outlander front generator
Prius Gen 3 inverter (EVBMW logic board)
Outlander charger
3x Golf GTE batteries
Chademo Charging
Outlander water heater
arber333
Posts: 3241
Joined: Mon Dec 24, 2018 1:37 pm
Location: Slovenia
Has thanked: 74 times
Been thanked: 223 times
Contact:

Re: Dual battery box, does rear need contactor

Post by arber333 »

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.
User avatar
Bigpie
Posts: 1585
Joined: Wed Apr 10, 2019 8:11 pm
Location: South Yorkshire, UK
Has thanked: 74 times
Been thanked: 299 times

Re: Dual battery box, does rear need contactor

Post by Bigpie »

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
VW Beetle 2003
Outlander front generator
Prius Gen 3 inverter (EVBMW logic board)
Outlander charger
3x Golf GTE batteries
Chademo Charging
Outlander water heater
Post Reply