2 8s bms in series

[Jimmynik1]

In one of Wills most recent videos he made a 48v 320ah bank. I bought 16 310 cells with 2 daly 150a 8s bms and I initially intended on making a 620ah 24v system but was persuaded to 48v for its seemingly endless benefits. So my intention now is to series my 2 already bought 8s bms.
In his video towards the beginning he says "i cant get a 16s bms, so I'm going put 2 8s in series"
Then further along in the video it just happens with no clear instruction or anything. From the finished product shot in the video around the 9:20 mark it looks like 2 separate 8s packs which he described and then one bms on either end.
Asking the group now how this is done or is it just as simple as it sounds?
Appreciate the help.

 

[RCinFLA]

Not advised unless you are sure the series pass MOSFET's have high enough voltage rating.

Most 8S BMS have 40v rated MOSFET's. 16S BMS have 80-100v rated MOSFET's.

Also why you need to be careful of series stacking 12v self contained LFP batteries. Battleborn batteries, for example, spec their 12v batteries are capable of stacking up to four in series for 48v system. They use 100v breakdown MOSFET's in their battery's internal BMS's.

Some of the cheap 12v LFP's use 20-25v rated MOSFET's in their BMS.

 

[Jimmynik1]

Not advised unless you are sure the series pass MOSFET's have high enough voltage rating.

Most 8S BMS have 40v rated MOSFET's. 16S BMS have 80-100v rated MOSFET's.

Also why you need to be careful of series stacking 12v self contained LFP batteries. Battleborn batteries, for example, spec their 12v batteries are capable of stacking up to four in series for 48v system. They use 100v breakdown MOSFET's in their battery's internal BMS's.

Some of the cheap 12v LFP's use 20-25v rated MOSFET's in their BMS.

Thanks, better to just go with the correct 16s bms?

 

[Scph9002]

Doesnt he connect 2 24v batteries with their own 8s bms into series? How can that become 48volt through just one singe bms thus damaging its mosfets?

Maybe if you connect bms1 p- to bms2 b- floating not grounded to 24volt cell stuff gets dodgy

 

[Jimmynik1]

Doesnt he connect 2 24v batteries with their own 8s bms into series? How can that become 48volt through just one singe bms thus damaging its mosfets?

Maybe if you connect bms1 p- to bms2 b- floating not grounded to 24volt cell stuff gets dodgy

No idea

 

[RCinFLA]

 

[Scph9002]

View attachment 63739

Great, thanks !

 

[Amitis]

In one of Wills most recent videos he made a 48v 320ah bank. I bought 16 310 cells with 2 daly 150a 8s bms and I initially intended on making a 620ah 24v system but was persuaded to 48v for its seemingly endless benefits. So my intention now is to series my 2 already bought 8s bms.
In his video towards the beginning he says "i cant get a 16s bms, so I'm going put 2 8s in series"
Then further along in the video it just happens with no clear instruction or anything. From the finished product shot in the video around the 9:20 mark it looks like 2 separate 8s packs which he described and then one bms on either end.
Asking the group now how this is done or is it just as simple as it sounds?
Appreciate the help.

Actually Daly 8s 100A BMS use high quality 100V, 150A@25°c , N channel mosfet with Rds(on)=4mohm, so in the theory you shouldnt have problem to series them But it doesn't yet recommend in its datasheet to series them but according mos spec and as William tested it I dont think there was a problem. Instead you can use JBD smart bms series 4s 150Ah with 80v MOS it is allowed to series up to 4x 12v battery pack.

 

[Just John]

Some JBD BMS are rated for 80v, some are not. Read the spec sheet, they will tell you. Better yet, just buy a 48v BMS.

 

[time2roll]

At this level I am not sure what the endless benefits of 48 vs 24 volts actually is..... unless you have bought 48v equipment already, I would shift back to 24 volts.