Two BMS Boards In Series?

[Xsys]

Hello ES users!

I have an ebike, running 24s lipo at the moment. I want to get a BMS board to this battery pack, but its hard to find a BMS that works for 24s LIPO. Just wondering, is it possible to "split" the battery pack? In that way using two BMS boards, 12s each, in series to reach 24s. Or will the BMS board be toast because of the high voltage?

Currently looking at this one from BMSBattery: http://www.bmsbattery.com/smart/330-lifepo4lithium-ion-smart-bms-for-513-cells-in-series.html

I first looked at this one from Bestechpower, but their minimum order quantity is 2 units. I do not really need a second one... But if there isn't another alternative, I guess I'll have to buy two... http://www.bestechpower.com/888v24spcmbmspcbforli-ionli-polymerbatterypack/PCM-D131.html

Would be great if someone have an answer to this!

Cheers!
/Xsys

 

[parabellum]

Currently looking at this one from BMSBattery: http://www.bmsbattery.com/smart/330-lif ... eries.html

I would think twice before depositing my money and trust in this one.

And, it is possible running 2 BMSs in series, if manufacturer says its OK.

P.S. If its not OK, then add 2 diodes and its OK again. :wink:

 

[Xsys]

Ok, thanks Parabellum for clearing up that it's OK to connect two BMSs in series! But what do you mean by I should add 2 diodes if the manufacturer says it isn't OK to connect in series? And where should I add them? I'm not an expert on electronics

 

[Xsys]

BTW, How exactly do I connect the two boards together? I have a hum about how it's done, but I'm not exactly sure, wouldn't like to experiment and fail Would I add them up just like I would connect two batteries in series? Both with discharge and charge leads.

 

[parabellum]

Ok, thanks Parabellum for clearing up that it's OK to connect two BMSs in series! But what do you mean by I should add 2 diodes if the manufacturer says it isn't OK to connect in series? And where should I add them? I'm not an expert on electronics

You just connect diode in parallel to discharge leads of every BMS, kind of shorting them if polarity gets reversed, because it gets reversed on discharge leads of first pack to switch off. Diode will not conduct in normal condition but it should be capable to handle short spike of current your BMS is rated to deliver, you should also stop running after 1 battery switches off or program your controller to do so.

BTW, How exactly do I connect the two boards together? I have a hum about how it's done, but I'm not exactly sure, wouldn't like to experiment and fail Would I add them up just like I would connect two batteries in series? Both with discharge and charge leads.

If you permanently short charge and discharge leads on 1 BMS you risk it being unable to stop on LVC and HVC. At LVC it probably keeps discharging over charger leads and at HVC charging over discharging leads. But charging separately will work.
In other case you could find BMSs where charge and discharge leads are combined, but again, if 1 battery switches off on LVC, other could stay undercharged.

At the end 24s BMS is always better solution.