BMS Common vs Separate port

powerX

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Feb 25, 2020
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Hello,


Could someone tell from ownexperience which of the BMS is better? With common or separate ports?


Some people say that common is much better, but ifound information where separate is also have advantages.


got confused :|

t.y.


image_sfuaug.jpg
 
Common port is for systems where you have the load and charger coming from same source.

Split source /load is generally made for where you want the BMS only to cut the charger and not the load. Like Ebikes.
 
But on the powerwall its more important do not cut the load. while ebike is charging not while the driving so whats the problem to cut the load (motor) if the bike is charging plugged in to the socket?
 
How do you intend to start using an ebike IF load output is cut after charging? Once again IF you have separate Charge and load use separated ports. Unless your Charger talks to the bms
 
OK. looks like i still have a gap of knowledge about the way BMS works :)
So in other words i understood that for offgrid (or ongrid) powerwall i have to buy BMS with common ports.
 
IF you skip ebike bms then thats what you Will get.
 
Common port is for systems where you have the load and charger coming from same source.

Split source /load is generally made for where you want the BMS only to cut the charger and not the load. Like Ebikes.
Or the coffee machine/lights/microwave etc. in your RV!
 
Neither BMS will cut the load when they cut the charger but the charger would no longer power the load. Consider the following diagram:


A common port BMS is better when you want the charger to power the load at the same time and requires less wiring.

A separate port BMS consume less power while on batteries as the load doesn't flow through the charge MOS (acting as a permanent diode for discharge) and that charge MOS can be smaller. OTOH if you used the load with a charger you'd switch back to batteries once the charger is cut.

So in both cases the load would always be on if you either have a battery that isn't empty or a charger connected, but powering a load on a split port BMS using a charger would be a really bad idea as you'd be constantly switching between discharge and charge (or you'd have to have another component to switch the load between charger and batteries).

I'm guessing for ebikes they use a split source BMS because you don't charge it while riding (except for regenerative braking but then that implies the only load is the controller) and you want the most out of your batteries.
 
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