2 Wire BMS

[BShady]

Hello

I was looking into getting a BMS for my 12s Battery pack but i saw there is 2 wire and three wire BMS's. i already read up on other posts about the differnece with pros and cons.

I had only one qu. For the 2 wire BMS's the load and charging are connected to the same terminal. does that mean i have to disconnect the ESC from the BMS every time i want to Charge the Batteries? To me it would seem that the charging current will flow to the ESC as well?


thanks

 

[billvon]

For the 2 wire BMS's the load and charging are connected to the same terminal. does that mean i have to disconnect the ESC from the BMS every time i want to Charge the Batteries?

No, it handles that just fine.

 

[BShady]

For the 2 wire BMS's the load and charging are connected to the same terminal. does that mean i have to disconnect the ESC from the BMS every time i want to Charge the Batteries?

No, it handles that just fine.

can you explain how it does that?

 

[amberwolf]

Current does not flow to the ESC, unless it's under load.

Voltage will be across the ESC anytime the battery is connected, whether it's charging or not.

Charging voltage shouldn't be any higher than the fully-charged battery voltage, as long as your charger is set correctly, and nothing bad will happen, and all you need is a Y-connector to plug in both the BMS and ESC to the battery at the same time.


If your charger is higher voltage than it should be, then the ESC *will* see that higher voltage whenever the BMS shuts off as cells balance and hit HVC.

If the charger is higher voltage than the ESC is rated for, it could damage the ESC when the BMS shuts off.

 

[BShady]

of course!! you need a load!!

Amberwolf thank you.

 

[billvon]

can you explain how it does that?

Say you overcharge your pack. BMS disconnects the battery from the terminals. The voltage on the terminals now shoots up to whatever the no-load voltage of the charger is. The BMS senses this and remains disconnected.

You now remove the charger from the pack. The BMS senses the voltage drop on the terminals and reconnects the battery. (Sometimes you need to pull a tiny load to get the terminal voltage down before it will reset.)

Now you overdischarge. BMS disconnects the battery from the terminals. The voltage on the terminals now drops to close to zero due to the load. The BMS senses this and remains disconnected. Once the load is disconnected the voltage rises and the BMS reconnects the battery. (Again, sometimes you need to attach a charger to get the terminal voltage up before it will reset.)

 

[BShady]

Billvon

i understand how the BMS works but i was asking (amberwolf answered) if the charger will damage the ESC as it is also sending voltage to the ESC directly on a 2 wire BMS. My problem was answered by amberwolf.