Batterypack discharge

Peter's picture


Joined: Jul 31, 2019

Replies: 0
Batterypack discharge
July 31, 2019 - 7:30pm

Im having problems with a batterypack i have build. The batterypack is a 20s (72v) 18650cells.

The problem is when is use it on my project, the voltage Will drop Real low (But only from the bms) the voltage directly from the batterypack is still High. The voltage from the bms rises again and matches the pack. (Without charging)

Anyone Got any idea What the problem might be ?


Aswinth Raj's picture


Joined: Aug 16, 2016

Replies: 950
Your Battery pack is not able to deliver enough current
August 2, 2019 - 10:28am

You have considered only the voltage rating of your battery pack. What is the Ah and C rating? Say if your battery pack is rated for 72V 4Ah with a C rating of 2. then it means your battery pack can only deliver a maximum of 8Amps (Ah rating * C rating) to your loads through BMS. Suppose if your load is drawing more current from the pack your battery voltage will collapse meaning it will drop to a very low value. 

When you remove the load no current will be drawn and hence the voltage will return back to normal. This problem gets worse when you are powring a motor, because you have to make sure your battery pack can provide enough starting current required by the motor, this starting current will normmaly be high than the operating current of the motor.