continuous battery amp output

[Freshblood]

Hi,

I have a question about continous amps output. For example, some batteries output about 5amps continous and with 6 in parallel it makes sense it has a 30A continous BMS. What if the batteries had 20A continous with 6 in parallel. This would be 120A continous. Could I use a 30A BMS or MUST the BMS match the 'potential' continous amperage of 120A? My motor is a 1000W and battery pack is 37V. The motor can never draw more than a 1000W so it will never draw more than 1000/37 = 27amps? Right? This means a 30A BMS would be sufficient?

What is the pros and cons here?

 

[harryS]

The watt rating on the motor is mainly for how much power it can handle continuously. It's the controller that determines how much power your motor gets. For example, I own some 250W motors, and my 20A controller will give short term power input of 600W on 36V on my LCD, and over 900W on 48V.

Designers usually size the current rating of the BMS to match the maximum current rating of the batteries, as a form of protection. It would be wasting the potential of 6 cells in parallel capable of delivering 60A by using a 30A BMS.

In general, you pick a controller to match the motor power and use a battery that can deliver that current. Still, you can do whatever you want.

 

[Freshblood]

That s interesting that you can almost quadruple your motor power for short bursts... I am building a battery and like to use the decent 18650, HG2's. They are 3000mA, 3.7V batteries. To give me a decent VA ratio I am opting for 10s6p setup. This gives me 37V and 18Ah which is perfect. It however gives me 120A continuous possibility. 20A per cell. I dont want to overheat controller or burn out motor however. I guess the motor only sucks what it requires so if it needs only 30A in total then it will only take that and the other potential will be just lost. Batteries life will be extended as we arent pushing batteries to there limit.

 

[harryS]

The continuous rating of your BMS usually refers to the safe current rating of its transistors. It can still also allow large current spikes, and the over current limit is much higher than the continuous number. You could probably pull 40A out of a 30A model continuously and the transistor would get too hot.

Wow. 30A out of a little 18650 cell. I thought 20A was super. I think you'll have a great battery when you build it.

 

[Freshblood]

Thanks. the pack could pull 120A continously as it is rated at 20A/battery and I have 6p setup. Getting too great-a-batteries is overkill I think as I will never use it.

I used the 30A in total from the battery pack only as an example. Some pack have 5A continuous 18650 and with 6p will make 30A