How many phase amps can I pull from my battery? (continuously)

[Silentsniper]

I have a 72v lithium ion battery capable of giving 360a continuous and I have a plenty powerful controller and motor. How many phase amps can I pull from the battery continuously? I’ve heard many mixed answers and I just want to make sure I won’t blow anything up.

 

[calab]

Its a ratio that the controller splits into that you can control in its software bio's for the controller.
Your battery states sony blahs are 18650, 3,000mAh, 10a continuous and 20a maximum for 20 seconds.
You have 10s4p of sony blahs, thats 36v 40a cont or 80a max for 20 seconds, you set your controller accordingly.

The highest you could set, would depend on the motor is my best guess. Like you dont see many 1T motors, only 2.5 or 3T motors, so theres got to be a limit, perhaps you hit saturation or other guess of mine.

 

[amberwolf]

I have a 72v lithium ion battery capable of giving 360a continuous and I have a plenty powerful controller and motor. How many phase amps can I pull from the battery continuously?

None.

The battery current and the motor (phase) current are separate sides of the controller; the controller's job is to convert one into the other as needed. There are different ways this works within various types of controller design; see Notes at end of post.


So phase amps are pulled from the controller by the motor, limited by the controller in one of a few possible ways depending on the specific controller design, to protect both the motor and the controller's FETs.

The controller pulls battery amps from the battery, so you set the controller's *battery current limit* to whatever you need that is safely within the battery's current limits.

If the controller's battery current limit is specified as it's continuous limit, then you would set it to safely within the battery's continous current rating.

If the controller also has a peak battery current limit, then you can separately set that to ensure it does not draw peaks from the battery beyond the battery's peak current rating, and if it has a time limit for those peaks, you set that so it doesn't draw the peak longer than the battery can handle.



Then you setup controller phase amp limits to not allow the motor to draw more current under worst-case loading than the motor itself can handle (and the wiring and connectors between the motor and controller), while still giving you the performance you need.



Notes:

Basic controllers, including most typical cheap ebike/scooter controllers, only measure battery current, and only have a battery current limit. Some of them allow you to change that limit in a setup program or display, most don't.

They cannot measure phase current, so they can't limit it either. They may have a (possibly programmable) ratio between battery and phase current, so that they can guesstimate what phase current is, to attempt to protect the FETs and possibly the motor, but they can't tell what is actually going on at any moment.


Advanced controllers, including typical FOC controllers, actually measure phase currents to the motor, and have phase current limits you can setup within the controller.

They may *also* have a separate battery current measuring device and battery current limit, or they may only calculate the battery current based on a (possibly programmable) ratio from the phase current they measure (sort of the reverse of the basic issue).


The phase current limits are for protecting the controller and motor.

The battery current limits are for protecting the battery.

 

[liveforphysics]

Nailed it Amberwolf.

The pack never sees whatever the phase current may happen to be. You can have 850Amps phase current to the motor for 10Amps of pack current or less while the motor is at near stall speeds.