Phase current limits speed?

Two scenarios:

1. 60V 70A battery current 70A phase current

2. 60V 70A battery current 100A phase current

Assuming that I'm cruising at top speed meaning 60V*70A=4200W

Now my problem is with example #2 where the phase current is higher than the battery current.
The total power going from the controller to the motor cannot be higher than what the battery outputs.
So, if the current in the phases is 100A then the voltage inside the motor cannot be equal to battery voltage (60V) but has to be 42V (4200W/100A phase current) meaning that if all of this is true then I would always limit my speed when the phase current is higher than the battery current.

In practice I don't see that happening so I'm probably wrong here but I would like to know why my vesc draws 100A phase while my battery current is at 70A.

THere's a few threads here and various pages elsewhere that explain the phase-current vs battery-current thing. Difficult to locate directly in the ES search, so this is a google link instead, that lists a few right at the top.

https://www.google.com/search?q=phase+current+vs+battery+current&ie=utf-8&oe=utf-8&client=firefox-b-1

This type of schematic can help:

Also the fact that peak phase current on a sinusoidal wave is 1.4x the battery current

larsb said:

This type of schematic can help:
06FF9310-D626-453A-8ACA-ADFDF925C697.jpeg
Also the fact that peak phase current on a sinusoidal wave is 1.4x the battery current

Click to expand...

So as I thought, it ain't just a voltage number going in the motor but pulses (PWM) which makes much more sense than having a low voltage with low RPM when the current at the phases is higher than the current coming out of the battery.

Thanks for making it clear

rg12 said:

So as I thought, it ain't just a voltage number going in the motor but pulses (PWM) which makes much more sense than having a low voltage with low RPM when the current at the phases is higher than the current coming out of the battery.

Click to expand...

What makes a motor turn (provides torque) is current. When a motor spins it generates a voltage called back-EMF. You must provide more voltage than the back-EMF to enable current to flow. So, very roughly, current=torque and voltage=speed.

And since the motor cares about current, the PWM doesn't generate "pulses." It generates a given amount of current. (The windings act as a big inductor and smooths the pulses so it is continuous current.) A true sine wave controller driving at least three phases generates smooth torque with almost no ripple.

At low speeds you only need a low voltage to get a given torque out of a motor, since the back-EMF is low. To get the same current (torque) at higher speeds you need higher voltage.

JackFlorey said:

rg12 said:

So as I thought, it ain't just a voltage number going in the motor but pulses (PWM) which makes much more sense than having a low voltage with low RPM when the current at the phases is higher than the current coming out of the battery.

Click to expand...

What makes a motor turn (provides torque) is current. When a motor spins it generates a voltage called back-EMF. You must provide more voltage than the back-EMF to enable current to flow. So, very roughly, current=torque and voltage=speed.

And since the motor cares about current, the PWM doesn't generate "pulses." It generates a given amount of current. (The windings act as a big inductor and smooths the pulses so it is continuous current.) A true sine wave controller driving at least three phases generates smooth torque with almost no ripple.

At low speeds you only need a low voltage to get a given torque out of a motor, since the back-EMF is low. To get the same current (torque) at higher speeds you need higher voltage.

Click to expand...

Best explanation ever!
Thank you!

phase current is ac, battery is dc

i think you can calculate/represent power by area under a voltage/something curve graph line?

if so a good visual representation would be to compare those two surface areas (dc in, ac out)

if you can imagine...there is more surface area under the straight dc line, than a wobbly ac line.

peak, constant and average amps/volts would explain the discrepancy between the two.

i.e. 60v @ 70a dc is more power dense than 60v @ 70a ac