DRV8308: I seem to be hitting a maximum speed wall with my motor.

Reif Heck11

Intellectual 700 points

Part Number: DRV8308

Hi Adam,

The motor I am using has the following characteristics:

4 Poles
10,000 RPM Max
24 volts

I am feeding the controller with PWM set for:

332 Hz
50% Duty

This should give me 9960 RPM according to the equation:

Fclkin = (RPM/60) * (4 Poles/2)

With Fclkin = 332 Hz

RPM = 9960.

It seems that no matter what settings I try, I can only get the speed up to ~8,000 RPM.

Is this the limit for a 4 pole motor?

Thanks Adam,

Reif Heck

over 5 years ago

0 Adam Sidelsky over 5 years ago

TI__Guru 65190 points

Hi Reif,

Thanks for posting on the Motor Drives Forum.

Have you confirmed your power supply is providing 24V and is not current limited?

What happens if you increase Fclkin?

My 4 pole motor here has a max RPM of 4000 mechanically so I cannot check this at the moment.

Regards,

-Adam

0 Reif Heck11 over 5 years ago in reply to Adam Sidelsky

Intellectual 700 points

Hi Adam,

The power supply is supplying 24 volts at 300 mA. It is not current limited.

I will try to increase Fclkin and see if that does the trick. I'm using a 16 bit Atmega2560 timer to generate the PWM.

Thanks Adam, I'll let you know how it works.

Reif

0 Reif Heck11 over 5 years ago in reply to Reif Heck11

Intellectual 700 points

Hi Adam,

I tried setting the PWM Frequency all the way to 500 Hz but the speed seems to be locked at around 7960 RPM

I can see where the current jumps to ~400 mA and then quickly drops down to ~300 mA and is steady there.

I tried it with Auto Gain Disabled but it is locked @ 7960 RPM

Any other ideas?

Thank you Adam,

Reif

0 Reif Heck11 over 5 years ago in reply to Reif Heck11

Intellectual 700 points

Adam,

I also have my auto gain set point at 382 Hz.

Reif

0 Reif Heck11 over 5 years ago in reply to Adam Sidelsky

Intellectual 700 points

Hi Adam,

I was able to get to 10000 RPM by:

Setting AG_SETPT to 1000 = 763
Disable ENSINE 180 degree sine wave current drive
Auto Gain Enabled
Increasing the PWM Frequency to 400 Hz.

There is some slight jitter but it is very stable and running at 310 mA.

I'll try the motor tuning next.

Thanks Adam,

Reif

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DRV8308: I seem to be hitting a maximum speed wall with my motor.