brushless 24VDC motor controlled by IRLB8721 MOSFET

Goodmorning to everyone.

I’m trying to control an brushless air pump with a MOSFET. I’m gonna decribe you the sutup and then explain the issue.
In the attachments there is the circuit pic.

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After I gave you all the infos (I hope), here is the issue: when using the motor at higher PWM (from 45 to 100), no problems at all. When I’m turning to lower PWM levels (under 30), the Power Supply tells me than I’m going to Amp Limitation (I can set the maximum amps supplied by the PSU).
it’s quite strange: maximum ampere usage of the pump is 3.4 Amp, and I set the map amps at the PSU at 5.28Amps.

I think I’m missing something about MOSFET behaviour. I’m quite sure of that.

Unfortunately you haven't given us any information about whatever it is that you're trying to control. Most brushless motors don't even have a "negative pole".

Steve

sorry, you're right.

I'm trying to control rpm of a Hydrogen pump; this pump is driven by the brushless motor I mentioned; here is the link to the pump datasheet ( https://aldax.se/wp-content/uploads/2012/06/T2-01%20Data%20Sheet.pdf ). It's the brushless one.

I want to control Hydrogen flow with this pump.

thankyou very much

So your pump has 10 connections ? Are you really only using 2 of them as the Fritzy thing seems to show. Which ones?

Steve

From the PDF, this is the piece I wanted to know:

Brushless Motor
Mutli Wire Connector 24V Power, 0-5V Speed Control

The pump can be controlled by DC voltage or PWM through
a control board supplied by the customer. The minimum
recommended PWM frequency is 20kHz.

Are you using the PWM pin or the 0-5v motor control pin?

Nope, I’m just using the red/black wire of the power input, using a mosfet that scales up the pwm signal. Maybe this brushless motor is not suitable to be regulated by pwm; I used the same technique with a brushed and it worked fine.

I still cannot use the PWM wire because I’m waiting for logic lever shifter: the pwm signal require a 12V reference.
I also thought and tried to use the 0-5 Volt motor control, but it does not work.

2 of this connection are soldered together by default (the enable and the 5vdc output) so that the motor is by default working.

thankyou for the replies guys!