Not able to PWM for berd air pump

SM3D

Hi all,
I recently got curious about berd air cooling, I got a 24V pump and followed the instructions regarding flyback diode and current limiting thermistor. My other post in the thread shows the setup pictures:

https://forum.duet3d.com/topic/4477/24v-pump-can-i-connect-direct/8

When I connected the pump to FAN0 or FAN2 (my original dual fan set up), the pump motor did not run. I connected directly to 24V power supply and it works. I connected my fans back to check whether I blew the MOSFET or not, but thankfully I was able to run the fans with no problem, so I did not blow the MOSFET.

I connected the pump to always on Fan port in duet and the pump works fine. I suspect that I might have the wrong PWM frequency, so looking at berd air configuration post, I set the F parameter in M106 to 25kHz and it did not work. I tried 500, 100 and the original 250 still no luck.

I am not an electrical engineer but I think it has something to do with PWM frequency. I might be wrong. Can someone please help me to sort this issue. My duet version is 1.01 and I am running firmware 1.21

Cheers,
Vasan

dc42

When you connected the pump to the always-on fan connector and it ran, were the flyback diode and thermistor still in the circuit? If so then they can't be causing the problem.

SM3D

@dc42 I had fly back diode and thermistor connected all the time. The pump does not run at all when I connect to Pwm fan ports but ran fine with always on fan port. I am not sure what is the problem with Pwm control of this pump. Any suggestions would be helpful.

Cheers,
Vasan

dc42

@sm3d said in Not able to PWM for berd air pump:

@dc42 I had fly back diode and thermistor connected all the time. The pump does not run at all when I connect to Pwm fan ports but ran fine with always on fan port. I am not sure what is the problem with Pwm control of this pump. Any suggestions would be helpful.

Cheers,
Vasan

Does it work when you specify full PWM, i.e. S1 or S255 in the M106 command?

SM3D

@dc42 I was travelling and could not reply you faster. Here is the configuration for fan

M106 P0 S255 I0 F25000 H-1

I tried both S1.0 and S255 but nothing happened with PWM fans. As I mentioned, the pump works fine with always on fan ports.

What is the difference between S factor mentioned in M106 and slider used in Duet web control? Do they perform the same function.

While I am typing this my config.g got deleted automatically and I see config.g.bak. Any idea how to recover my config.g file

SM3D

Took the SD card out, renamed the config.g.bak to config.g, the duet is back online but still I have this problem with the pump

Cheers,
Vasan

dc42

@sm3d said in Not able to PWM for berd air pump:

@dc42 I was travelling and could not reply you faster. Here is the configuration for fan

M106 P0 S255 I0 F25000 H-1

I tried both S1.0 and S255 but nothing happened with PWM fans. As I mentioned, the pump works fine with always on fan ports.

What is the difference between S factor mentioned in M106 and slider used in Duet web control? Do they perform the same function.

While I am typing this my config.g got deleted automatically and I see config.g.bak. Any idea how to recover my config.g file

Does it work if you short out the thermistor? I don't recommend running it like that for long, but I recall that someone else found that the thermistor stopped the motor from starting - indicating that a physically smaller thermistor is needed.

SM3D

@dc42 I connected the positive from the pump directly without the resistor. I also tried by touching both the legs of transistor together effectively shorting them(hope I am correct) still no luck.

dc42

@sm3d said in Not able to PWM for berd air pump:

@dc42 I connected the positive from the pump directly without the resistor. I also tried by touching both the legs of transistor together effectively shorting them(hope I am correct) still no luck.

That's odd, because with the FET shorted its Fan connector is in parallel with the always-on connectors, and you said that the pump works on those (even with the thermistor).

SM3D

Yes I agree with you that its odd. I don't know what to do. Thanks @dc42 for your suggestions so far.

Cheers,
Vasan

dc42

You could use a multimeter to check for low resistance between the VFAN pins of the always-on and controlled fan connectors. Also to check for low resistance between the mosfet source pin and the ground pin of the always-on fan connector.

Then connect the pump/thermistor combo to a controlled fan output, set that fan to full PWM and not thermostatic control, switch your multimeter to Volts and measure between the VIN ground terminal and each of:

FAN- output on the controlled fan connector
VFAN output on the controlled fan connector
Mosfet source pin

Take great care when measuring these voltages! Many users have shorted the fan output pins together when trying to take similar measurements, resulting in a blown mosfet. So plan how you are going to do it with no risk of shorting anything, and do a dummy run with power off first.

SM3D

Hi David @dc42 ,
Thanks for your help and suggestions! My knowledge in electrical engineering is very limited so pardon my silly questions. I use duet v1.01, may I know where is the MOSFET source pin? I am trying to write the procedure in steps based on my understanding.

Step 1:

Check the resistance between V_FAN pin of FAN_0 and V_FAN pin of Always on Fan

Step 2:

Check the resistance between MOSFET source pin and ground pin of Always on Fan - Where is the MOSFET source pin in Duet wiring diagram

For Step 1 and 2 what are the typical resistance values?

Step3:

Connect the pump with thermistor to one of the PWM control fan pins then measure the voltage between:

(i) Negative pin of the PWM fan connector and VIN Ground terminal (-ve pin of the power input)

(ii) Positive pin of the PWM fan connector and VIN Ground terminal (-ve pin of the power input)

(iii) Mosfet source pin and VIN Ground terminal (-ve pin of the power input)

In the duet wiring diagram, if you can indicate where is the MOSFET source pin, it will be helpful.

If it involves a high probability of blowing up a MOSFET, I rather prefer not to do it because I do not have the skills to solder them back.

Thanks again for your help!

Cheers,
Vasan

Hergonoway

Same issue there, thermistor doesn't close the circuit.

I've removed it for the moment, hope not for too long

@dc42 mentionned in a another post that it may be due to the motor not drawing enough current to heat up the thermistor (Posting this to merge backlog discussion in this dedicated topic)

SM3D

@dc42 @Hergonoway The problem is solved. I reduced the frequency F parameter to 10 to see what happens and voila, PWM worked. Then I raised it to 100, still worked. I am yet to check higher frequencies (will do in the evening).

Previously, I used F25000, F500 and F100 but it did not work. Now out of the blue it works. I haven't changed anything in my setup.

Cheers,
Vasan