How does a 3 wire nozzle coolng fan work on the MK3S+  

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

5020/5015 is just the dimensions of the fan. 50mm x 50mm x 20mm or 15mm. It doesn't really have anything at all to do with any of the questions you are asking. They both come in 2/3/4 wire variants and are going vary quite a bit in performance and operation based on manufacturer, specs, voltage, etc.

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

The three wires are positive voltage, ground and rpm signal.  The speed of the fan is controlled by changing the power to the positive voltage line, usually using pulse width modulation.

Not sure why the fan wouldn't be working unless there is some current issue to the fan through the controller.  A quick search shows that for 12V fans, there is a point that the fan won't work if the PWM voltage gets too low.  You may be running into that issue with the fans you are testing with. 

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

Thanks for your reply. I'm familiar with their dimensional differences. And if it's the only difference, then what could explain that I can't run a 5V 5020 on the same set of wires that runs a 5V 5015?  I'm hoping for a more technical explanation.

Posted by: @_rob_

5020/5015 is just the dimensions of the fan. 50mm x 50mm x 20mm or 15mm. It doesn't really have anything at all to do with any of the questions you are asking. They both come in 2/3/4 wire variants and are going vary quite a bit in performance and operation based on manufacturer, specs, voltage, etc.

RE:

Thanks for your reply.  At first glance I expect the 5020 work the same as 5015 if they have the 3 wires, but these don't and I don't understand what might be different about them that could cause the different behavior.  That's why I'm asking questions here, hopefully get some help from the community.  If there's anyone with a more detailed knowledge about how these fans work, that would be great!

Posted by: @robin_13

The three wires are positive voltage, ground and rpm signal.  The speed of the fan is controlled by changing the power to the positive voltage line, usually using pulse width modulation.

Not sure why the fan wouldn't be working unless there is some current issue to the fan through the controller.  A quick search shows that for 12V fans, there is a point that the fan won't work if the PWM voltage gets too low.  You may be running into that issue with the fans you are testing with. 

 

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

Without the rpm sense wire the fan should be causing a fan error in the MK3 firmware when its powered up, this may cause the power to it to be turned off, hence not spinning at all.

You NEED the sense wire sending its pulses to the Einsy.  One way of testing to to reconnect your original fan that does spin and then connect the power wires of your new fan in parallel to the power wires of the old one.  The old fan spins and provides the feedback but both fans get the power supplied by PWM and spin.  Its a common technique on multi parts fan modifications as you should only provide 1 feedback source.

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

Posted by: @buildx

Thanks for your reply. I'm familiar with their dimensional differences. And if it's the only difference, then what could explain that I can't run a 5V 5020 on the same set of wires that runs a 5V 5015?  I'm hoping for a more technical explanation.

If you want a more technical explanation then we need more technical details. You're asking for the difference between 2 fans but you're sharing the most useless information about them. It's like asking the difference between a 2000 square foot house and 3000 square foot house. Based on that information, the only answer anyone can give you is the size.

...what could explain that I can't run a 5V 5020 on the same set of wires that runs a 5V 5015?...

I guarantee the fact that one is a 5015 and the other is a 5020 has absolutely nothing to do with it.

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

To add to this.  The idea of three or 4 wire fans is to control the speed with a feedback system.  No feedback, then the control has no idea of how the fan is working or if is working at all.  Inside a 3 wire fan is a sensor to measure the RPM of the fan so the system can control the PWM voltage to the fan and change the speed. 

FWIW, I did a quick bench test with a small 5V fan 40X40X20 with a bench power supply to see what happened when just turning down the voltage.  The fan did slow down, but not as much as I expected until the voltage hit 3.60 V and then started to shudder while spinning.  At 3.5 volts, the fan just stopped.  To get the fan going, I had to turn the voltage to 3.70V.  At 3.67V, the fan would try to turn.

PWM drives provide full 5 volts to the motor creating a larger current and thus magnetic field to drive the motor.  Just lowering the voltage doesn't generate enough current to create a magnetic field to pull motor.

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

I'm not trying to be coy or ambiguous on purpose here -  I posted the information I have to ask for help, and your claim of "useless" information is only based on your knowledge of the topic. 

If you can't help, you don't need to flame ppl for asking for help (sorry, you message came across to me as being rude).

Hoping for some insights/clues/direction to investigate - @neophyl provided some insights already that I will pursue.

Posted by: @_rob_

 

Posted by: @buildx

Thanks for your reply. I'm familiar with their dimensional differences. And if it's the only difference, then what could explain that I can't run a 5V 5020 on the same set of wires that runs a 5V 5015?  I'm hoping for a more technical explanation.

If you want a more technical explanation then we need more technical details. You're asking for the difference between 2 fans but you're sharing the most useless information about them. It's like asking the difference between a 2000 square foot house and 3000 square foot house. Based on that information, the only answer anyone can give you is the size.

...what could explain that I can't run a 5V 5020 on the same set of wires that runs a 5V 5015?...

I guarantee the fact that one is a 5015 and the other is a 5020 has absolutely nothing to do with it.

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

Posted by: @neophyl

Without the rpm sense wire the fan should be causing a fan error in the MK3 firmware when its powered up, this may cause the power to it to be turned off, hence not spinning at all.

You NEED the sense wire sending its pulses to the Einsy.  One way of testing to to reconnect your original fan that does spin and then connect the power wires of your new fan in parallel to the power wires of the old one.  The old fan spins and provides the feedback but both fans get the power supplied by PWM and spin.  Its a common technique on multi parts fan modifications as you should only provide 1 feedback source.

Thanks, that's a good suggestion.  I will try that next.

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

Posted by: @buildx

If you can't help, you don't need to flame ppl for asking for help (sorry, you message came across to me as being rude).

I was simply asking for more information on your fans other than their size. But if you think I'm being rude for trying to help then I don't know what else to say other than have a nice day.

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

Posted by: @robin_13

The three wires are positive voltage, ground and rpm signal.  The speed of the fan is controlled by changing the power to the positive voltage line, usually using pulse width modulation.

Not sure why the fan wouldn't be working unless there is some current issue to the fan through the controller.  A quick search shows that for 12V fans, there is a point that the fan won't work if the PWM voltage gets too low.  You may be running into that issue with the fans you are testing with. 

 

Thanks for your thoughtful responses! I thought that PWM regulates the pulse duration and frequency to drive the motor, not the actual voltage itself, right?  So the pulses are a step function at 5v with a certain on/off cycle. Part of your response is suggesting that the Einsy controls the fan speed by manipulating the voltage itself, below which the fan doesn't spin.  Can you clarify?

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

Posted by: @buildx

 

Posted by: @robin_13

The three wires are positive voltage, ground and rpm signal.  The speed of the fan is controlled by changing the power to the positive voltage line, usually using pulse width modulation.

Not sure why the fan wouldn't be working unless there is some current issue to the fan through the controller.  A quick search shows that for 12V fans, there is a point that the fan won't work if the PWM voltage gets too low.  You may be running into that issue with the fans you are testing with. 

 

 

Thanks for your thoughtful responses! I thought that PWM regulates the pulse duration and frequency to drive the motor, not the actual voltage itself, right?  So the pulses are a step function at 5v with a certain on/off cycle. Part of your response is suggesting that the Einsy controls the fan speed by manipulating the voltage itself, below which the fan doesn't spin.  Can you clarify?

The fan is controlled by the yellow wire and 5v red wire has the same input all the time 

RE:

Not strictly correct @Hello, with pwm speed control of a motor the voltage is always the same, in this case 5v, but the duration that the 5v is supplied as a ratio of On to Off changes. So with the fan at 100% speed the time period might be 95% on and 5% off. For 50% speed the voltage might be 5v for 60% of the time and off for 40%.  This is many many times a second, usually the pwm base rate is fast enough to take it above the audible range. If you don’t then you can get an audible whine Which is a bug Prusa has had in the past on some of their firmware. For fan off the voltage will be turned completely off.  In software there’s an internal curve graph that equates the on/off times to the speed required. 

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

"you're sharing the most useless information" = trying to be helpful? Wow.  I guess the community will decide.  It seems you haven't tried to troubleshoot a fan that's not working right before, so you find my info useless.  Funny how others have used the info to share some useful suggestions already. 

Posted by: @_rob_

Posted by: @buildx

If you can't help, you don't need to flame ppl for asking for help (sorry, you message came across to me as being rude).

 

I was simply asking for more information on your fans other than their size. But if you think I'm being rude for trying to help then I don't know what else to say other than have a nice day.

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

Posted by: @neophyl

Not strictly correct @Hello, with pwm speed control of a motor the voltage is always the same, in this case 5v, but the duration that the 5v is supplied as a ratio of On to Off changes. So with the fan at 100% speed the time period might be 95% on and 5% off. For 50% speed the voltage might be 5v for 60% of the time and off for 40%.  This is many many times a second, usually the pwm base rate is fast enough to take it above the audible range. If you don’t then you can get an audible whine Which is a bug Prusa has had in the past on some of their firmware. For fan off the voltage will be turned completely off.  In software there’s an internal curve graph that equates the on/off times to the speed required. 

Thanks for your help!

I was able to collect more info tonight.  At 240 fan setting, the fan runs fine, but I can't really hear the difference between rpm @240 and @255 (max).  starting @235 and below, the fan turns on for half a second or so, spinning a few revs, then shuts off a few seconds (4-5) and repeats.  Then after a couple of cycles, I get an error message: "cooling fan error", but it still continues on this on/off cycle, then beeps with the error message again, then the whole cycle repeats.  So it appears that the yellow wire is sending some signal to the controller, right? 

If so, could it be that due to the construction of the windings of my 5020 fans (from different suppliers), it takes more current to get it started, but by the time it starts, due to the lag in response, the signal is at zero again, because of PWM cycling, so it never really gets started properly...

If this is true, then why would a vendor sell a 3 wire 5020 fan? (rhetorical)

Or did I really buy defective fans from different suppliers?  Seems very unlikely.

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

You are correct.  The PWM represents the duty cycle of the pulses to the motor.  Just as Neophyl explained.  There is math involved to fully explain how the speed is varied by changing the Pulse Duration.  If you run the PWM through a filter, you can get a lower steady state voltage but that won't work.  The motor needs the full 5V signal.

I did a test earlier today with a 5V fan and straight DC power.  The fan would run until the voltage dropped to 3.5 volts but would start again at 3.7V.  An interesting test.  To control a fan, you need to use PWM.  There  are articles on controlling a fan with an Arduino, explaining how the three wire fan can send a signal about the RPM to the Arduino to control the speed by changing the PWM ratio if you are interested.

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

Posted by: @robin_13

You are correct.  The PWM represents the duty cycle of the pulses to the motor.  Just as Neophyl explained.  There is math involved to fully explain how the speed is varied by changing the Pulse Duration.  If you run the PWM through a filter, you can get a lower steady state voltage but that won't work.  The motor needs the full 5V signal.

I did a test earlier today with a 5V fan and straight DC power.  The fan would run until the voltage dropped to 3.5 volts but would start again at 3.7V.  An interesting test.  To control a fan, you need to use PWM.  There  are articles on controlling a fan with an Arduino, explaining how the three wire fan can send a signal about the RPM to the Arduino to control the speed by changing the PWM ratio if you are interested.

If it takes higher current to get the 5020 to get the fan started, is it possible to pump more current from the controller board to the fan? and how?

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

Posted by: @buildx

 

Thanks for your help!

I was able to collect more info tonight.  At 240 fan setting, the fan runs fine, but I can't really hear the difference between rpm @240 and @255 (max).  starting @235 and below, the fan turns on for half a second or so, spinning a few revs, then shuts off a few seconds (4-5) and repeats.  Then after a couple of cycles, I get an error message: "cooling fan error", but it still continues on this on/off cycle, then beeps with the error message again, then the whole cycle repeats.  So it appears that the yellow wire is sending some signal to the controller, right? 

If so, could it be that due to the construction of the windings of my 5020 fans (from different suppliers), it takes more current to get it started, but by the time it starts, due to the lag in response, the signal is at zero again, because of PWM cycling, so it never really gets started properly...

If this is true, then why would a vendor sell a 3 wire 5020 fan? (rhetorical)

Or did I really buy defective fans from different suppliers?  Seems very unlikely.

An interesting problem.  I do suspect it is current related but I find it hard that that small difference would have an effect.  The frequency of the PWM is in the 20-30 KHz range which is over 120,000 pulses per minute.  The fan should have a current rating on the label.  Larger fans do have a higher current rating as there is more material to turn.   The schematics for the Einsy board is online and there doesn't look like there is any real current limiting method on the board.  What does concern me and may be causing your issue is that the board is switching the ground, not the power.  I will have to look at this closer.  I would confirm the wiring for your fan is the same.  

https://github.com/ultimachine/Einsy-Rambo/blob/1.1a/board/Project%20Outputs/Schematic%20Prints_Einsy%20Rambo_1.1a.PDF

RE: How does a 3 wire nozzle coolng fan work on the MK3S+

In my searches, I can across this article that covers this discussion.  It explains the issues with switching the GND and how it affects the tach reading.  

Information on controlling fans