Okay. It’s just over the years I’ve seen many “little tests” go sideways because of being casual with power supplies.
Agreed. I was sitting over this at least 2h before posting Noctua 4-pin PWM fan speed control - #32 by hcet14 
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Hey guys, thanks for the input and the time you are investing in this topic!
Unfortunately I don’t have another “clean” power supply for 5V but I think the 24V PSU should be a good one, no?
So maybe I can use the 24V output with another buck converter to get my 3.3V in a “cleaner” fashion?
Btw I have two other questions:
- What exactly do you mean by “clean” power supply? Are you talking about the steadiness of the 5V that can only be measured with an oscilloscope?
- What is the diode actually for? For me it looks like it’s blocking the tacho signal from being read by the input pin… Or is it just a precaution that will be removed after everything is verified safe?
I will make a new wiring (maybe with a breadboard?) and post a picture here so you guys can check if I messed up something.
Hopefully I will be able to do this tomorrow and if not, definitely next week!
Don’t give up so quickly!
Stupid me, you still have your defect SKR Mini E3 v3.0?
Take the 3.3V from there.
Maybe this will answer your questions?
Hey there again! Sorry for not answering all that time but here I am again.
I did a new measuring setup with the broken SKR Mini E3 as a 3.3V power source (although it only gives about 3.1V).
The measuring setup looks like this:
This is what I measured:
5 to GND: 1.38 V
6 to GND: 3.06 V
7 to GND: 1.40 V
8 to GND: 3.06 V
For No. 8 I realized I did it wrong after I took the photo so i did an extension and measured up on the cable but there was no difference. In fact, I even measured the same voltage when the cable wasnt even connected to the 3.3V power-in channel.
When I turned the power supply on, the fan was turning at full speed.
I noticed something funny that I could not explain:
When disconnecting the 3.3V power supply the fan RPM slowed down and I measured the following:
5 to GND: 1.38 V
6 to GND: 2.10 V
7 to GND: 1.40 V
8 to GND: 2.10 V
Sooo… Any ideas?
I’m not sure what you are trying to measure, but you cannot measure neither the PWM nor the tach signal with a digital voltmeter. For any meaningful measurement, you would need to use an oscilloscope.
Having said this, I strongly urge you to seek professional help. This whole setup is homicidally negligent. Also see Working with Line Voltage (110 V / 230 V / >50 V)
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I simply measured what @hcet14 suggested here.
Might be worth to read the thread to understand why the measurements were made.
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This is beyond Klipper support and any advice given here that results in such experiments without understanding any of the implications is nothing we will support here.
Thread closed.
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