thermostatic fan not starting properly

I am having some issues with a fan that I have configured for thermostatic mode. I use the following command to configure it in config.g

M106 P1 T45 H1

When I set the temp of the hot end to 50, the fan turns on as expected at 45. However, when I set it to 205, the fan doesn't turn on until the temp reaches 170-190. At 170, you can see the fan trying to turn, like you have too low of a speed set. By the time it gets to 190, it is running full speed.

My understanding of the mode is that the fan should be at 100% once the temp is over the threshold, but it is looking like it might be ramping the speed up instead. I have tried other example commands, but they all act the same.

I suspect you are using a common positive supply wire to feed both the hot end heater and the fan, but you have used the heater negative terminal as the common wire instead of the heater positive terminal.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
I suspect you are using a common positive supply wire to feed both the hot end heater and the fan, but you have used the heater negative terminal as the common wire instead of the heater positive terminal.

How would that cause these symptoms? The fan still turns on, just not at the expected times. And yes, both the heater and fan use a common positive supply and are not wired as you described.

So, after sleeping on it and having time to think about how this would cause these symptoms, I checked again and sure enough, I had the connection to the hot end backwards on the board. Switching them around resolved the issue. Thanks.