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dlundgren

Back fan voltage drop problem

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Hi

I am experiencing some problems with my back fan on the heater head. I have read on the forum that the back fan should always be on, but mine is never on. So, I started to measue the voltage.

The back fan is a 5V fan so I assume I should read a 5V current on the connectors to the fan. Problem is, I only read 2,5 V. But this is when the fan is connected, if I disconnect the fan and measure on the connector directly i get a nice 4,9V reading.

Anyone has any idea why the voltage drops to half when I connect the fan?

I have also tested the fan with external power source, it really needs approx 5V to start, so mine 2,5V is not enough

Best regards

Daniel

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A year or two ago they changed the circuit board it so the fan now only comes on when the nozzle is above 40C.

 

thanks for the reply gr5

Yes, i know, and when I measure the current it is 0V when the machine is of (obvious) and 5V as soon as I start the printer (with the fan disconnected). Problem is when I connect the fan (the connectors on the cable above the printhead) the voltage drops to 2,5V which is too less to start the fan

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The circuit that turns the fan on at 40C appears to be purely analog. It doesn't turn it on instantly but gradually between 38C and 42C. I suspect a transistor. This would agree with your measurement of 2.5V at 25C.

however if at 50C the 3rd fan still does not spin then I would look over the schematic. Unfortunately the newer schematic with the fan circuit is in schdoc format (altium?) and the Altium software has a free trial but is not free. Too much trouble for me to convert to an image at this point. It's fine to just short the 2.5V line directly to 5V and let the fan be always on. That's how my (older) UM2 works. Although the older UM2 also has a much quieter fan.

https://github.com/Ultimaker/Ultimaker2/tree/master/1546%20ultimainboard%20V2.1.4

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The circuit that turns the fan on at 40C appears to be purely analog.  It doesn't turn it on instantly but gradually between 38C and 42C.  I suspect a transistor.  This would agree with your measurement of 2.5V at 25C.

however if at 50C the 3rd fan still does not spin then I would look over the schematic.  Unfortunately the newer schematic with the fan circuit is in schdoc format (altium?) and the Altium software has a free trial but is not free.  Too much trouble for me to convert to an image at this point.  It's fine to just short the 2.5V line directly to 5V and let the fan be always on.  That's how my (older) UM2 works.  Although the older UM2 also has a much quieter fan.

https://github.com/Ultimaker/Ultimaker2/tree/master/1546%20ultimainboard%20V2.1.4

It sounds like the transistor can be the problem then. The fan does never come on, no matter what the temperature of the heater head is.

How do I short the 2,5V line directly to the 5V line? I dont have Altium..

I assume I do it on the main board?

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I didn't install altium either, sorry. Maybe an electrical engineer can answer this...

Well I suppose if you can find the correct voltage you just bring it over to one of the 2 fan pins - one fan pin should be ground and the other is probably a half volt or so above 0V or maybe floating.

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Problem solved:

Turns out that a relay/transistor (not sure which) on the circuit board was broken, so unloaded it worked fine, but when loaded with the fan it could not provide sufficent voltage.

Anyhow, solution was to just replace the whole circuit board (easier than soldering) and now everything works fine!

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