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Added Dual Fans now Temp Sensor Fluctuates Wildly

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It depends. By wildly do you mean changing at a rate that is probably unrealistic (going from 200 to 207 in a blink of an eye and back down to 197 in a second blink)?

If so, the fan PWM has been known to generate noise that causes the amp board to report wild fluctuations.

Is the temperature change when the fans are at 100% (255) more reasonable? If so, it is probably electrical noise causing the amp to misreport.

If it seems PWM related a few options -

Always run at 100%.

Separate the fan wires from the sensor wires as much as possible and keep the fan wires as far away from the amp board as possible.

Twist as much of the fan wiring as you can reach.

HIGHLY EXPERIMENTAL: solder a ceramic cap across the fan connector pins on bottom of the shield. This should help squelch the high frequency generated by the PWM. I've done this and it seems to help but I wasn't very scientific about it. The value of the cap I used was small, I think 0.1UF

 

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i find then the fans first come on that the temp overshoots a bit to compensate for the fact that the nozzle is suddenly being cooled :)

Not to hijack your thread - but i am about to upgrade and have a dumb reassurance question - I assume that the new fan goes on in parallel? - I am 99% sure it is a yes but just thought a sense check was worthwhile :)

James

 

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With two fans, the current draw is obviously higher. More current means more of a magnetic field which induces more noise in any nearby wiring.

Since the problem is less at 100% when PWM is nearly no longer PWM (I don't know if 255 actually just goes full on or off for 1/255th of a cycle), it is probably due to noise.

Twisting may help. If not try the cap, with a little larger value. I think it needs to be nonpolarized so ceramic is a good choice and small value ceramics are the ones always used near ICs for decoupling HF so are a good choice.

 

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I still need to do several test prints to make sure the weight does not make a difference in the print. I also just installed a custom aluminum z stage and heated bed so I am testing to see they have effected my print quality as well. After redesigning my z stage several times I made a last minute change and accidently had the holes for the adjusting screws drilled about a half inch to far back so my print surface is a little farther back than it should be.

Dual Fans

 

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Looks like very big fans! Are they the same as the electronics cooling fans?

They are more powerful then the ones on the printhead.

I think with this set up you are kinda overkilling it.

I mounted a duplicate of the fan that was already on there, and even those I need to tune down in speed or

else the temp will drop, or it will simply just blow away the filament.

I would recommend smaller (5V I believe?) fans.

 

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Looks like very big fans! Are they the same as the electronics cooling fans?

They are more powerful then the ones on the printhead.

I think with this set up you are kinda overkilling it.

I mounted a duplicate of the fan that was already on there, and even those I need to tune down in speed or

else the temp will drop, or it will simply just blow away the filament.

 

The fans are the same size as the original fan, and 12v, they are blower fans and I created a mount that has a small duct near the print head that reduces the flow through several small holes on the bottom and directs it away from the print head. With the duct the airflow is not overly strong, in fact I may make the holes slightly larger.

Here is a picture of the underside of the mount with the duct and the fan mounted. It is the same manufacturer as the stock fan and the only ones I could find that would survive the fan power supply.

12vDC Blower Fan In New Mount

I think the fluctuations in the temperature display might just be noise interference, as the prints seem to be printing fine.

 

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@3DGUY I believe you never answered Anon's very first question. How fast was the temp changing - was it something physically possible like 1 degree per second? Or was it an electrical problem where the temp might report 10 degree changes up or down in 1 second?

 

When not set to 100%, it changes every second or two, when it is set to 100% it is very stable with the temperature reading going over by 1 degree for a few seconds and back to normal and it will do this every few minutes.

 

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My advice would try to twist or shield the fan wires

 

I am going to try to shield the fan wires. I ordered a roll of magnetic shielding foil tape and another piece of the plastic spiral wire guide so I can isolate the fan wires from the other wiring, hopefully it will arrive by Thursday so I can test it soon.

 

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