It is jumping from 235 to 250 to 216 to 240, etc.. It is definitely more stable at full (255) but still over shooting some on the display. I'll try to twist the wires, but I will have to de-solder them, I didn't even think about twisting them when I made the connector. Thanks for the suggestions.
It seems to only be over shooting by 1 or 2 degrees C at 255.
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
Mine are wired in parallel, yes, I just soldered a y connector using Deans connectors to the original fan connector.
Are they not pointed at the heaterblock?
And the cool air is now coming from 2 sides. Try lowering the fan percentage to min 40 and max 60% or something.
Does that work?
No they are actually pointed away from the heater block at 20 degree angles.
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.
No they are actually pointed away from the heater block at 20 degree angles.
Do you have a picture of your printhead straight from the front?
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.
Thanks for the suggestion anon4321, I'll look into adding a cap.
Mine are wired in parallel, yes, I just soldered a y connector using Deans connectors to the original fan connector.
Can you post a picure of this?
I'm switching to dual fans but I need to resolve this issue
So far I didn't have any temperature fluctuation by the way
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.
@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?
Antiklesys, here are 2 pictures of the connection.
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.
I think the fluctuations in the temperature display might just be noise interference, as the prints seem to be printing fine.
@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.
My advice would try to twist or shield the fan wires
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.
If you want a cheap alternative in the meanwhile, you can try also using tinfoil.
That should be enough to make a Faraday cage ...and connect it to GND
mu metal (like iron) works much better than aluminum. EM waves are both electric *and* magnetic and magnetic fields go through aluminum as easily as through air. Aluminum does certainly stop the electric field though. If grounded.
I am actually using copper foil tape, the same kind used to shield guitar electronics cavities, just a lot narrower.
Either or both will work. You must ground the copper. If you used a mu metal grounding is less critical.
Should one of the ground connections on the electronics board be good enough?
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anon4321 16
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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