Temp falls when I turn fan on??

I built a prusa mendel with ramps1.4 using Marlin.
The extruder temperature drifts a little more than I would like( if I print at 180, maybe it drifts to 177)
However I have a fan mounted and connected to D9, when I turn it on with M106 then the temp really falls off (if printing at 180 it will drop slowly(30s) to around 168 and hovers there).

Any ideas?

Now I found when I print without the fan it holds pretty good usually 178 or 179 for 180 set.
But if I connect the fan even externally, not through ramps, just jumped to power supply then the temps falls to 168C
??

It's probably that the PID values aren't sufficient to overcome the cold air being blown on the Hotend.
What firmware are you using, both Maflin and Sprinter have auto tune functions.

maybe it could be the power suply not being able to give neough current to heat up the hotend for the amount you cool it with.

are you using a 12V fan try connect it to 5 v and check then

Is your hotend insulated? That helps a lot. It is basically essential if you have a fan blowing on it.

I'm running Marlin, I'll run the M303 autotune...

PSU: [sell.pakuya.com]
its 12v, 18A PSU

The fan is 12v

hotend has thermistor taped to it. Then has 2 of those black insulator sleeves. Is that enough? or will the fan cool the thermistor/hot end? should i put more insulation?

if using a resistor heater you can use the following: just be sure the resistor wire leads and the resistor area is first wrapped around with kapton tape. the wire leads of the resistor can be 70-90deg higher than the heater block!

put on more insulation. i use wool weather stripping, the kind you staple on to doors and areas you want to insulate of your home, and it is found in hardware section of many stores. it is light and about 1/4 inch thick. then you can hold the outside together with electrical tape. it insulates so well, the electrical tape never gets hotter than the specified temp for the tape. all the metal areas should be covered up, and any part of the resistor wire leads need to be taped around and sealed with kapton tape. the resistor wires are the only part that can get hotter than the rest of the hot end, you do not want those areas exposed directly to the wool. wool flammability temp is around 570 -600 °C. so this only works if you stay below those temps. which currently for the range of feedstock should be acceptable.

here is a video that shows the wool insulation. the video is of calibration pyrimid, but you can see the insulation and the electrical tape on the outside. the hot end is one i designed, but that does not matter. look at the insulation

Edited 1 time(s). Last edit at 12/23/2012 12:27AM by jamesdanielv.