Fan During Printings?

Hi, I installed 40mm fan on my prusa last night and did a hollow cube test;

material abs
walls 3
bottom 0
top 1
infill 0
auto fan enabled
fan on at layer 5
min fan 35%
max fan 100%

To my concern was that, when the fan turned on, the bed temp suddenly dropped as low as 95'c when it was originally 110'c and my heated bed unable to go up again, only around 100'c max when using the fan and the cube already peeled from the bed but still printing though.

One improvement I saw by using fan is the outer surface has finer finish compared to not using fan, looks perfectly aligned. Correct me on this one if I'm wrong

Another thing is, the air blowing out of the fan duct are dispersed like a spray, the fan duct I attached is from here [www.thingiverse.com]

Here are my setup [imgur.com]

My question is, is it normal to have the bed temp goes down during fan blowing on to the prints?

The laws of physics say yes, but your power supply is probably not powerful enough if it can't even maintain the temperature after the initial drop.

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Master Tinkerer

I suppose I didn't supply enough info

electronic
29A 12V psu
ramps 1.4
e3d v6
tower pro sg9 servo
2004 lcd panel

My printer placed on living room, underneath the ceiling (not directly under it).

Last night I tried turning off the ceiling fan, nozzle is 2mm above bed positioned at the center, fan were set to full while bed heating up, it couldn't reach to 110'c. I tried using a small cardboard covering it diagonally from the front, still couldn't reach the target temp. Last night was quite cold actually probably around 25'c

I guess I need to run the bed pid?

I've been having delamination issues on attempting printing my printer's parts

I might suggest taking a peak at your firmware to see if the heatbed has maximum power output enabled. It is possible that something in the firmware is limiting the maximum temperature, or just the RAMPS output power.

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Master Tinkerer

Now I'm confused, I don't think I ever enabled bed pid in the first place. One reason I never tried to fiddle with bed because of high current involved on heating up the bed

Here is my config.h [pastebin.com] hope someone can guide me on this

line #240 is weather or not PID will be used to control the temperature. this has no effect on the current draw from the bed, so you should enable this if possible.

Also, do a M303 to autotune the bed. for example, M303 E-1 S60 C8 will target extruder -1 (the bed) and run autotune at 60 degrees 8 times (to make sure that the heat has time to disperse).

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Master Tinkerer

Okay, I'll enable the bed pid later tonight. What about the bed pid autotune, should I do the autotune before enabling the pid or after?

If after, what initial pid value should I use for autotune?

The pid value there were the autotune value returned but with bed pid disabled (I think) in the past. Seeing how the value were, it looked like somewhat extremely high value.

I'm not an electrical and electronic proficient person

You can enable bed PID without affecting the auto tune function. Make sure the bed is at room temperature before running the auto tune function. Also make sure you store the new found settings, this will not be done automatically.

These instructions are for Marlin, other firmwares may differ.

Run pid tuning, with S indicating your preferred heated bed temperature, C the number of cycles:
M303 E-1 S60 C8

The last PID values needs to be set using, replacing the values 1 2 and 3 with the corresponding values found above:
M304 P1 I2 D3

Depending on if you've enabled the EEPROM, you need to enter the values in the firmware and recompile or use M500 to store the settings in EEPROM.

Edited 2 time(s). Last edit at 10/19/2015 05:49AM by imqqmi.

Usually you don't use a fan printing with ABS.

Thank you for feedback, I enabled the pid and used the autotune at 60'c 8 cycles, values are somewhat close to before, and it's having hard time to reach 110'c when the bed is infront so I always put the bed at the back of the printer because it's shielded from stray wind from ceiling fan

@Putzer, I last night tried to print another of my printer parts but decided to increase to 260'c, the results were great this morning, the fan mostly were disabled so I guess I should disable the fan from what you said. furthermore, with fan actually, on a 20mm test cube, the surface somewhat aligned much better than without fan, this also what troubles me either to use or not to use the fan due to appearance quality improvement

in addition, during the autotune upon starting the first cycle, it state something like 34'c @ 127, from what I understand is the '127' is the amount of power driven to the bed, is this normal?

So let's say the pwm is 255 to drive the bed, does the current drawn by the bed would be the same as pwm at 127?

Edited 1 time(s). Last edit at 10/20/2015 01:06AM by sarf2k4.

If you plan to use 110 degrees more, try pid tuning to that temperature. It likely puts in more power, especially close to 110 degrees setpoint.

Just ignore the output during the tuning. If you've set bed pwm to 255 you're good.

Okay, I will try again, with my bed in front where its most likely having trouble reaching 110'c tonight

I did autotune and finally the bed able to reach up to 110'c with a little bit slow, with the bed positioned in front of the printer/Y max pos with medium ceiling fan speed, it failed due to timeout and I restarted again and it's done with the new values.

When I try to print one of the small objects, with auto cooling + always on at 25% min, the bed drops as low as around 100'c, the fan turned on at 1mm height or at 10th layer based on 0.2mm layer height

I know it's already been said, but print fans are generally not used for ABS. But that's a personal choice I suppose....
From your photo, it looks as though the heat bed is installed with the actual heating element underneath. Have you considered turning it upside down so the heated side is making contact with the glass? The way (I think) you have it, the heat bed pcb is actually acting as an insulator between the heating element on one side of the heat bed and the glass surface you print on.
Another thing you could try is putting some insulation under the heat bed. I see a lot of people put cork board underneath. I have just used some cardboard and taped it under.
Getting the heat up around 100 degrees or higher is something a lot of people struggle with. And when you put a fan on it, it will struggle further.

I didn't flip the heated bed upside down because the wire are soldered underneath the bed, but last time I did shift the thermistor to the center hole of the heated bed instead of being taped down underneath the bed (previously by supplier) and taped it using kapton tape.

I did try to put cardboard underneath it, having the bed positioned at y max, but that time I didn't turn on the bed pid yet and it still struggling. I was considering to wrap the cardboard with aluminum foil but somewhat scared I might short the bed wires together

how big is the heatbed? The ramps board may not be able to supply the current your bed needs. however, using w relay means all sorts of problems like fluctuation and inconsistent z positioning.

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Master Tinkerer

20 x 20 cm by the way

hmm.. mine is that size, but I never tried getting it up above 70.. I wonder if maybe it could actually be a 24v heatbed? did you solder the wires on yourself? this is the only thing I can think of, other that some limiting between the PSU and the pcb heater is happening in the controller.

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Master Tinkerer

I print abs with bed at 100c plus start to finish and 245c to 250c on hotend, but without a fan running between 30% to 40% from 3rd layer up there was no way my print ever finish without curling from 4th layer up, first layer is easy to me, I bought some printing paste off ebay for 8 euro, lasted 40 plus print still have more than half the pack left, I als have an enclosure made from foam pads

Edited 1 time(s). Last edit at 10/29/2015 02:30PM by deaconfrost.

Mine is 12v system by the way and it's presoldered. I don't dare to resolder the connection because of my soldering skills aren't that great

100'c is quite low for abs and will come off anytime below that point

Edited 1 time(s). Last edit at 11/02/2015 09:43PM by sarf2k4.