MK3 heatbed cannot reach target temp

Hi,

I have just purchased a MR3 heatbed (3,5 mm Aluminium one !! ), I run Ramps 1,4 on Arduino MEGA. It can reach about 63 deg C and not more. I have put foam insulation under the heatbed, i have connected the cables to 1+ and 2-. (If i connect + to 1, and - to 2&3 the board will disconnect after a few seconds.) Cables should be thick enough and they are not getting hot. Have capton tape on the alumium surface. a) I have tried hairspray = warping. b)I have tried to clean surface with acetone = warping, c)have tried abs/acetone solution = warping. All with 63deg C heatbed and ABS set to 220 deg C.

Does anyone have an idea why the heatbed cannot reach target of let us say 100deg C ? i have a feeling that that might solve the warping issue if the bed temp goes up.

Wang Fei

Sounds like you are putting power (at 12V?) onto half of a dual power heatbed, (and you get a disconnect by putting insufficient power into both halves) See [reprap.org]

Hi DaveX,

I connect according to this [reprap.org] (Even my one is a Mk3 the schematic on it is the same as this).

I am using a hacked PC powersupply of 420 Watt. Inside the powersupply was a total of 6 cables for 12 volt from the pcb. I have connected 3 together with a much thicker cable, which again is connected to terminal. Other 3 connected in same way to other terminal.
Do you mean that the powersupply is too small ?

According to the link you posted, Pin 1 is ground, pins 2 and 3 are positive.. Dunno if that will make a difference?

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_______________________________________
Waitaki 3D Printer

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wangfei
Hi DaveX,

I connect according to this [reprap.org] (Even my one is a Mk3 the schematic on it is the same as this).

I am using a hacked PC powersupply of 420 Watt. Inside the powersupply was a total of 6 cables for 12 volt from the pcb. I have connected 3 together with a much thicker cable, which again is connected to terminal. Other 3 connected in same way to other terminal.
Do you mean that the powersupply is too small ?

I think the power supply is too small -- If you try to pull too many amps, I think it shuts down and resets to give you the disconnection. If you can hook the power supply's 12V up directly to the heatbed, bypassing your electronics, can it deliver a full ~10A and heat the bed? If you are just hooking up to 1&2, you are only powering half the bed, and probably only drawing ~5A.

The polarity should make no difference, because you are using the traces on the heatbed as a resistor, and they do not care which way the power goes.

The usual words come to mind: multimeter to measure bed resistance, look for a short caused by a mounting screw, etc.

Per the link above, "resistance between 1.4 and 1.6 ohm for the 12V" .....

Edited 1 time(s). Last edit at 04/23/2014 07:41PM by vreihen.

Hi everyone,

Many tks for the different advices.

DaveX pointed out that the powersupply was to small. YES. I did connect a spare other PC powersupply directly to the heat bed and with connection to 1,2 and 3. Result was a stable temp. increase to 95 degC at first test which was enough to confirm your idea.

And to vreihen : i did measure a resistance of about 1,6 ohm so this should be ok.

So after making above to simple tests i did buy a new PC power supply and hacked it the way i had done before (seen on Youtube). I did buy a 500W. (see image of label here on attached file).

Result is that my Mk3 heat bed now can reach about 105 deg C in about 18-20 min. It does not seem to be going higher, but print tests has proven to be almost warp free. So i consider this issue to be solved for now. (I am currently printing 100x 20 mm parts which seem to be 100% warp free)

So once again thanks for all the advice and i hope this will help others with same or similar issues.

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wangfei
...
Result is that my Mk3 heat bed now can reach about 105 deg C in about 18-20 min. It does not seem to be going higher....

Is this time common/normal ??

Nope. I get to 110c in about 10-15 minutes