Kossel 2020 MK3 round bed suddenly won't heat beyod 60

I'm having a problem with the MK3 heated bed of a Kossel 2020 from Folger. After 2 months of light use, the bed will not heat above 60. Previously Ive heated to 100 or 110. Slow to get there but it got there!

Others appear to have a similar issue. Ramps 1.4, Marlin LCD, Inductive bed level.

Any one have a thought on this?

Edited 1 time(s). Last edit at 06/17/2015 12:49PM by siwek.

What have you done so far to find the cause?
-Olaf

Thank you

1. Reloaded Marlin multiple times
2. Power cycling
3. wiring check
4. Voltage at PSU outputs
5. Checked and resoldered thermistor (100 kOhm)
6. Signaling bed to heat every way I could find (Pronterface, Simplify 3D, LCD screen control.
7. Preheat bed to 80 with heat gun.
8 Measure bed resistance (nominal)

Just don't get it.


The interesting thing is that last 4 weeks it has been fine. up to 110 (slowly). When I was printing my office was VEYR warm (80). I wonder if that was the thing.

On possibility is that the 5V regulator on the Arduino overheated (which is a common problem), causing the voltage on the 5V rail to be significantly lower than 5V. Coupled with the fact that most RAMPS boards use unsuitable mosfets, this would cause the heated bed mosfet to pass less current than normal and run very hot - which is something you can check.

It's a real shame that most printer kits - especially deltas - are let down by cheap Arduino/RAMPS electronics.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Check the 5V from arduino and the MOSFET temperature.
Maybe the FET doesn´t switch ON fully?
Overload on the Arduino-5V regulator...?
-Olaf