Hot end temp problems

Hi all again

another problem I have just encountered.

After a number of successful prints my hot end temprature is now playing up.

Firstly as it warms up it does it very quickly in jumps of 9 - 10 degrees. (Before it would take a lot longer)

When it hits its desired temp (say 185) the next 3-4 readings jump up suddenly to around 200 - 300 degrees, (before it would plateau and stay within 5-6 degrees), this then (I think) causes the heater to switch off due to high sensor readings, the readings then drop back to around 180 and progresses downwards at a sensible rate.

The temp sensor unit seems OK as when I test the warming up of a soldering iron everything goes in a logical sequence

I have reloaded the firmware but still the same problem.

I have read that it may be due to to much current being supplied to the hot end ?

But I haven't fiddled around with much as of late except for the power lead which I diconected and reconnected a couple of times (could this be a clue?).

I am running ramps 1.2 with arduino mega 1280, with a thermcouple.

Any suggestions where to look.

Thanks Again

what is the resistance of your heating element?

Sounds like the thermister wires might be shorting

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Experimenting in 3D in New Zealand

I have had this exact same problem. I checked out the thermistor and mounting and found it all OK. It must be interference in the leads or electronics somewhere. Moving your machine, rerouting wires, changing power supplies and leads can cause this problem which is I think what caused my issues.

I was getting the reading fluctuate high so the hot end switching off mid print ruining parts as it strips the filament in the pinch wheel.

I solved it by switching on "smoothing" in the firmware which wasn't set on by default. It works really well and you can see the difference when you are warming the machine with the reported values on the PC.

You could also switch off the hot end over temperature facility or set it to a higher value in firmware, or try shielding the wires somehow.

As an additional safeguard. I wrote a little routine in the code that reports the bed and extruder temperature back to the host PC at the start of every new layer (About 3 lines of code + 1 variable). This way if you came back to the machine and the print had failed you have a log of how the machine was doing. This enables you to diagnose faults more easily.

I've got similar problems with my hotend.

Heats up well but drops to 200 before it starts to print regardless of my settings in pronterface, and hot bed reads 357 degrees but cold to touch.

Have to check the thermistors.

Also I have seem some hot ends with a resistor at either end of the alloy block. Does this help?

I solved it by switching on "smoothing" in the firmware which wasn't set on by default. It works really well and you can see the difference when you are warming the machine with the reported values on the PC.

You could also switch off the hot end over temperature facility or set it to a higher value in firmware, or try shielding the wires somehow.

As an additional safeguard. I wrote a little routine in the code that reports the bed and extruder temperature back to the host PC at the start of every new layer (About 3 lines of code + 1 variable). This way if you came back to the machine and the print had failed you have a log of how the machine was doing. This enables you to diagnose faults more easily.

How do I change these settings?

Thanks

Edited 1 time(s). Last edit at 04/29/2012 07:45PM by gregted.