Heated bed random turn on

I've added a heated bed this weekend, I warm it up at the start in the host, then turn it off before printing. Several times while printing and sometimes at rest at random intervals , the bed turns on, and since my psu isn't quite up to the job, it trips out, killing the job, also crashing the host. I have to shut down the host and restart.

Regards
Paul

That sounds bad!

I have some problems understanding your description. What is a PSU? And how can that PSU kill a job?

The control code for the heated bed is quite simple. It reads the current temperature and if currentRepetier-Software - the home of Repetier-Host (Windows, Linux and Mac OS X) and Repetier-Firmware.
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Sorry, PSU is the power supply unit, in my case an underpowered ( since ive added the bed) ATX one which can't handle powering everything at the same time. I assume that turning off the bed in host should mean it is turned off throughout the print, since I don't think slic3r sets the temp. My problem is that it turns on during the print by itself, which trips the power and resets everything killing the job. If it is only me it must mean its a problem with my electronics which I haven't seen, because I've never used that section before.

Cheers
Paul

Ok, I understand your problem.

So the big question is why gets the heated bed turned on. Have you already tested, if the temperature reading is stable? It's the only obvious reason I can think of.

At which time does this normally happen? With hot heated bed or after it is cooled down? The NTCs are are very sensitive in lower temperature ranges making wrong temperatures mor likely. If this is the case, setting target temp. to -20 could probably help. The default for off is 0, so you would get an additional safety margin.

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Ok, I will try to check that the wiring is ok, as the ambient temperature is very low at the moment so I will try and set the target temperature lower,
thanks again
Paul