Problems with Heaters
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@tomf Thx for the details. Looks like the initial procedure involves more steps than subsequent trials:
If the printer's been switched off for a long period (more than 2 hours), the temperature rises normally and is steady. I then switch on the bed (60C) and that is also steady. When I try to do anything (extrude material, home axes typically) the problem then happens, as seen in the temperature plots.
Please perform two tests with this scenario:
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Can you omit the step of heating the bed? Does it make a difference?
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Instead of homing the axes (which, if I understand you right, provokes the error), try to move the wiring harness for the print head into different directions: does that trigger the error, too?
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@dc42 said in Problems with Heaters:
@tomf I suggest you replace both the hot end thermistor and the hot end heater cartridge. I think one or both of them have an intermittent short between the element and case when hot. I assume you have already checked the hot end thermistor wires for possible shorting.
I agree that the problem could be the thermistor or heater (or maybe the Duet). Unfortunately I don't have these as spares and although I've ordered replacements, they will take about 3 weeks to get here. So I would like to confirm that somehow in case there's something else going on. The hotend heater measures 12.5 ohms, and the bed 25 ohms.
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@infiniteloop Will do when I get back later.
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@tomf said in Problems with Heaters:
The hotend heater measures 12.5 ohms, and the bed 25 ohms.
So I can assume your PSU has 24V, and your bed is not powered from mains?
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@infiniteloop said in Problems with Heaters:
@tomf said in Problems with Heaters:
The hotend heater measures 12.5 ohms, and the bed 25 ohms.
So I can assume your PSU has 24V, and your bed is not powered from mains?
Yes, 24V supply, but the bed is mains powered,120V, 600W, through SSR.
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@tomf said in Problems with Heaters:
Yes, 24V supply, but the bed is mains powered,120V, 600W, through SSR.
Good to know.
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Following up:
The spare parts arrived yesterday and today I replaced just the hotend thermistor. That seems to have resolved the problem as I did about 6 hours of printing with no events. Yipee!
I remain unclear how a faulty hotend thermistor could have had consequential effects on the reported bed temperature as shown in the chart (from the original problem) so any celebrations might be premature, but no such problem today.
