Unhandled heater runaway due to a faulty heatblock
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Hi! I am running on Duet3 6HC + 3HC.
I'm not sure if there is a way to fix this odd situation but I wanted to get the information out.I have received a new beta hotend for testing and the heater cartridge is electrically connected to the heatsink.
My heatsink is by design electrically connected to ground, for ZTATP implementation on a toolchanger.When I turned on the printer the +24 on from the heater cartridge went trough the heatsink and my ground wiring thus connecting and not being able to stop the heater.
My hotend is connected to Out1 on a Ext3HC and the ground on the heatsink is connected to ground on IO6. The boards share ground between them.
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As far as i know is this a bad idea! because the PWM Signal for the heater is the GND line. You have now connect your hotend directly to 24V so it heats up uncontrolled....
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Slam is correct. PWM is switched on the ground/- side for the Duet, so you have essentially connected the hotend directly to 24v.
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@phaedrux I know, that's the problem...
ZTATP needs the heatsink connected to ground for it to work. I now disconnect it when connecting the heater.
But there may be all-metal printers that could encounter such a problem. Or if in the middle of the print the heaterblock gets damaged.
I try to foolproof my machine as I am doomed to make all possible mistakes. -
@typqxq I thought for ZTATP, it's the touch plate that's grounded, not the nozzle? Does seem a bad idea to try and use two systems which put power signals though the hotend metal work though...
Did the Duet recognise the issue and flag a fault? Maybe it wouldn't monitor it if the heater was meant to be off?
Even if it did recognise it, the only protection it could use would be to shut down the 24 PSU in this case. I have my Duet WiFi set up to do this using a relay and the PS_ON pin. It will shut down the power supply if the heater faults. I then have a separate 5v supply to the board so the processor stays up and I can clear the fault etc and carry on
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@engikeneer Not sure what would've happened if I'd get 24v on IO_IN.
I will definitely wire in a relay on PS_ON. -
Wow, that is nasty!
I would think the heater cartridge is defective with the internal heat coil touching the case. It is an interesting reminder how shit can go pear shaped real quick!
If it is by design than the heater better have a great big warning on it as I don't recall ever seeing a heater connecting to ground through the case. It actually makes no sense (at least to me) because by the very nature the casing to ground connection isn't necessarily a good connection. -
@typqxq said in Unhandled heater runaway due to a faulty heatblock:
and the heater cartridge is electrically connected to the heatsink.
What's the point in that? Better thermal conductivity? Seems to me, the new hotend isn't compatible with the major market...
