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rcg3d
(@rcg3d)
Active Member
Reboots when bed heats

Every time the bed heater kicks in the system reboots.  I've purchased a new bed after measuring the resistance on the old bed which showed slightly below specs, but the new bed has the same measurement (chalk it up to my meter) and it still reboots when the heater kicks in.  It does not do this with the bed disconnected.

Any other ideas before I decide to purchase a new board?  I've already reseated all connections on the board.  

 

I *could* flash the firmware, I suppose.  I already have the MK3S+ upgrade kit and was only waiting for the new bed to arrive before I upgraded this printer.

Posted : 06/10/2022 5:25 pm
RandyM9
(@randym9)
Reputable Member
RE: Reboots when bed heats

Have you checked the voltage to the heater with the wires disconnected?

Have you checked the fuse? 

Seems very odd for a new bed/new heater to give you the same error as the old. How long has the printer been running properly?

I would reach out to Prusa support. Login to your online account and look for the ‘chat now’ button on the bottom right of your screen. You may have to disable ad blockers if it doesn’t show up.

Good luck.

Posted : 06/10/2022 8:38 pm
Zbigniew Trzepizur
(@zbigniew-trzepizur)
Trusted Member
RE: Reboots when bed heats

+1 for checking the voltage. Faulty PSU that cannot keep with the current demand which results in voltage drop causing MCU reset would be my first suspect before anything else.

Posted : 07/10/2022 9:57 am
rcg3d
(@rcg3d)
Active Member
Topic starter answered:
RE: Reboots when bed heats

Both heater outputs run at 24VDC when turned on with the heaters disconnected.

Posted : 07/10/2022 11:30 am
rcg3d
(@rcg3d)
Active Member
Topic starter answered:
RE: Reboots when bed heats

 

I didn't notice any issues with the voltage, but I should be able to swap PSU's with another printer as soon as one of others is finished with it's current print job.
 
Posted by: @zbigniew-trzepizur

+1 for checking the voltage. Faulty PSU that cannot keep with the current demand which results in voltage drop causing MCU reset would be my first suspect before anything else.

 

Posted : 07/10/2022 11:31 am
Zbigniew Trzepizur
(@zbigniew-trzepizur)
Trusted Member
RE: Reboots when bed heats

And that's why your measurement means nothing. Common failure mode for power supplies is the voltage drop under load.

Posted by: @rcg3d

Both heater outputs run at 24VDC when turned on with the heaters disconnected.

 

Posted : 07/10/2022 11:33 am
RandyM9
(@randym9)
Reputable Member
RE: Reboots when bed heats

 

Posted by: @zbigniew-trzepizur

And that's why your measurement means nothing. Common failure mode for power supplies is the voltage drop under load.

Posted by: @rcg3d

Both heater outputs run at 24VDC when turned on with the heaters disconnected.

 

True enough. Since the printer reboots when the bed heater is called (I think) he would have to bypass the Einsy board and wire the PSU directly to the bed heater (preferably with an inline fuse) to check voltage under load.

If the OP has another PSU to try, that should provide the answer.

Cheers

Posted : 08/10/2022 4:31 am
Zbigniew Trzepizur
(@zbigniew-trzepizur)
Trusted Member
RE:
Posted by: @randym9

 True enough. Since the printer reboots when the bed heater is called (I think) he would have to bypass the Einsy board and wire the PSU directly to the bed heater (preferably with an inline fuse) to check voltage under load.

If the OP has another PSU to try, that should provide the answer.

Cheers

Agreed, at this point, the most sensible thing is just to try another known good PSU given the OP has one. If it wasn't for that, I would recommend just hooking the multimeter to one of the PSU's outputs (they're in parallel -> both are the same) and just watch the voltage as the printer goes through its motions and begins to heat up the bed. It helps if the meter has a MIN/MAX feature buf if it's fast enough (or has a bargraph) you should be fine just watching it closely. I wouldn't recommend hooking a heating element meant for PWM operation straight across the power supply. While the heated bed should be fine for a few seconds, if you tried this with a hotend for example, things could go pretty ugly pretty quickly. To see how powering the hotend heater cartridge at 100% duty cycle ends up, see this thread.

Posted : 08/10/2022 8:51 am
RandyM9
(@randym9)
Reputable Member
RE: Reboots when bed heats

Agreed, at this point, the most sensible thing is just to try another known good PSU given the OP has one. If it wasn't for that, I would recommend just hooking the multimeter to one of the PSU's outputs (they're in parallel -> both are the same) and just watch the voltage as the printer goes through its motions and begins to heat up the bed. It helps if the meter has a MIN/MAX feature buf if it's fast enough (or has a bargraph) you should be fine just watching it closely. I wouldn't recommend hooking a heating element meant for PWM operation straight across the power supply. While the heated bed should be fine for a few seconds, if you tried this with a hotend for example, things could go pretty ugly pretty quickly. To see how powering the hotend heater cartridge at 100% duty cycle ends up, see this thread.

Understood and totally agree.

Posted : 08/10/2022 2:50 pm
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