Duet Maestro Bed heating uncontrolled
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@NTX9 said in Duet Maestro Bed heating uncontrolled:
Prior to this fault, I had an issue with the hotend thermister. It was throwing inaccurate readings and may have been shorting. Could this have damaged the mosfet?
No.
If the mosfet has failed, this seems like a extremely problematic issue. The amount of power being applied to the bed seems like a tremendous fire hazard.
That's why I always advise users to either select a bed heater that can't get to a dangerously high temperature even when run at full power for an extended period of time, or to fit a thermal cutout to the bed in series with the bed heater. I have a Crane Quad too, and the bed heats up slowly enough that I doubt that it can reach a temperature high enough to be a fire risk - but I haven't actually tested this.
But I repeat, it is extremely unusual for a bed heater mosfet to fail unless there is a short circuit across the bed heater. In printers with moving beds, there is always the risk of the bed heater wires chafing unless suitable precautions are taken.
Duet WiFi hardware designer and firmware engineer
Please do not ask me for Duet support via PM or email, use the forum
http://www.escher3d.com, https://miscsolutions.wordpress.com -
@dc42
I will examine the bed wires to see if that is the case. -
@dc42
I submitted a tech support request to M3D but have not seen any response yet. Frankly, I am not confident that M3D will warranty this board.Is it possible to use an external Mosfet or SSR with the Maestro? Perhaps by connecting to the E1 heater header and re-configuring the firmware? Or by connecting to the Expansion header?
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On further investigation it is fairly obvious that the wires shorted against the aluminum bed. Looking at the way this connection was set up by the manufacturer, this short seems like it was inevitable.
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yikes
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TronXY X5S with Duet 3 MB6HC and Roto toolboard : Cartesian bed-slinger with Duet 3 Mini 5+ WiFi and 1LC : RRP Fisher Delta v1 with Duet 2 Maestro : Polargraph with Duet 2 WiFi
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@droftarts said in Duet Maestro Bed heating uncontrolled:
@NTX9 Yikes indeed! Best check yours, @dc42 !
Ian
I will!
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For what it is worth, I have two and the newer one is in better shape.
Is the chip next to the LED on the board, the Mosfet that has been damaged? Or is there a diagram that shows the layout of the board.
The leads on that appear substantial enough that I might brave replacing the chip.
M3d customer service is slow at best and I don't have much faith that they will warranty the board.
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@NTX9 said in Duet Maestro Bed heating uncontrolled:
Is the chip next to the LED on the board, the Mosfet that has been damaged?
Yes, the one marked 036N04L. To replace it you will need a hotplate as well as hot air, because of the amount of heatsinking that the PCB provides.
My Quad is in better shape than your photo, but there is some bare wire very close to the edge of the aluminium. I'm going to put some Kapton tape in the gap and over the edge of the aluminum.
Duet WiFi hardware designer and firmware engineer
Please do not ask me for Duet support via PM or email, use the forum
http://www.escher3d.com, https://miscsolutions.wordpress.com -
@dc42 @NTX9 Those bare wires on the heatbed do look crazily close to the edge. Could you desolder them and resolder the other way around, so they looped back, with insulation over the edge of the bed? Or would you need to heat the bed to 200C first, as it's a massive heatsink?
Ian
TronXY X5S with Duet 3 MB6HC and Roto toolboard : Cartesian bed-slinger with Duet 3 Mini 5+ WiFi and 1LC : RRP Fisher Delta v1 with Duet 2 Maestro : Polargraph with Duet 2 WiFi
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@droftarts
Ian, That is exactly what I plan to do. I may also add some kind of printed cover if I can find or design something that seems suitable. I am not sure how difficult re soldering will be but the alternative is to replace the bed. -
@dc42 said in Duet Maestro Bed heating uncontrolled:
Yes, the one marked 036N04L. To replace it you will need a hotplate as well as hot air, because of the amount of heatsinking that the PCB provides.
Yikes, that sounds like a golden opportunity to totally bogger up the board.
Maybe I will go with an external mosfet afterall.
Are there pins on the expansion board that would bypass the onboard mosfet? Or would I need to attach to the gate pin on the onboard mosfet?
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While this issue is clearly the result of a short at the heated bed, it would seem like the Duet board would have a fuse to protect against this kind of fault.
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@NTX9 said in Duet Maestro Bed heating uncontrolled:
While this issue is clearly the result of a short at the heated bed, it would seem like the Duet board would have a fuse to protect against this kind of fault.
Sadly, fuses are usually too slow to protect mosfets. OTOH, in many cases the short-circuit protection of the PSU does provide sufficient protection - but evidently not in this case.
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Unfortunately fuses aren't fool proof; if you're looking for a warranty claim I'd look to the printer manufacturer instead.
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@dc42 said in Duet Maestro Bed heating uncontrolled:
@NTX9 said in Duet Maestro Bed heating uncontrolled:
While this issue is clearly the result of a short at the heated bed, it would seem like the Duet board would have a fuse to protect against this kind of fault.
Sadly, fuses are usually too slow to protect mosfets. OTOH, in many cases the short-circuit protection of the PSU does provide sufficient protection - but evidently not in this case.
Even if the fuse doesn't prevent damage to the mosfet, I would hope that it would at least prevent the bed from heating uncontrolled.
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@bearer
Unfortunately, it appears that M3D has no interest in covering this under warranty. -
@NTX9 said in Duet Maestro Bed heating uncontrolled:
Even if the fuse doesn't prevent damage to the mosfet, I would hope that it would at least prevent the bed from heating uncontrolled.
Maybe, if the short circuit lasts long enough to blow the fuse. But bed heaters should always be protected against uncontrolled heating anyway, either passively (by ensuring that the maximum temperature reached is safe), or actively (using a thermal cutout).
Duet WiFi hardware designer and firmware engineer
Please do not ask me for Duet support via PM or email, use the forum
http://www.escher3d.com, https://miscsolutions.wordpress.com -
@NTX9 said in Duet Maestro Bed heating uncontrolled:
Even if the fuse doesn't prevent damage to the mosfet, I would hope that it would at least prevent the bed from heating uncontrolled.
That would have the side effect of slowing down the bed heating as well; normally the bed is on more or less 100% until it starts getting close to the set point and the power level tapers off to settle on the chosen temperature. The (electrical) fuse can't distinguish between desired and undesired heating.
A thermal fuse would be the appropriate safety device to prevent over heating in such a case, which would be part of the bed, not the controller.
It doesn't make sense to cripple a controller board because someone makes a printer that literally sh¤# the bed.
As far as the manufacturer not seeing it as a warranty claim that would be nothing but bad publicity if the product is still in its warranty period - there is no doubt the fault is poor design or manufacturing; ultimately if the warranty has expired it doesn't matter.
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What is considered a safe maximum temperature for a 3D Pinter bed?
It seems to me that is dependent as much on the furnishings of the space around the printer as the machine itself. For example wood paneling that is common in basements or wood furniture can have spontaneous combustion at prolonged temps as low as 110c.
