recent issue heating bed..funny smell
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Hello everyone, I don't know what's going on with my printer. I will try to explain in detail what is happening. Currently when I try to turn on my heated bed. it will start to smell. I've looked at my grounds going into Vin and one for the bed. I also have a duex5 which I checked the wires on also. All look ok and are snug, I pulled them all to inspect the wires and re-crimped one in a new ferrule. The smell is not of burning plastic, at least not to my thoughts but rather like very hot electronics. I even purchased a replacement duet wifi thinking the board might have been the issue but that was not it as I still smell the same smell as soon as I turn on the heated bed. was trying to reach a bed temp of 80. So nothing too crazy. I also noticed on the new duet board, the fuse was getting really hot for the bed. I could use some help to further diag this thing. I need to get my printer back up and running to complete a job for someone.
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@gnatman how big is your bed? what voltage are you running at?
do you know how many watts it needs? -
@jay_s_uk said in recent issue heating bed..funny smell:
@gnatman how big is your bed? what voltage are you running at?
do you know how many watts it needs?It's 16" x 16" 24v system. I am running a Hypercube evo. bought the kit from alliexpress like 3 or 4 years ago. I can't remember the wattage of the bed.
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@gnatman said in recent issue heating bed..funny smell:
16" x 16"
looking online thats going to be about 500w.
This would equate to 21amps so you're above the recommended rating for the bed mosfet (18amps).
Best to move to an external mosfetOwns various duet boards and is the main wiki maintainer for the Teamgloomy LPC/STM32 port of RRF. Assume I'm running whatever the latest beta/stable build is
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@gnatman The bed plate acts as a heatsink for the heater. If the heater detaches from the plate or develops an air bubble between the heater and plate, the heater won't be able to transfer heat to the plate and the heater will get extra hot in that area. I'd inspect the bed and heater carefully to see if there are any areas that have let go.
I had this happen after about 2 years operation:
The acrylic adhesive on the heater dried up and let go of the plate. The silicone/glass heater scorched in the area where it detached from the bed plate. The outside surface of the heater looked fine- only the inside surface was burned, but the air bubble was obvious. I never noticed a smell, but the printer is usually closed when it's operating.
When I replaced that heater I ordered the new one without adhesive and used high temperature silicone to attach it to the plate. It's been about 2 years now and there are no signs of the silicone letting go.
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Photos of the bed heater?
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@jay_s_uk said in recent issue heating bed..funny smell:
@gnatman said in recent issue heating bed..funny smell:
16" x 16"
looking online thats going to be about 500w.
This would equate to 21amps so you're above the recommended rating for the bed mosfet (18amps).
Best to move to an external mosfetI've been printing this way for like 3 years or more. I don't think that is the issue.
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@mrehorstdmd said in recent issue heating bed..funny smell:
@gnatman The bed plate acts as a heatsink for the heater. If the heater detaches from the plate or develops an air bubble between the heater and plate, the heater won't be able to transfer heat to the plate and the heater will get extra hot in that area. I'd inspect the bed and heater carefully to see if there are any areas that have let go.
I had this happen after about 2 years operation:
The acrylic adhesive on the heater dried up and let go of the plate. The silicone/glass heater scorched in the area where it detached from the bed plate. The outside surface of the heater looked fine- only the inside surface was burned, but the air bubble was obvious. I never noticed a smell, but the printer is usually closed when it's operating.
When I replaced that heater I ordered the new one without adhesive and used high temperature silicone to attach it to the plate. It's been about 2 years now and there are no signs of the silicone letting go.
Here is the underside of the bed, looks fine to me. not even a short on the thermistor. I checked the power and neg on the bottom of the bed and re-soldered the neg wire just to be safe.
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@phaedrux said in recent issue heating bed..funny smell:
Photos of the bed heater?
plug, wires or both. attached is an image of the bottom of the duet. keep in mind I soldered the terminals on the bottom because it "felt" loose so there is a little mess from that. rosin core solder.
along with the terminal in the other photo. you can see VIN looks like it might have been getting some heat. but no melted plastic. also I only smell it when the bed is heating up. No smell on idle nor when the hot end is heating up. last image is of my PSU.
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Did you tighten down those screw terminals every now and then?
They can loosen slightly to the point where the increased resistance of the connection can start to create some serious heat.
That may have happened to you.
Frederick
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@fcwilt said in recent issue heating bed..funny smell:
Did you tighten down those screw terminals every now and then?
They can loosen slightly to the point where the increased resistance of the connection can start to create some serious heat.
That may have happened to you.
Frederick
I have, I also installed a replacement board which did the exact same thing. I have a Duet wifi 1.02 and now a replacement wifi which has the blade style fuse between the two terminals. This one also would smell on bed heating and also I mentioned the blade fuse getting pretty hot. (new to me as my old board doesn't have the blade fuse there)
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I swapped out all power wires, and so far it seems to be ok. not sure if there was still some issues going on with the ground wire that has the duex5 ground or whatever but I think all is good.
I will keep checking the wire to make sure it's still going strong and not too much current on the wire. I swapped the 12g that was the pos/neg from the vin to 14g. that same 14g is on the duex5 too.
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You are exceeding the current capacity of the Duet. Go to an external relay or mosfet!
Yes I realize you might 'just' be inside the limits (didn't bother to verify) but you are no longer in a comfortable operating range. -
@gnatman said in recent issue heating bed..funny smell:
@jay_s_uk said in recent issue heating bed..funny smell:
@gnatman said in recent issue heating bed..funny smell:
16" x 16"
looking online thats going to be about 500w.
This would equate to 21amps so you're above the recommended rating for the bed mosfet (18amps).
Best to move to an external mosfetI've been printing this way for like 3 years or more. I don't think that is the issue.
Says the man who's printer smells like burning.
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@gnatman something to bear in mind is that the power draw will always be higher when the bed is heating up. It will be on full cycle while heating, whereas when maintaining temperature it will PWM control so only part duty.
Also with many resistor heaters, the resistance tends to increase a bit as they heat up, so the power draw decreases when they're at temperature.Sounds like your issue might have been in your wiring (could be some broken strands or poor contacts in your crimps?), and the fuse getting hot is probably from too high a current draw.
If you dont want to run an external mosfet (I would and do on mine!), you could at least adjust your PSU output down a bit to reduce the power. It's definitely worth thinking what will happen if/when the Duet mosfet eventually blows and fails closed
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@jens55 said in recent issue heating bed..funny smell:
You are exceeding the current capacity of the Duet. Go to an external relay or mosfet!
Yes I realize you might 'just' be inside the limits (didn't bother to verify) but you are no longer in a comfortable operating range.I'll look at adding a mosfet, do you have one you would recommend. I'm 95% sure it was just one of the neg cables screws being loose on the terminal. I didn't replace all the ends or wires the first time, I just did one side of one neg wire. then swapped the board. This time I did all of the wires.
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@phaedrux said in recent issue heating bed..funny smell:
@gnatman said in recent issue heating bed..funny smell:
@jay_s_uk said in recent issue heating bed..funny smell:
@gnatman said in recent issue heating bed..funny smell:
16" x 16"
looking online thats going to be about 500w.
This would equate to 21amps so you're above the recommended rating for the bed mosfet (18amps).
Best to move to an external mosfetI've been printing this way for like 3 years or more. I don't think that is the issue.
Says the man who's printer smells like burning.
I think it was just a cable being loose. I was able to resolve it once I replaced all the wires
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@gnatman said in recent issue heating bed..funny smell:
@jens55 said in recent issue heating bed..funny smell:
You are exceeding the current capacity of the Duet. Go to an external relay or mosfet!
Yes I realize you might 'just' be inside the limits (didn't bother to verify) but you are no longer in a comfortable operating range.I'll look at adding a mosfet, do you have one you would recommend.
Sorry, I am the wrong person to ask - I run a China SSR that is almost certainly a clone even though I know better
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after going strong for a day, it started to smell again, this time I was not home but my wife was and she stopped the printer. I purchased this mosfet https://www.amazon.com/dp/B08YZ4W4LN?psc=1&ref=ppx_yo2_dt_b_product_details
Based on the image, how do I hook this up. My heated bed has a pos/neg wire plus wires for the thermistor. I don't want to be wrong here but are the blue wires in the image supposed to be the thermistor wires or are they trying to show there is no polarity on the wires coming off the bed going to the mosfet. Im just confused slightly by the blue wires in the diagram.
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@gnatman there's no polarity coming off the MOSFET. It's just a big resistor and the cables can be used either way
