Burnin’ down the house.
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Running duet with this mosfet connected to bed.
Bed temp 55c
Hot end running at 220cSmelling burnt plastic, look down and see the mosfet pla cover melting.
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Did you give the heat sink any airflow?
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@gavatron3000 Just the vents that you see.
Been running it like this, for some reason it got really hot this time.
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Yikes.
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Got any specs of your hardware? How much current you are passing? On resistance of the MOSFET? It'll be a good case study.
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That doesn't look like proper airflow to me. I suppose the widening gaps prevented it from catching fire. My suggestion is to make a force-ventilated case that encompasses all the components as opposed to covering them one by one.
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I had an identical looking Mosfet almost catch fire about a year ago. Had proper airflow over the top of it. Buying cheap random brand parts from Amazon usually works out great, but sometimes you get a dud.
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always-on fan on top?
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next enclosure out of PolyCarbonat (choose black for UV-protection) (is flame reluctant (not unflammable, but at least it takes longer))?
?
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@lb Found out why it overheated. On the mainboard where you screw in the bed heater wires, they were little exposed and touching. so it arced and started heating up. Make sure when you screw your wires into board that no metal wire is exposed and that its covered so they don't touch or arc.
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@chriskimbr That's what the ferrules are for.
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But even with ferrules you need a good light if you do that in the night, because in a dim lit room it happened to me that even with ferrule-crimping I missed one of those wires thin like a hair...
but yeah it is always good to do the complicated things in the morning with the sun shining I guessWill check on saturady my wiring again after seeing your picture
good luck & thanks for sharing! -
I recently bought some fire retardant ABS, from here:
http://www.sovb3d.fr/abs-175mm-ignifuge-1kg/52-fil-abs-blanc-ignifuge-175mm-1kg.html
I ran a test, and it indeed does not propagate fire.
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You want to use low ON resistance mosfet to reduce the generated heat. For example, like this one
https://www.auberins.com/index.php?main_page=product_info&cPath=2_30&products_id=288
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Did you need more than 15A of current, and if so, why?
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@jrdm perhaps because they are following recommended heating capacities and for cost reasons are sticking to 12V.
Folowing the Duet docs gives over 15A for a 220mm square bed. Plenty of beds bigger than this about too. Large enough to give the 18A current limit of the Duet 2s a threat.
https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater
Where has 15A come from?
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@doctrucker said in Burnin’ down the house.:
@jrdm perhaps because they are following recommended heating capacities and for cost reasons are sticking to 12V.
OK I thought most DC beds had switched to allowing two different voltages.
Where has 15A come from?
According to the Duet wiki, that's the rating of the fuse provided for protecting bed circuit. At first glance, 18A ATO fuses aren't readily available.
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@jrdm fair point!
The docs I linked specified 18A, but I think not all the Duet 2s had fuses and it's the fuse holder that limits ot to 15A.
