Heated bed started smoking January 17, 2019 03:09PM |
Registered: 5 years ago Posts: 29 |
Re: Heated bed started smoking January 17, 2019 04:40PM |
Registered: 9 years ago Posts: 465 |
Re: Heated bed started smoking January 17, 2019 04:48PM |
Registered: 9 years ago Posts: 978 |
Re: Heated bed started smoking January 18, 2019 02:57AM |
Registered: 6 years ago Posts: 1,007 |
Re: Heated bed started smoking January 18, 2019 02:03PM |
Registered: 5 years ago Posts: 29 |
Quote
SupraGuy
1.3 Ohms is reasonable for a 12V heated bed, that would be about 110W, drawing about 9A of current.
A thermistor shorted to ground can do some weird things Shorted to power could do some other things, some of them very bad, like destroy your control board. Protecting from short circuits is a good thing, people should do that.
Re: Heated bed started smoking January 18, 2019 02:06PM |
Registered: 5 years ago Posts: 29 |
Quote
frankvdh
I wouldn't expect that the thermistor contacting the heat bed would cause a short bad enough to cause smoke, except that you might get bad temperature readings from the bed, which might cause your controller to overheat the bed eventually.
Even if some other wire was contacting the bed, the thermistor wires are so fine that even if they did burn out, you probably wouldn't even notice the smoke.
So I'm thinking the problem is elsewhere; power wires touching the bed perhaps.
Try disconnecting the bed heater wires from the supply and turn on the printer. Does it show a valid bed temperature?
Is this a 12V or 24V or mains-powered heat bed?
Re: Heated bed started smoking January 18, 2019 02:17PM |
Registered: 5 years ago Posts: 29 |
Quote
MKSA
The hot spot (partially burnt track) is very close to the +12 soldering pad. In case of a short (whisker of solder ..) the +12 V touching this track, it would create this and may even burn away.
The measured value for the heating track is OK. So most probably fine.
The Al plate is isolated from the heating tracks. Did you connect to 0V/GND.
Can you show how the thermistor is installed ?
Re: Heated bed started smoking January 19, 2019 03:35AM |
Registered: 6 years ago Posts: 1,007 |
Quote
chrstrvs
Quote
MKSA
The hot spot (partially burnt track) is very close to the +12 soldering pad. In case of a short (whisker of solder ..) the +12 V touching this track, it would create this and may even burn away.
The measured value for the heating track is OK. So most probably fine.
The Al plate is isolated from the heating tracks. Did you connect to 0V/GND.
Can you show how the thermistor is installed ?
Do you mean if the aluminium plate is grounded? If so, it is not. Should it be?
I forgot to take a picture, but it's installed like any other thermistor is installed in these heat beds. Like this.
I looked at everything today and couldn't find a reason for the smoke/short, so I put a 15 amp fuse on the between the bed and the Ramps board and started heating the bed. After a few minutes of it being stable at 60°C I started printing. After a few minutes the fuse blew and the printer halted due to "Thermal runaway".
I don't understand why the bed works fine for a while and then blows the fuse. Any ideas?
Oh, and thank you all for your help so far!
Re: Heated bed started smoking January 19, 2019 07:13AM |
Registered: 5 years ago Posts: 29 |
Quote
MKSA
Quote
chrstrvs
Quote
MKSA
The hot spot (partially burnt track) is very close to the +12 soldering pad. In case of a short (whisker of solder ..) the +12 V touching this track, it would create this and may even burn away.
The measured value for the heating track is OK. So most probably fine.
The Al plate is isolated from the heating tracks. Did you connect to 0V/GND.
Can you show how the thermistor is installed ?
Do you mean if the aluminium plate is grounded? If so, it is not. Should it be?
I forgot to take a picture, but it's installed like any other thermistor is installed in these heat beds. Like this.
I looked at everything today and couldn't find a reason for the smoke/short, so I put a 15 amp fuse on the between the bed and the Ramps board and started heating the bed. After a few minutes of it being stable at 60°C I started printing. After a few minutes the fuse blew and the printer halted due to "Thermal runaway".
I don't understand why the bed works fine for a while and then blows the fuse. Any ideas?
Oh, and thank you all for your help so far!
Normally all metallic parts should be grounded but it has nothing to do with your issue.
It looks like may be due to thermal expansion, the heating track of the bed gets shorted. The thermistor and wiring looks OK as it worked and detected the thermal runaway.
Disconnect the bed from the controller board, power it directly from the 12V (I suppose it is 12V as the bed is wired for 12V) via a switch, the 15A fuse and an ammeter if you have one.
If you don't have a thermometer use the printer controller as a T° probe for the bedr.
Turn ON the bed switch and look at the T°, turn off if the T° reaches 100°. If the fuse blows or smoke before, the bed is defective. Look closely where it is burnt, watch if nothing could short the 12V solder pad to the track, or at the bed mounting screws.
Note, it is an easy problem, provided one has the machine on hand.