Heated Bed Safety Issues

Hi everyone,
We are looking into putting together a 12" x 12" heated bed for our new printer and are probably going to go with a nichrome wire heated version. We are concerned about safety issues with heated beds. With our setup (size and want to be able to print ABS and hopefully nylon) we will need three or four nichrome wire lengths or "elements" -we want to integrate thermal cutoff,s something like this one from Digikey: thermal cutoff Has anyone used this sort of cutoff or some kind of fuse/breaker system for heated bed purposes? We want a fail-safe system in case the thermistor fails or some other unforeseen incident causes the heated bed to overheat. Does anyone have any ideas of how heated beds in general could be fail-safed? The heated bed seem to be one of the most potentially dangerous components of the printer.

Thanks for any ideas and comments,

Jacqueline

Our 3D Printer Blog

Yes I use resettable thermal fuses on my heated beds that use resistors. The PCB ones are self limiting because the resistance increases with temperature.

The other issue is the wiring has to be flexible and have a minimum bend radius enforced if the bed moves. If not it fractures one strand at a time until the wire starts burning.

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Thanks for the input!

I had a look around for the "resettable thermal fuses" that you mention and can't seem to find anything like that -what I keep finding seems to be more concerned with current and not temperature. Maybe I am just looking in the wrong places. Would you happen to have a link/part number for the type that you are using? The resettable aspect might be more practical than the ones that I was looking into that just break and have to be replaced if something gets too toasty!

The wiring issue is important for us as well -the bed for our machine will be the back and forth (Y axis) moving type.


Jacqueline

Our 3D Printer Blog

Search for "thermostat", or contact thermostat or surface thermostat, something like this one. Its the old principle of bimetalic component which swings one side or the other because each metal has different thermal dilatation coeficient. It has a temperature from which it closes and one at which it opens the circuit. Depending on their order these can be normally open (NO) or normally closed (NC) - you probably want the NC, and it will open (disconnect) at its opening temperature, which should be the max temperature +some hefty margin (coz its a safety measure, not to be triggered everyday).

Edited 1 time(s). Last edit at 08/28/2013 08:41PM by NoobMan.

Thanks for the information - I will have a look into these. We were thinking the same thing about the max temperature for the cutoff, that it should be the desired heated bed temperature (for example 150C) plus 20 - 40 degrees -as you say, it is a safety measure and we sure hope it won't be triggered every day!

Jacqueline

Our 3D Printer Blog