As I had predicted, we were now using the item way outside of it's specification, and that's it's life expectancy was certainly going to be, erm, compromised....
Well, tonight it happened. It stopped getting warm. Now I've got a commercial prototype to get out, and I need it. Let's see what's happened.....
So, the poor thing is once again disassembled. Those two red wires you can see running from the other side of the PCB are connected to the element.... A quick check with the meter, and ... it's open circuit. Damn.
Now, in the last modification I decided to raise the temperature by modifying the controller. So what if there's one of those non-resetable thermal fuse things on the element somewhere....
And there is! Mounted against the lower heating element...
It's duly removed, the two wires soldered together, and insulated with a piece of heatshrink...
Back in business!
Now, we've removed an essential safety device, so I'll re-iterate my previous warning... We're putting paper in here, which is being exposed to higher temperatures for more time than it would be in normal use.... If it should jam, there's a risk it could smoulder and catch fire, and ruin your day... DON'T USE IT UNATTENDED!
... you nkow what , I may just build a combined speed/ temperature controller for it, and have done ...
As it is a safety component, and since your blog is public, it might be useful for others to know (as I am sure that you do already) that thermal fuse replacements are available from CPC, Farnell and Rapid with ratings up to 240 degC.
ReplyDeleteA good plan, and whilst this unit is being operated well in excess of original design remit, it would be an excellent idea to refit a better rated fuse, if only to prevent fire in the event of failure of the sensing diode. It is imperative not to operate the unit unattended, however.
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