EEVblog Electronics Community Forum

EEVblog => EEVblog Specific => Topic started by: adam_lumpkins on August 01, 2011, 04:43:05 pm

Title: eevblog#191
Post by: adam_lumpkins on August 01, 2011, 04:43:05 pm
There are so many ways this could be done.  I like daves way,  but, I did some work with graphite It works great as an ignter..... there are many different sizes. I had some luck useing them as resistors. 
Title: Re: eevblog#191
Post by: NiHaoMike on August 02, 2011, 03:08:42 am
That could be useful for making a very cheap one shot relay. The thermal inertia would be particularly useful if you don't want an instant trigger. Or hot glue a piece of string to a chip or other part on your board and it would go off if something goes wrong and it overheats. At work, someone had problems with a part shorting out internally and burning the traces off an expensive board. The quick fix is a piece of string hot glued to the chip on one end and tied to a microswitch on the other. If the part gets hot enough to melt the glue, the switch springs back and cuts power. (They soon got a power supply with a programmable "protective relay" that can be set to trip only on certain voltage/current profiles as well as overtemperature. Ironically, the first one they got failed to trip and burned the board anyways...)

Actually, prior to the common availability of cheap high power semiconductors, I remember about a science fair project someone did that used a mousetrap (as a cheap high current switch) and some disposable camera capacitors to launch a steel marble. (I forgot if it was a railgun or coilgun.)
Title: Re: eevblog#191
Post by: ejeffrey on August 02, 2011, 10:25:57 am
Quote
At work, someone had problems with a part shorting out internally and burning the traces off an expensive board. The quick fix is a piece of string hot glued to the chip on one end and tied to a microswitch on the other.

I am all for clever hacks, but.. how about a fuse?  Or a polyswitch?
Title: Re: eevblog#191
Post by: NiHaoMike on August 03, 2011, 01:01:55 am
The device in question often draws a lot of current (sending it to an external load) in normal operation. The problem happens when the device internally dissipates a lot of power. Therefore, the solution is a device that disconnects power before it gets hot enough to damage the board. The hot glue did that, as does the remote thermal cutout feature of the new power supply.