blowing resistor
blowing resistor
(OP)
A slightly unusual one.........
We have some 1 meg 0.2W smd resistors that are encased in potting compound and need to blow them open circuit down the wires from the outside.
Equipment we have available includes a 0-450V Varic and a 0-5kV 5mA flash tester.
As most of my previous contact with resistors has involved trying to not blow them up I'd appreciate any input.
We have some 1 meg 0.2W smd resistors that are encased in potting compound and need to blow them open circuit down the wires from the outside.
Equipment we have available includes a 0-450V Varic and a 0-5kV 5mA flash tester.
As most of my previous contact with resistors has involved trying to not blow them up I'd appreciate any input.





RE: blowing resistor
Would it work to blow open one wire instead of the resistor? A 200 mW SMD resistor will probably fail temporarily shorted if you put high voltage across it. Put a capacitor parallel to your flash tester to get a nice heavy current pulse to blow the wire clean. You will probably not need all the 5 kV, so capacitor choice is somewhat easier.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: blowing resistor
No other circuitry, two wires go into the potting compound, each is soldered to a piece of copper mesh, the resistor is soldered between the two bits of mesh.
They want to blow the resistor but keep the connections to the mesh
RE: blowing resistor
The square root of 2Meg is 1414 so that's the voltage needed to get 2 watts of power in that resistor. While it won't be "blown apart" by that wattage, I would expect it to burn open in 10 seconds or so. More voltage would make it happen faster but eventually you will get some "collateral damage" which you don't seem to want.
Good luck. This even sounds like a bit of fun. Let us know how it works out.
RE: blowing resistor
5kV and 5 ma = 25 Watts.
That should do it.
Try one and let us know how much collateral damage you suffer. grin
Bill
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"Why not the best?"
Jimmy Carter
RE: blowing resistor
I did think of a capacitor but the flash tester trips at 5mA so I didn't think I'd be able to charge it up without lot of messing about with series resistors
We have a couple of samples to practice on before the real thing which is lucky as if I can't pop them my client ends up spending a week digging all the potting out and redoing it
RE: blowing resistor
Not sure if one can guarantee a flash over across the resistor, but that is the most likely outcome. When that happens, no thermal effects from a 5 mA power supply can do any damage because the voltage goes to zero. Or almost.
That is why you should use a capacitor to get enough punch to blow either the resistor or the wire away. If you don't want to hurt the wire, a drill is probably the safest way to go. I would chose that in any case.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: blowing resistor
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: blowing resistor