[aprssig] Amazing resistors

Robert Bruninga bruninga at usna.edu
Fri Sep 5 19:10:16 CDT 2014


We have been running a 0.25 Watt small resistor at 3.5 Watts ALL DAY and
it still wont burn out!

We were using it as a "burn resistor" to release a fishing line mechanism.
It does that in 2 seconds.  But now 10 hours later it is still going and
wont burn out!  (We had hoped it would eventually open so that we could
use the same control line for something else after the resistor opened up.
But it wont.

This is amazing to me.  We know that an old composition resistor will burn
smoke and crack in only a few seconds at these power levels, but not the
carbon film at 14 times overload!

Here is the scenario:  7.5v across a 15 ohm  0.25W carbon film resistor.
. It burns the fishing line in 2 seconds
. It begins to smoke at 5
. It smokes for a minute or so
. Then, is black, but no further visible changes
. After an hour it has changed resistance to 20 ohms
. After 5 hours it is up to 29 ohms
. After 10 hours it is up to 35 ohms
. Of course the V^2/R power is going down, but it wont burn out!

Just thought you might find this data point useful!

Bob, WB4APR


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