Monday, August 22, 2011

"Death to the Resistors!" update A

So here's the story so far,
I've got five resistors, nominally valued at 100 ohms.  I'm going to execute a plan to test their power rating.  I've learned a lot about testing standards, and resistor power ratings, probably more than I wanted to know.  Apparently there are some rigid standards, and exacting practices people go through to test and certify parts for particular applications.  Some of these tests are daunting to say the least!
Test a resistor for 10000 hours?
Meh, not going to happen for me.
That's just one of the current requirements a manufacturer has to meet for the current round of MIL-SPEC testing.
I'm not going to MIL-SPEC certify these resistors.  I am however, going to take some suggestions offered to me from the good folks on QRP-L.
From Mike WA8BXN:

Sounds like you want to do some destructive testing. How will you relate that to what should be their normal power rating?

Rather than doing a destructive test, it might be interesting to find the power that takes the resistor above its rated temperature.

Another test that would be interesting is to measure resistance after cycling power on and off. This is related to checking the next day but is different because I would run through more powered cycles.

What ever tests are done should also be done with resistors of known good quality and specifications.
Good suggestions!
I'll devise a series of tests, first thing I have to do though is rig up a test jig to measure the actual value of the resistors!  My first attempt was a bust due to 9v battery issues on my digital VOM.  Once I took care of that, I realized it can be pretty tricky to measure the values of the resistors.  They have this thing about holding still.  I don't think they like going into the holes that I stuff them in.  I'm pretty sure the hot tin/silver amalgam I apply to them upsets them too.
I've only ever had one capacitor blow up on me though... long story, but I now never apply power to a rig with the top off without first putting on my safety glasses, and yes, I had safety glasses on that time!


Peter Enmore said...

What type of resistors are you using for this test?

GB Hoyt said...

El Cheapo Ebay resistors nominally rated at 1/4 watt.