[amsat-bb] Antenna Burn Resistor data

Gary Mayfield kk0sd at tnics.com
Sun Sep 7 03:20:35 UTC 2014


	Are you testing in a vacuum? I suspect without the air to cool the resistor it may be more likely to burn out.

Just a Thought,

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Robert Bruninga
Sent: Friday, September 05, 2014 7:14 PM
To: amsat-bb at amsat.org
Subject: [amsat-bb] Antenna Burn Resistor data

While testing a Burn resistor to release an antenna on our cubesat, we are
AMAZED at the result.

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

We use it as a “burn resistor” to release a fishing line antenna release
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 or smoke

• 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!

We had known that they were quite resusable numerous times when used for 5
seconds or so at a time.  But never expected 10 hours and still going!

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