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Resistor for neon indicator lamp

Thanks John, I must admit it's hard to understand how a 3 watt 100k ohm resistor across the 240 V lines would blow even if everything down stream of it was shorted. (As your calculation shows.) A new circuit board is in the mail, but this won't solve the mystery. The board has been redesigned and is no longer analog but digital. Once I put the new board in I'll look at the busted one and see if I can figure anything out.

Say could you resend that link to the neon bulb I-V curve? What ever you posted got turned into gobble-de-gook by google.

" snipped-for-privacy@4ax.com"

George H.

Reply to
George Herold
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Jon

Reply to
Jon Kirwan

In , George Herold wrote in part:

I have seen resistors fail in ways that cause their resistance to decrease until they get toasted and then go open circuit.

My experience has been that this happens more with carbon composition resistors. Those tend to be cylinders with untapered ends. Many times, the composition is exposed. The composition may absorb moisture and experience a decrease in resistance, especially if it is operated only intermittently. This is more likely to be a problem where there is exposure to moisture or high humidity or salty coastal air.

And carbon's resistivity has a negative temperature coefficient.

Preferably the resistor degrades rapidly and then goes open circuit quickly by the time it allows anything else to get overloaded to a damaging extent.

A possible other explanation is that a severe line voltage surge caused something in the resistor to carbonize. The resistor becomes more conductive and hotter. The carbonization may then go into a runaway situation, leading to sizzle-sizzle and then to *pow*, *poof* or *phut*.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein 

--
Ah, Google...

Google groups doesn't support binaries so I'll email it to you.

JF
Reply to
John Fields

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Thanks Don, This certianly wasn't a carbon composition. (Though I was digging through a pile of 1-2 Watt 100-300k ohm carbon C's at work today.) It doesn't seem like putting 100k in there can hurt anything, though I don't expect it to work either... I figure something else might have happened also.

George H.

Reply to
George Herold

Wow. Thanks John

Reply to
George Herold

Not sure if my email got to you, George. So just verifying by the usual post-a-message-on-the-public-cork-board method, sometimes called a newsgroup.

Let me know.

Jon

Reply to
Jon Kirwan 

--
You're welcome. :-)

If you're interested in neon glow lamps, GE's 1965 glow lamp manual
(pretty much the Bible) is here:

http://www.donsbulbs.com/cgi-bin/r/t.pl/library.html

JF
Reply to
John Fields

n

Excellent, lots of reading there!

George H.

Reply to
George Herold

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