Xmas tree incandesent's die as

Xmas tree incandesent's die as dead shorts.

How da do dat? OK I'm feeling lazy and not searc...

George H.

Springy filament supports that short to another contact when the filament melts/vaporizes.

Cheers! Rich

Oh, the filament holds the (springie) support back, and when it burns out the support makes contact on the other side?

George H.

That's the way I understand it, yes. Maybe sacrifice one, carefully break the envelope, and look and see?

Good Luck! Rich

Thats to keep the others burning. Until the higher voltages on the rest kill the whole chain.... High voltage kills something in the foot of the broken light, causing a short.

Many incandescents made for use in series strings are designed to become shorts upon being presented with full line voltage as a result of failing open. The explanation that I usually hear is add-on parts that short upon receiving full line voltage.

On the other hand, 120V incandescents used for Christmas (generally C7 and C9) fail open and stay open. If they become shorts instead, then burnouts would pop breakers or pop something.

--
 - Don Klipstein (don@misty.com)

C7s and C9s are usually parallel strung (w/ 120V bulbs). It's the minis that are series strung and recent ones have the short-in-the-base thing.

looking through the glass envelope I see what appears to be a bunch of wire wrapped around the filament supports, I guess it has a coating that will burn through when it's hit by the fault voltage and become conductive.

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?? 100% natural

A pair of anti-parallel Zeners would be better.

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What are you looking for, all the way down here?

I found a picture here,

Thanks. George H.

1V Zeners are really lousy.

On the other hand, forward-biased LEDs have a pretty sharp knee. Hey, then after the incandescent blew out, the LEDs would carry on forever! Or until enough of the other incandescents blew to prevent current limiting...

Best regards,

Bob Masta DAQARTA v6.00 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, FREE Signal Generator Pitch Track, Pitch-to-MIDI Science with your sound card!

that

They don't have to be that low. If they were, they would all be so soft that the leakage current would be higher than the lamp current. Anyway, I don't recall a 120 lamp string with 1 V lbulbs. The 100 lamp I've seen had two strings of 50, with a three wire cord. That means the bulbs are 2.4 volts, so a working lamp has 1.2 *1.414 or 3.3936 volts peak across a lit bulb. Five volt Zeners would be fine, ssince you don't want them to conduct, except under failure mode.

Some people who restore old series string tube radios use a pair of 9 volt across the pilot lamps which are powered off a tap in the filament in the 35 V rectifier. You can lose the tube, when the pilot lamp burns out but the pair of diodes will protect it. It was my idea, and I had to argue with them for a while before it sank in. They kept insisting that you needed 6.3 volt Zeners acrross a 6.3 volt pilot lamp. Of course, these are the same people who insisted that putting a diode in series with a string of filaments cut the effective voltage in half.

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that

Want to try that again? After too many lamps fail, the forward voltage would be too hight to light your LEDs.

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that

Nonsense.

Perhaps you're wasting money on the incandescent lamp?

that

Power dissipation?

Klipste> >> >>

that

Geeze! It's kind of pointless now, but before LED strings were availible it would have been worth the time & effort to manufacture series strings with the diodes to make it easy to find the bad lamps. The entire string is just a few watts. Did you know that there are plug in LED replacements for the mini incandescent lamps?

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Klipste> >> >>>

of

C7

minis that

It would have been funny if it was possible. The idea for the zeners was something from long before they sold LED strings.

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Klipste>> >>>

that

Hey, it was a joke, after all! The idea was that the incandescents are the current limiting resistors for the LEDs, so if all the incandescents failed there would be no current limiting. Assuming red LEDs at 1.4V each, that would let the magic smoke out. But of course, why would anyone bother with incandescents if they had LEDs?

Best regards,

Bob Masta DAQARTA v6.00 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, FREE Signal Generator Pitch Track, Pitch-to-MIDI Science with your sound card!