On 19/12/2012 12:09 AM, klem kedidelhopper wrote:
I've been reading the other thread about Quartz halogen lamps and have
found it very interesting. However since this is a bit off that track
I've started this new thread.

I seems like in the last few years it has become impossible to buy
small Christmas light series strings that have conventional lamps in
them. IE: When a filament goes out they all go out. I've noticed that
"something" happens to these new lamps that effectively makes them a
dead short when the filament opens. This then maintains the continuity
of the string and keeps the other lamps lit. But of course this comes
with a high price. A higher voltage is placed across each of the
remaining good lamps when this happens.

Little by little as they over cook, and each filament reaches the
premature end of it's life and opens, that lamp is essentially
replaced by another dead short, thereby running the remaining good
filaments at even a higher voltage. Naturally catastrophic failure of
all the rest of the string is inevitable and systematically occurs
unless this "shorting" action fails on a particular lamp and it
actually "opens". Then the remaining lamps are spared.

I know this is what's happening because I've tried to repair several
strings like this. Last night I looked at two identical 50 lamp
strings. One had about six lamps out with one open. There were 35
lamps out on the other, all with with shorts across them except for
one that was "open". The remaining lamps were still good.

My wife seems to think that not having all the lights go out when one
filament opens represents convenience, and trying to explain series
circuit theory to her is an exercise in futility. So anyhow I now have
one string which I've added 8 additional lamps to for a total of 58
2.4 V lamps on it. It runs a bit dimmer but it should last a lot
longer. I also now have a few spare lamps as well.

As much as it ****es me off you have to give the Chinese credit for
figuring out a way to sell more Christmas lights under the guise of
"convenience".

Does anyone know what is actually happening in these lamps to turn an
open filament into a dead short and begin this "runaway" effect? Lenny





Surely the idea is to replace the blown bulb when noticed ??
Why wait until the situation you described develops ??