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From: John De Armond
Subject: Re: Maximum Field Current for Delco 10SI Alternator?
Date: Sun, 30 Mar 2008 18:55:10 -0400
Message-ID: <>

On 30 Mar 2008 16:32:31 -0500, wrote:

>Neon John  <> wrote:
>>... Many years ago Westinghouse researchers developed a heuristic for
>>bulb life vs voltage.  Life varies as the thirteenth power of voltage
>>deviation from the nominal.
>So a 120V 1000 hour bulb run at 240V would last 1000/(2^13) = 0.12 hours?

Maybe, if the voltage is brought up slowly or unless it instaflashes.  OTOH, since a
regular household runs at a fairly high temperature already for good color rendering
and since it has a short design light, maybe not.  Run the lamp at 130 or 140 volts
and see how it conforms to Westinghouse's heuristic.

If you're actually interested in how incandescent lamps behave at overvoltage (I
suspect you're not and that you're just being your usual chickensh*t self but just in
case anyone else is), go to and look for a member
called Luxluthor.  He's done a very extensive several year study of mostly portable
lighting-related lamps operated on over-voltage.  He includes performance curves and
instaflash voltages.  His work includes many small low voltage high wattage
quartz-halogen lamps, typically AV lamps.

Many lamps will go 3X nominal voltage before instaflashing.  Many of those will
operate for satisfactory time periods at the instaflash voltage if brought up slowly,
as with a PWM controller.

>>... I run ordinary 120 volt, 500 watt quartz-halogen lamps on 240 volts.
>>The output is dazzling
>For how long? :-)

Probably 20 to 30 hours on mine.  I've had 2 or 3 fail but all those failures were
infant mortalities.  Once the lamp gets past the first few minutes of operation, it
is good for many hours.  I use those cheap chicom "5 for $5" harbor freight special
lamps.  they've turned out to last as long as brand name ones.

I bring the lamps up on about 145 volts (variac-controlled) for modeling and framing.
I have a push button on a cord that I press just before the exposure.  The button
operates a contactor that switches to the full 240 volts.  They stay at that power
only long enough to meter the light, set the exposure and take the picture.

If you're interested in the details - again, I'm sure you're not - then you can look
around the net for an article I wrote several years ago for a glass art newsletter.
It was a paper publication then but I'm sure it's online by now.


From: John De Armond
Subject: Re: Maximum Field Current for Delco 10SI Alternator?
Date: Mon, 31 Mar 2008 00:41:36 -0400
Message-ID: <>

On 30 Mar 2008 22:54:16 -0500, wrote:

>Neon John  <> wrote:
>>Probably 20 to 30 hours on mine.

Only to folks like you who know just enough about a subject to argue.  The original
paper, a copy of which I have, addresses only conventional tungsten lamps.  I'm not
sure if the halogen cycle had been discovered at the time of publication.

I'm curious whether you'd find it equally interesting to note that a 4 hour
photoflood lamp and a quartz heat lamp designed to operate at maybe 2000 deg K behave
quite differently in response to over-voltage?  Kinda Captain Obvious to me.  It
would probably surprise you to learn that a staple of the studio in the bad old days
was the Sola transformer that made sure the photofloods were getting their exact
rated voltage while no one seems to care much about heat lamps.

>Don Klipstein says:
>>...bulb life is typically inversely proportional to applied voltage
>>raised to the 12th power.  I often see 13.

I probably need to send Don a copy of the paper.  Don's a collator of information so
he publishes only what he's found elsewhere.  He doesn't do original research.  12
and 13 seem to be bandied about the net about equally but the original paper says 13.

Here's a page referencing GE's heuristic.  You might notice that GE's exponent is
13.1 for gas-filled and 13.5 for vacuum.

Can I please, mas'a Nick, champion of all nitpickers, be permitted to round 13.1 to
13 for the purposes of idle conversation?

OTOH, the nomograph (by any chance know how to use one of those, Nick?) here seems to
be using exp 12.

A master nitpicker might also notice that Squidoo claims that the same exponent
applies to all lamp types while the GE heuristic shows different exponents and the
Westinghouse paper addresses only "incandescent" lamps, presumably nitrogen-filled,
given the vintage.

I'm sure you'd agree with me, nick, that none of this has any relevance at all to the
question of whether an alternator field coil in any way behaves like an incandescent

>So if a 120 V bulb lasts 750 hours at 120V, Don might expect it to last
>(120/240)^12x750 = 0.18 hours (11 minutes) at 240V.

BSIBSO (Nick's version of GIGO, BS in/BS out). Or what happens when one knows just
enough to do the math but not enough to apply the data.  Hint: You might note in the
URL above that the GE heuristic is useful for no more than +-10% from the nominal.

BTW, any particular reason you chose 750 hours this time and 1000 hours on the last
round?  Just pullin' numbers out of yer nether region again?


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