Running at half the voltage

J

john stone

Guest
Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But the
mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences running
at the lower voltage? Thanks.
 
john stone forklarede:
Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But the
mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences running
at the lower voltage? Thanks.
Click to expand...
A bit dimmer?

If the resistance of the lamp was independent of the temperature, which
it is not, the lamp would draw 1/2 the current at 1/2 the voltage,
giving 1/4 the wattage, 2.5w.

However, the resistance _is_ dependent of the temperature. Se more at

http://en.wikipedia.org/wiki/Halogen_lamp#Effect_of_voltage_on_performance

But the bottom line: Nothing will fail catastropically, but you may get
much less light than expected. But it may look nice and christmassy :)

Leif
(with a lot of but's ;-))

--
Husk křrelys bagpĺ, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.
 
john stone <459fgp86549@mail.invalid> wrote:

Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But the
mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences running
at the lower voltage? Thanks.
Click to expand...
A halogen lamp on the correct voltage runs the filament hotter than a
standard incandescent tungsten lamp. Without the halogen gas filling,
this would soon cause the tungsten to migrate from the filament to the
inside of the bulb, where it would blacken the glass. The filament
would rapidly become thin and then would break.

At a certain temperature, the halogen will combine with the tungsten on
the inside of the glass. It then floats around until it meets the hot
filament, where it deposits the tungsten back where it came from
(approximately). This depends on having the glass hot enough to allow
the halogen and tungsten to combine, which occurs at near dull-red heat
(which is why quartz glass is necessary).

If you under-run the lamp, the filament will not blacken the glass as
quickly, but the glass will not reach recycling temperature, so any
blackening will remain. The relative temperatures of the filament and
glass will determine whether the life if the lamp is extended or
shortened. The light output will be very muchreduced and lacking the
blue end of the spectrum.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
 
To put it a bit more simply...

A /slight/ reduction in voltage will cause a halogen lamp to burn out
prematurely, because the bulb doesn't get hot enough to initiate the
"recycling" process -- but the filament is still extremely hot.

Half voltage is a huge drop. You should have no problems.
 
On Tue, 11 Dec 2012 12:47:53 -0000, "john stone"
<459fgp86549@mail.invalid> wrote:

Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But the
mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences running
at the lower voltage? Thanks.
Click to expand...
At 6V the halogen cycle won't operate so you'll probably get
discoloration of the bulb after some time and perhaps the bulb won't
last as long (to the degree that it's a trade-off of lower power vs.
the elimination of the halogen cycle). Other than that, it'll
probably be a very yellow light at pretty low intensity.
 
On Tue, 11 Dec 2012 10:17:58 -0500, krw@att.bizzz wrote:

On Tue, 11 Dec 2012 12:47:53 -0000, "john stone"
459fgp86549@mail.invalid> wrote:

Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But the
mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences running
at the lower voltage? Thanks.

At 6V the halogen cycle won't operate so you'll probably get
discoloration of the bulb after some time and perhaps the bulb won't
last as long (to the degree that it's a trade-off of lower power vs.
the elimination of the halogen cycle). Other than that, it'll
probably be a very yellow light at pretty low intensity.
Click to expand...
We run a halogen (over our dinner table) from a dimmer. We seldom use it at full
brightness. It's about 10 years old and still on the original bulb.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
 
On Tue, 11 Dec 2012 08:35:17 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 11 Dec 2012 10:17:58 -0500, krw@att.bizzz wrote:

On Tue, 11 Dec 2012 12:47:53 -0000, "john stone"
459fgp86549@mail.invalid> wrote:

Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But the
mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences running
at the lower voltage? Thanks.

At 6V the halogen cycle won't operate so you'll probably get
discoloration of the bulb after some time and perhaps the bulb won't
last as long (to the degree that it's a trade-off of lower power vs.
the elimination of the halogen cycle). Other than that, it'll
probably be a very yellow light at pretty low intensity.

We run a halogen (over our dinner table) from a dimmer. We seldom use it at full
brightness. It's about 10 years old and still on the original bulb.
Click to expand...
The envelope is probably black by now. Incandescent life goes with
something like the 12th power of, er, power, so it's not surprising.
You'll probably find that it won't last all that long, now, at full
power. It's filament is now on the inside of the envelope.
 
We run a halogen (over our dinner table) from a dimmer.
We seldom use it at full brightness. It's about 10 years old
and still on the original bulb.

The envelope is probably black by now. Incandescent life goes with
something like the 12th power of, er, power, so it's not surprising.
You'll probably find that it won't last all that long, now, at full
power. Its filament is now on the inside of the envelope.
Click to expand...
Actually, it's the 12th power of voltage.

Even a slight drop in voltage causes a big increase in life. For example, a
5% reduction almost doubles the lamp's life (1.85 times). At a 10%
reduction, the lamp lasts 3.5 times as long.
 
On Tue, 11 Dec 2012 09:18:37 -0800, "William Sommerwerck"
<grizzledgeezer@comcast.net> wrote:

We run a halogen (over our dinner table) from a dimmer.
We seldom use it at full brightness. It's about 10 years old
and still on the original bulb.

The envelope is probably black by now. Incandescent life goes with
something like the 12th power of, er, power, so it's not surprising.
You'll probably find that it won't last all that long, now, at full
power. Its filament is now on the inside of the envelope.

Actually, it's the 12th power of voltage.
Click to expand...
Of course.

Even a slight drop in voltage causes a big increase in life. For example, a
5% reduction almost doubles the lamp's life (1.85 times). At a 10%
reduction, the lamp lasts 3.5 times as long.
Click to expand...
 
"john stone" <459fgp86549@mail.invalid> wrote in
news:ka7a21$hdi$1@dont-email.me:

Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But
the mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences
running at the lower voltage? Thanks.
Click to expand...
Halogen has a build in cycle to keep the filament healthy.
That does not work at a lower temperature.
So running it at the wrong voltage will cause it to fail
early.
Other then that, for a decoration a dim bulb is no problem,
 
On Tue, 11 Dec 2012 12:04:13 -0500, krw@att.bizzz wrote:

On Tue, 11 Dec 2012 08:35:17 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 11 Dec 2012 10:17:58 -0500, krw@att.bizzz wrote:

On Tue, 11 Dec 2012 12:47:53 -0000, "john stone"
459fgp86549@mail.invalid> wrote:

Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But the
mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences running
at the lower voltage? Thanks.

At 6V the halogen cycle won't operate so you'll probably get
discoloration of the bulb after some time and perhaps the bulb won't
last as long (to the degree that it's a trade-off of lower power vs.
the elimination of the halogen cycle). Other than that, it'll
probably be a very yellow light at pretty low intensity.

We run a halogen (over our dinner table) from a dimmer. We seldom use it at full
brightness. It's about 10 years old and still on the original bulb.

The envelope is probably black by now.
Click to expand...
No. Why should it be, if we seldom run it full brightness? Filamant evaporation
goes as some insane power of voltage. And when we do occasionally run it at full
voltage, won't the halogen cycle do its thing?


Incandescent life goes with
something like the 12th power of, er, power, so it's not surprising.
Click to expand...

Exactly. Running it at half voltage, or even 3/4 voltage, is almost equivalent
to turning it completely off.

Various references say that incensescent lifetime goes as voltage to the -13 to
-16 power.

You'll probably find that it won't last all that long, now, at full
power. It's filament is now on the inside of the envelope.
Click to expand...
Can't see why. The evaporation rate is 0.5^13 as much at half voltage as at
full. That's essentially no evaporation at all.

Anyhow, it's over 10 years old and works fine. I may never get to use that spare
bulb.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
 
"John Larkin"

Various references say that incensescent lifetime goes as voltage to
the -13 to
-16 power.
Click to expand...

** The formula that predicts lamp life is only valid for a small range
around the nominal voltage, about 10%. The simplifying assumptions it is
based on are true only in this range.

Reducing the voltage by large percentages extends lamp life by factor of 10
or possibly up to 100 - the halogen cycle has SFA to do with it.


.... Phil
 
On Tue, 11 Dec 2012 09:18:37 -0800, "William Sommerwerck"
<grizzledgeezer@comcast.net> wrote:

We run a halogen (over our dinner table) from a dimmer.
We seldom use it at full brightness. It's about 10 years old
and still on the original bulb.

The envelope is probably black by now. Incandescent life goes with
something like the 12th power of, er, power, so it's not surprising.
You'll probably find that it won't last all that long, now, at full
power. Its filament is now on the inside of the envelope.

Actually, it's the 12th power of voltage.

Even a slight drop in voltage causes a big increase in life. For example, a
5% reduction almost doubles the lamp's life (1.85 times). At a 10%
reduction, the lamp lasts 3.5 times as long.
Click to expand...
I guess the question becomes: is there some voltage a bit below normal, where
the halogen cycle doesn't work and lamp life actually degrades? I'm guessing no.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
 
On 11 Dec 2012 18:19:51 GMT, Sjouke Burry <s@b> wrote:

"john stone" <459fgp86549@mail.invalid> wrote in
news:ka7a21$hdi$1@dont-email.me:

Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But
the mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences
running at the lower voltage? Thanks.



Halogen has a build in cycle to keep the filament healthy.
That does not work at a lower temperature.
So running it at the wrong voltage will cause it to fail
early.
Click to expand...
Why? If there is almost no filament evaporation (which is the case at, say, half
or 3/4 voltage) why would it fail sooner? The halogen thing might not kick in at
low voltage, but then it's not needed.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
 
Even a slight drop in voltage causes a big increase in life. For example,
a 5% reduction almost doubles the lamp's life (1.85 times). At a 10%
reduction, the lamp lasts 3.5 times as long.

I guess the question becomes: is there some voltage a bit below normal,
where the halogen cycle doesn't work and lamp life actually degrades?
I'm guessing no.
Click to expand...
I'm guessing yes. A friend had halogen lamps on a dimmer, which he dimmed
only slightly -- and they burned out pretty quickly.

The halogen cycle requires a very high temperature. Ergo...
 
On Tue, 11 Dec 2012 21:47:27 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 11 Dec 2012 12:04:13 -0500, krw@att.bizzz wrote:

On Tue, 11 Dec 2012 08:35:17 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 11 Dec 2012 10:17:58 -0500, krw@att.bizzz wrote:

On Tue, 11 Dec 2012 12:47:53 -0000, "john stone"
459fgp86549@mail.invalid> wrote:

Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But the
mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences running
at the lower voltage? Thanks.

At 6V the halogen cycle won't operate so you'll probably get
discoloration of the bulb after some time and perhaps the bulb won't
last as long (to the degree that it's a trade-off of lower power vs.
the elimination of the halogen cycle). Other than that, it'll
probably be a very yellow light at pretty low intensity.

We run a halogen (over our dinner table) from a dimmer. We seldom use it at full
brightness. It's about 10 years old and still on the original bulb.

The envelope is probably black by now.

No. Why should it be, if we seldom run it full brightness?
Click to expand...
Because you DON'T run it at full brightness the envelope isn't cleared
by the halogen cycle. This is a common failure of halogen bulbs. They
get black, reducing their light output and fail early.

Filamant evaporation
goes as some insane power of voltage. And when we do occasionally run it at full
voltage, won't the halogen cycle do its thing?
Click to expand...
But you just said you rarely run it at full power. It can't if you
don't.
Incandescent life goes with
something like the 12th power of, er, power, so it's not surprising.


Exactly. Running it at half voltage, or even 3/4 voltage, is almost equivalent
to turning it completely off.
Click to expand...
s/power/voltage, as pointed out earlier.

Various references say that incensescent lifetime goes as voltage to the -13 to
-16 power.
Click to expand...
12/16, who's counting.

You'll probably find that it won't last all that long, now, at full
power. It's filament is now on the inside of the envelope.

Can't see why. The evaporation rate is 0.5^13 as much at half voltage as at
full. That's essentially no evaporation at all.
Click to expand...
The halogen cycle stops.

Anyhow, it's over 10 years old and works fine. I may never get to use that spare
bulb.
Click to expand...
There are carbon filament bulbs still operating from a hundred years
ago. <shrug>
 
On 12/11/2012 12:18 PM, William Sommerwerck wrote:
We run a halogen (over our dinner table) from a dimmer.
We seldom use it at full brightness. It's about 10 years old
and still on the original bulb.

The envelope is probably black by now. Incandescent life goes with
something like the 12th power of, er, power, so it's not surprising.
You'll probably find that it won't last all that long, now, at full
power. Its filament is now on the inside of the envelope.

Actually, it's the 12th power of voltage.

Even a slight drop in voltage causes a big increase in life. For
example, a 5% reduction almost doubles the lamp's life (1.85 times). At
a 10% reduction, the lamp lasts 3.5 times as long.
Click to expand...
It's all a curve fitting exercise, and V**12 looks a lot like V**10.(*)
It's often quoted as going like exp(10500/T(K)), where T is the
filament temperature, which goes roughly like sqrt(V). That's a
slightly more physicsy fitting function, but none of them work very well
over any wide voltage range. For instance, the lifetime increase at 10%
below rated voltage is variously quoted anywhere from 3x to 5x.

Cheers

Phil Hobbs


(*) Which is why the Hilbert matrix is so ill-conditioned.

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On 12/12/2012 12:55 AM, John Larkin wrote:
On Tue, 11 Dec 2012 09:18:37 -0800, "William Sommerwerck"
grizzledgeezer@comcast.net> wrote:

We run a halogen (over our dinner table) from a dimmer.
We seldom use it at full brightness. It's about 10 years old
and still on the original bulb.

The envelope is probably black by now. Incandescent life goes with
something like the 12th power of, er, power, so it's not surprising.
You'll probably find that it won't last all that long, now, at full
power. Its filament is now on the inside of the envelope.

Actually, it's the 12th power of voltage.

Even a slight drop in voltage causes a big increase in life. For example, a
5% reduction almost doubles the lamp's life (1.85 times). At a 10%
reduction, the lamp lasts 3.5 times as long.

I guess the question becomes: is there some voltage a bit below normal, where
the halogen cycle doesn't work and lamp life actually degrades? I'm guessing no.
Click to expand...
The bulb envelope cleans up if you run it at full power for awhile anyway.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On 12/11/2012 01:19 PM, Sjouke Burry wrote:
"john stone"<459fgp86549@mail.invalid> wrote in
news:ka7a21$hdi$1@dont-email.me:

Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But
the mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences
running at the lower voltage? Thanks.



Halogen has a build in cycle to keep the filament healthy.
That does not work at a lower temperature.
So running it at the wrong voltage will cause it to fail
early.
Other then that, for a decoration a dim bulb is no problem,
Click to expand...
Nope. The halogen cycle is to keep the envelope clean. The high gas
pressure extends the filament life, by causing tungsten to be
selectively redeposited back on the same hotspots it came from.
Otherwise the tungsten redeposits randomly, and there's nothing to keep
the hotspots from necking down and failing just as early as in a
low-pressure bulb.

(We keep coming back to this every few months lately.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
On Tue, 11 Dec 2012 10:17:58 -0500, krw@att.bizzz wrote:

On Tue, 11 Dec 2012 12:47:53 -0000, "john stone"
459fgp86549@mail.invalid> wrote:

Have a 10Watt, 12Volt Hologen lamp for a christmas decoration. But the
mains tranformer I have is only 6 Volts.

Apart from being a bit dimmer, would there be any other consequences running
at the lower voltage? Thanks.

At 6V the halogen cycle won't operate so you'll probably get
discoloration of the bulb after some time and perhaps the bulb won't
last as long (to the degree that it's a trade-off of lower power vs.
the elimination of the halogen cycle). Other than that, it'll
probably be a very yellow light at pretty low intensity.

We run a halogen (over our dinner table) from a dimmer. We seldom use it at full
brightness. It's about 10 years old and still on the original bulb.
Click to expand...
I got some in my kitchen, range hood, bathroom. I have never experienced
problems on dimmer. Most of the bulbs last long, but you get one occasional
early failure. Except for the range hood which is run full on or full dim,
the others lights are most always run 1/2 to 3/4 brightness.

Greg
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top