Xenon flashlight bulb bypass capacitor?

[John Doe]

This is my question:
Can a bypass capacitor help increase the life of a xenon bulb? If so
please tell me what general type of capacitor.

If any regular here is familiar with xenon light bulbs, I'm sure this
is a simple question for you.

I just bought a light weight, extremely bright dual Xenon flashlight.
Replacement bulbs are difficult to get. They will be switched on and
off frequently.

They look like medium to large size clear LEDs each with two short
leads. I guess it's six volts per xenon bulb, I will multimeter
voltage/current/resistance stuff if that might help.

The work involved is no problem.

Thank you.

 

[John Larkin]

This is my question:
Can a bypass capacitor help increase the life of a xenon bulb?

Sorry, no.

John

 

[John Woodgate]

I read in sci.electronics.design that John Doe <[email protected].

Can a bypass capacitor help increase the life of a xenon bulb? If so
please tell me what general type of capacitor.

No. But a very low value series resistor would. However, it does reduce
brightness. A more complicated inrush-current limiter would work, but
again there would be a loss of brightness unless you use a relay (or
maybe a selected power FET) to short-circuit a series resistor after a
0.5 second delay.

 

[SioL]

I read in sci.electronics.design that John Doe <[email protected].


No. But a very low value series resistor would. However, it does reduce
brightness. A more complicated inrush-current limiter would work, but
again there would be a loss of brightness unless you use a relay (or
maybe a selected power FET) to short-circuit a series resistor after a
0.5 second delay.

Self-heating NTC resistor?

S

 

[John Doe]

No. But a very low value series resistor would. However, it does
reduce brightness. A more complicated inrush-current limiter would
work, but again there would be a loss of brightness unless you use
a relay (or maybe a selected power FET) to short-circuit a series
resistor after a 0.5 second delay.

How about a coil?

 

[John Woodgate]

Self-heating NTC resistor?

In theory, yes, but I don't know of any that would do the job for a low-
voltage xenon lamp. Might be worth looking round.

 

[John Woodgate]

I read in sci.electronics.design that John Doe <[email protected].

How about a coil?

You mean using an inductor to limit the inrush? I doubt that it's
practicable. The required L/R ratio is too high. I don't know what lamp
you have or what a suitable inrush current limit is, but for a 6 V
supply and a 6 V 1 A lamp, to limit the initial rate of change of
current to 1 A/s, assuming zero cold resistance for the lamp, you need a
6 H inductor. The resistance needs to be well below 0.6 ohm so as not to
affect brightness. OK, the inductor can saturate when the full current
is flowing, but that's still a sizeable inductor.

 

[SioL]

In theory, yes, but I don't know of any that would do the job for a low-
voltage xenon lamp. Might be worth looking round.

I've seen a similar solution offered for a regular 220V mains lamp,
many many years ago (15+ years).
Of course current is a lot smaller there so a few ohms might be tolerable,
whereas for a xenon, probably not.

S

 

[Guy Macon]

Read this:

http://members.misty.com/don/bulb1.html

It answers all your questions about extending the life of
Xenon (Halogen) bulbs.

 

[Fred Bloggs]

Read this:

http://members.misty.com/don/bulb1.html

It answers all your questions about extending the life of
Xenon (Halogen) bulbs.

The optimum methodology for life extension is to not use it all- anyone
can see that.

 

[John Woodgate]

I read in sci.electronics.design that Guy Macon <http@?.guymacon.com/>

Read this:

http://members.misty.com/don/bulb1.html

It answers all your questions about extending the life of Xenon
(Halogen) bulbs.

Xenon lamps and halogen lamps are not at all the same thing. Xenon is a
dense inert gas, which allows a higher filament temperature to be
achieved without excessive evaporation of the filament. Halogens are
highly reactive elements, and in a tungsten lamp set up a transport
mechanism whereby filament atoms that escape from the bulk filament are
returned to it.

 

[Al]

This is my question:
Can a bypass capacitor help increase the life of a xenon bulb? If so
please tell me what general type of capacitor.

If any regular here is familiar with xenon light bulbs, I'm sure this
is a simple question for you.

I just bought a light weight, extremely bright dual Xenon flashlight.
Replacement bulbs are difficult to get. They will be switched on and
off frequently.

They look like medium to large size clear LEDs each with two short
leads. I guess it's six volts per xenon bulb, I will multimeter
voltage/current/resistance stuff if that might help.

The work involved is no problem.

Thank you.

If you can stand the current drain, put a resistor, value to be
determined, across the power switch. The idea is to preheat the filement
without having it glow. This automatically raises the resistance and
reduces the surge when the resistor is shorted out when you put the
switch in the ON position. This had been done for eons in military
aircraft.

The value of the resistor can be determined empirically by putting a pot
in parallel with the switch. Turn the switch OFF. Turn the pot down so
the light lights normally, then back off on the pot until the light just
goes out. Read the value of the resistance on the pot and use the next
higher standard value that for the switch by-pass resistor.

If you can't stand the current drain, replace the switch with a slide
switch that has two positions. In the OFF position, no current flows. In
the first ON position, enough current flows to warm the filament but not
to make it glow. In the second position, the battery is connected
directly to the lamp. The time it takes you to switch from fully OFF to
the ON position and thru the partially ON position will provide a
sufficient delay.

Al

 

[John Larkin]

I read in sci.electronics.design that John Doe <[email protected].


No. But a very low value series resistor would. However, it does reduce
brightness. A more complicated inrush-current limiter would work, but
again there would be a loss of brightness unless you use a relay (or
maybe a selected power FET) to short-circuit a series resistor after a
0.5 second delay.

I've read (an ancient GE appnote, I think) that blinking incandescents
doesn't really reduce their life. They do tend to die at turnon, but
they were just about to go anyhow, so that didn't reduce their life
much.

The resistor would greatly extend life because of the voltage drop.
Life is inverse on something outrageous like the 12th power of
voltage.

John

 

[Guy Macon]

Xenon lamps and halogen lamps are not at all the same thing. Xenon is a
dense inert gas, which allows a higher filament temperature to be
achieved without excessive evaporation of the filament. Halogens are
highly reactive elements, and in a tungsten lamp set up a transport
mechanism whereby filament atoms that escape from the bulk filament are
returned to it.

(Smacks self in the head) D'oh! I have no idea why I gave an answer
appropriate for Iodine after reading the word Xenon. Brain fart, pure
and simple. (hangs head in shame)

 

[John Woodgate]

I read in sci.electronics.design that Guy Macon <_see.web.page_@_www.guy

(Smacks self in the head) D'oh! I have no idea why I gave an answer
appropriate for Iodine after reading the word Xenon. Brain fart, pure
and simple. (hangs head in shame)

If it had been krypton, you would have been just one position out in the
Periodic Table.

Table, of course, is quadrivalent, so the formula for the Periodic Table
is Table(IO4)4.

 

[John Doe]

For what it's worth, here are some specs for the Brinkman MAXFIRE
dual xenon rechargeable flashlight:

.... current at battery terminal is 2.30 amps with both lamps on
.... current at battery is 1.16 amps with only the top lamps on
.... current at bottom xenon bulb when both bulbs are on is 1.13 amps
.... battery voltage is 6.5 volts
.... disconnected xenon bulb resistances are .5 and .6 ohms

The flashlight circuit includes:
.... two electrolytic capacitors
.... three transistors
.... three 1% resistors
.... eight 5% resistors
.... two 1N4... diodes
.... one or two small voltage diodes

Unless all that is for switching, maybe it already includes something
for current regulation.

Here is a blurry picture of the circuit (I need a better camera).

http://f1.pg.briefcase.yahoo.com/[email protected]

"flashlight circuit.jpg"

battery maker is Power One
part number 04G10 or KT625
battery rating 6 volts, 2.5 amp hours

I voided the warrantee, I usually void the warrantee before even
touching a device. Mind over matter.

 

[Don Klipstein]

I read in sci.electronics.design that Guy Macon <http@?.guymacon.com/>


Xenon lamps and halogen lamps are not at all the same thing. Xenon is a
dense inert gas, which allows a higher filament temperature to be
achieved without excessive evaporation of the filament. Halogens are
highly reactive elements, and in a tungsten lamp set up a transport
mechanism whereby filament atoms that escape from the bulk filament are
returned to it.

As it turns out, probably not all that much difference... Many xenon
incandescent lamps are also halogen.

The gas fill in a halogen lamp is an inert gas - argon, krypton, or
xenon - and the halogen content is only some really small percentage.

As for life extension by reducing the inrush current:

Although it is common and obvious that incandescent lamps often, even
usually die during the inrush, in most cases what happens is that an aging
filament has a thin spot that has a temperature overshoot during the
inrush. The filament becomes unable to survive the inrush before it
becomes unable to survive steady operation. And in most cases not by a
whole lot - a "thin spot" that melts during the inrush will usually be
running hotter than the rest of the filament during normal operation, and
will be evaporating more badly, and that situation will be accelerating at
a rate increasing worse than exponentially.
As for the inrush causing actual damage to a filament that is not aged
to the point of being killed outright by the inrush: What I have heard
has been mixed, but I believe in most lamps the inrush does not
significantly damage any that it does not kill outright.

One bit of data: Those NTC thermistors sold to stick onto the tip of
the base of a lightbulb have often been claimed to double the life of the
lightbulb. I once applied one and measured the voltage drop, and found
that the voltage aplied to the filament was reduced enough to increase the
life by about 50% even after the thermistor and the lightbulb had fully
warmed up. Gain of double over 1.5 times, if true, means that reducing
the inrush would only extend the life by a third in typical household use.

Keep in mind traffic signals...

One difference that probably applies to halogen lamps: There is a
mechanism where their filaments could develop thin spots whose temperature
is excessive only during the inrush. The ends of the filament, since they
are cooler than the rest of the filament, may get thinned by the halogen
cycle. Should there be any halogen lamps where this is an actual common
cause of failure, I expect they will have life significantly increased by
reducing inrushes.
I expect this to be more significant with halogens that are dimmed
slightly, since slightly dimming a halogen like doing so with a
non-halogen greatly slows down formation of thin spots caused by
evaporation.

- Don Klipstein ([email protected])

 

[Don Klipstein]

I read in sci.electronics.design that John Doe <[email protected].


You mean using an inductor to limit the inrush? I doubt that it's
practicable. The required L/R ratio is too high. I don't know what lamp
you have or what a suitable inrush current limit is, but for a 6 V
supply and a 6 V 1 A lamp, to limit the initial rate of change of
current to 1 A/s, assuming zero cold resistance for the lamp, you need a
6 H inductor. The resistance needs to be well below 0.6 ohm so as not to
affect brightness. OK, the inductor can saturate when the full current
is flowing, but that's still a sizeable inductor.

Since most filaments experience most of their temperature rise from a
cold start in a fraction of 1/10 of a second, I believe most of whatever
actual benefit there is from inrush protection is achieved if the time
constant is slowed down only to 1/10 of a second. Maybe as long as 1/5 of
a second.

So that 6 H inductor becomes a 1.2 or .6 H one...

Still does not sound practical to me!

I think better to use a power MOSFET that has low resistance, a low
value current sense resistor, and appropriate circuitry to add to this
to achieve a slow increase in current... and see whether or not there is
much gain in lamp life - I doubt it.

- Don Klipstein ([email protected])

 

[John Woodgate]

I read in sci.electronics.design that Don Klipstein <[email protected]>

As for life extension by reducing the inrush current:

Although it is common and obvious that incandescent lamps often, even
usually die during the inrush, in most cases what happens is that an
aging filament has a thin spot that has a temperature overshoot during
the inrush.

The inrush current has a cumulative effect. It isn't claimed to kill the
lamp immediately. Pre-heating is extensively used to combat it, and I
doubt that would be done if there were no evidence that it works.

 

[John Doe]

If you can stand the current drain, put a resistor, value to be
determined, across the power switch. The idea is to preheat the
filement without having it glow. This automatically raises the
resistance and reduces the surge when the resistor is shorted out
when you put the switch in the ON position. This had been done for
eons in military aircraft.
The value of the resistor can be determined empirically by putting
a pot in parallel with the switch. Turn the switch OFF. Turn the
pot down so the light lights normally, then back off on the pot
until the light just goes out. Read the value of the resistance on
the pot and use the next higher standard value that for the switch
by-pass resistor. If you can't stand the current drain, replace the
switch with a slide switch that has two positions. In the OFF
position, no current flows. In the first ON position, enough
current flows to warm the filament but not to make it glow. In the
second position, the battery is connected directly to the lamp. The
time it takes you to switch from fully OFF to the ON position and
thru the partially ON position will provide a sufficient delay.

Asking the other regular group members.

Is that an excellent solution with the only drawback as stated power
source drain? So the small current flow does not wear on the xenon
lamp? (relatively speaking). If so, that sounds really great.

In my flashlight application, an additional switch/resistor is
easily included to short the main switch.

Thanks.

I hope that doesn't sound offensive in any way to the reply author
Al. I'm wondering why that workaround hasn't received
notice/accolades from any other group members. Maybe it's too clear
for questioning or comment? Thanks again.