Xenon flashlight bulb bypass capacitor?

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.

I read in sci.electronics.design that John Doe wrote (in ) about 'Xenon flashlight bulb bypass capacitor?', on Sat, 29 Jan 2005:

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

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

How about a coil?

Self-heating NTC resistor?

I read in sci.electronics.design that SioL wrote (in ) about 'Xenon flashlight bulb bypass capacitor?', on Sat, 29 Jan 2005:

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.

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

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.

Read this:

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.

I read in sci.electronics.design that Guy Macon wrote (in ) about 'Xenon flashlight bulb bypass capacitor?', on Sat, 29 Jan 2005:

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.

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

(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.

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).

"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.

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 ( snipped-for-privacy@misty.com)

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 ( snipped-for-privacy@misty.com)

I read in sci.electronics.design that Don Klipstein wrote (in ) about 'Xenon flashlight bulb bypass capacitor?', on Sun, 30 Jan 2005:

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.

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.