Can I use a capacitor balast for neon indicator bulb?

[ELS122]

Why is it always a high resistance resistor used as a ballast for neon bulbs? wouldn't a small value capacitor do the same thing and be cheaper, and more reliable?

[jonpaul]

not good practice, the cap will need a safety rating and pass line transients .

The neon lamps usually fail long before the tiny 1/2 w 100k resistor

j

[chess]

resistor is more cheaper

[Circlotron]

If your mains supply is a perfect sine wave with no noise spikes and you always managed to turn on your neon lamp at the voltage zero crossing a capacitor might be okay. If either of the foregoing occur your neon will likely blow up or fail some other way because noise spikes and turn-on transients are high frequencies that essentially pass straight through the capacitor. The neon will try and clamp the voltage across itself to about 60V or so, similar to a zener diode.

[David Hess]

When the lamp turns on during each half cycle, its negative differential resistance characteristic will draw a large current spike through the capacitor.

[wraper]

Film capacitors in capacitive droppers are way less reliable than resistors which are not overloaded.

[Zero999]

When the lamp turns on during each half cycle, its negative differential resistance characteristic will draw a large current spike through the capacitor.

Yes, this will shorten the life of the lamp and is why inductive ballasts were always used for gas discharge lamps such as fluorescent tubes.

[David Hess]

When the lamp turns on during each half cycle, its negative differential resistance characteristic will draw a large current spike through the capacitor.

Yes, this will shorten the life of the lamp and is why inductive ballasts were always used for gas discharge lamps such as fluorescent tubes.

At high frequency using a capacitor as a ballast works because the lamp never shuts off, but at 50 or 60 Hz the lamp, or at least a neon lamp, has to restart on every cycle.

[vk6zgo]

When the lamp turns on during each half cycle, its negative differential resistance characteristic will draw a large current spike through the capacitor.

Yes, this will shorten the life of the lamp and is why inductive ballasts were always used for gas discharge lamps such as fluorescent tubes.

At high frequency using a capacitor as a ballast works because the lamp never shuts off, but at 50 or 60 Hz the lamp, or at least a neon lamp, has to restart on every cycle.

The current draw of a neon indicator is so low, that a resistor doesn't need to have much of a power rating --capacitors will almost always be more bulky.
That said, I have used a capacitive dropper with an indicator lamp, but a LED,not a neon.
It wasn't off raw Mains, either, but a 65v AC control voltage from a transmitter.

[Circlotron]

Could you use a xenon flash lamp in glow discharge mode, same as a neon? Mild source of continuous light, not bright like a flash?

[Zero999]

The current draw of a neon indicator is so low, that a resistor doesn't need to have much of a power rating

I've found some neon lamps light at such low currents, I can hold both wires and touch the outer sheath of a live wire with the glass bulb and it will flicker and glow dimly.

Could you use a xenon flash lamp in glow discharge mode, same as a neon? Mild source of continuous light, not bright like a flash?

The starting voltage of a strobe is very high, so it would need a step-up transformer to run off the mains.

[David Hess]

The current draw of a neon indicator is so low, that a resistor doesn't need to have much of a power rating --capacitors will almost always be more bulky.

The resistor ends up dissipating about 50 milliwatts, but I always seem to end up using a 1/2 watt resistor for the extra voltage margin.

I think I tried using a capacitor once and the lamp just exploded.