# Capacitor as Ballast for gas lamps

## Main Question or Discussion Point

Hi All, :)

Just wonderin'... why can't one use a capacitor instead of an electromagnetic choke as current limiting ballast for gas lamps? A capacitor has very little power loss as core losses are not present. The dielectric losses would definitely much less than power loss in magnetic core of an electromagnetic ballast.

This way we would get very efficient & energy saving lighting systems!...what say?

Regards,
Shahvir

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Partially evacutated gas-filled tubes (fluorescent lamps) have a highhttp://en.wikipedia.org/wiki/Breakdown_voltage" [Broken], but then switch to a low impedance state when the gas is ionized. A substantial inductor (the ballast) will not allow a quick change in current, as would happen when the gas switches to the ionized state. So the ballast prevents an over-current event.

Additionally the http://en.wikipedia.org/wiki/Ballast_%28electrical%29" [Broken] helps strike the lamp because the lamp appears capacitive prior to striking and so experiences a magnification of voltage due to being in series with the inductive ballast.

A capacitor in parallel with the lamp would tend to have the opposite effect. A capacitor in series might limit over-current but will do nothing to help the lamp start.

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Partially evacutated gas-filled tubes (fluorescent lamps) have a highhttp://en.wikipedia.org/wiki/Breakdown_voltage" [Broken], but then switch to a low impedance state when the gas is ionized. A substantial inductor (the ballast) will not allow a quick change in current, as would happen when the gas switches to the ionized state. So the ballast prevents an over-current event.

Additionally the http://en.wikipedia.org/wiki/Ballast_%28electrical%29" [Broken] helps strike the lamp because the lamp appears capacitive prior to striking and so experiences a magnification of voltage due to being in series with the inductive ballast.

A capacitor in parallel with the lamp would tend to have the opposite effect. A capacitor in series might limit over-current but will do nothing to help the lamp start.
That's correct, but we can have a separate ignitor ckt which will only strike the lamp....current limiting can be carried out by capacitor ballast.. will this work?

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A separate ignitor circuit might work, but it would most likely involve an inductor, and would decrease efficiency. This at least partially defeats your original proposition.

Patent 5495143 was my idea when I worked for Science Applications, so I know a bit about gas discharge tubes.

Patent 5495143 was my idea when I worked for Science Applications, so I know a bit about gas discharge tubes.

Sir, then would you be kind enough to share your patent idea on the forum for everyone's academic interest? :)

Part of the purpose of patents is to disseminate technology. Here is a link to mine: http://www.freepatentsonline.com/5495143.html.

An associate in another part of the company had developed a process of making really sharp points of tantalum disilicide by etching rods of this material embedded in silicon rods. The acid would preferentially etch the edges of the rod, leaving a very sharp point. Reading about this in the company newsletter, I realized that those sharp points would make good electron emitters. So I called that researcher and he agreed. This was born the project that resulted in the above patent.

Part of the purpose of patents is to disseminate technology. Here is a link to mine: http://www.freepatentsonline.com/5495143.html.

An associate in another part of the company had developed a process of making really sharp points of tantalum disilicide by etching rods of this material embedded in silicon rods. The acid would preferentially etch the edges of the rod, leaving a very sharp point. Reading about this in the company newsletter, I realized that those sharp points would make good electron emitters. So I called that researcher and he agreed. This was born the project that resulted in the above patent.
Thanks for the link, but I was expecting more of a technical content to be shared

Regards,
Shahvir

For 60 hertz the usual explanation of why an inductor and not a capacitor is used is that,
the size (and cost) of a capacitor will be much larger (and more expensive) than that for an inductor.
Why don't you pick a capacitor and inductor out and let us know what the size and cost are.

For 60 hertz the usual explanation of why an inductor and not a capacitor is used is that,
the size (and cost) of a capacitor will be much larger (and more expensive) than that for an inductor.
Why don't you pick a capacitor and inductor out and let us know what the size and cost are.
well apart from the cost there might be other technical disadvantages of using a capacitor as ballast as stated earlier. I intend to concentrate moreso on the technical downside of same rather than commercial.