Incandescent Lamp Resonance

Shades of epileptic sensitivity...

Audible outside the car. Radio was fine.

Graham H

I'll amend my statement by saying that many old auto radios' illumination lamps shared a ground with the audio/r.f. circuitry. If you try to PWM one of these, filtering may not help much. But that's still a power supply design issue.

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as far as I know several high-end Audis come with LED headlights as standard

-Lasse

The Audis have LED side lights (running lights); the actual headlights are still incandescents.

ts

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you can get all LED headlights on an R8 everything including high and low beams are LEDs

-Lasse

Can you actually *get* one of those (Audi R8 V10) yet?

:Because I've written about a dozen magazine articles on dimmers and for SOME :PWM frequencies at SOME pulse widths for SOME lamps the filaments heat and :expand, then cool and contract, then heat and expand ... : :With some filament construction (mostly those rather small ones that don't :have a center "hangar" for the filament) this expansion and contraction gets :the filament to swinging about merrily. : :I was just hoping that somebody had done their master's thesis on it and :would have a better handle on it rather than my admittedly unscientific :observations.

Perhaps paying for this document will help enlighten your understanding of the situation.

A long time ago I made a buck regulator with no output filter that crudely regulated the RMS output voltage. Connected it to a small sealed beam spotlight, and although the voltage control was fine, the filament started to sing immediately, and blew when I brought it up near rated voltage. Resonance certainly can be a problem. I never knew whether it was from thermal or magnetic effects. Tony

And there will be aftermarket replacement devices with a choke in them ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

~ Thomas Jefferson

Perhaps if the abstract were in English I might be persuaded to buy the document. As it is, it sounds like it was translated from the Hungarian into the Japanese into the Swedish and thence into the English.

Jim

-- "It is the mark of an educated mind to be able to entertain a thought without accepting it." --Aristotle

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My coworker "Iggy" has an infinity with LED headlights. Replacement cost around $1700. Production luxury cars. I expect that they are also avilable on some BMW and MB. .

:Perhaps if the abstract were in English I might be persuaded to buy the :document. As it is, it sounds like it was translated from the Hungarian :into the Japanese into the Swedish and thence into the English. : :Jim

At least somebody has done some research into the problem - which is what you were after anyway. The language translation problem often occurs in engineering but that hasn't stopped people from following the meaning.

you

engineering

A few years later ; ) but worth adding some info as a reference, in case anyone is interested. According to a paper, "Lamp Acoustical Noise and the Reverse Phase Controlled Dimmer", it says "In a process known as magnetostriction, the filament supports abruptly shorten in length, shaking the entire lamp."

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The larger the filament (or heavier current), the more noise. Happened more at the start of incandescence when the filament is still a lower resistance (rises about 10x at operating temp) and stiff.

I remember going past a head-shop ages ago where they had a clear bulb with a long arched filament which straddled a magnet. The filament would oscillate back and forth on its own. US Patent #3237053 seems to be the original. Others cite this as a reference. (google patents)