Products > Dodgy Technology

Another Aliexpress special, the AC DC eliminator

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5U4GB:
Specifically it's a DC Elimination Power Supply AC DC Blocking Power Supply Board.  Not sure why they go to all that effort when this will do the same thing much more efficiently.

Someone:
Not the most insane thing in the world:
https://sound-au.com/articles/xfmr-dc.htm

Circlotron:
I wonder how one of those things would go if put in series with a fluorescent tube. As the tube ages, and particularly toward end of life, one of the cathodes often gets less emissive than the other, causing both a flicker and asymmetrical conduction because of a certain amount of half wave rectification. With one of these devices attached, the resulting DC component would put a DC offset across the tube and maybe brute force symmetrical conduction again. Or maybe make it worse. Not sure.

Andy Chee:

--- Quote from: Circlotron on July 18, 2024, 06:00:08 am ---I wonder how one of those things would go if put in series with a fluorescent tube.

--- End quote ---
An electronic fluorescent ballast would already contain such a DC blocking capacitor, though given their high-frequency operation, the capacitor can be much smaller.

But in a traditional magnetic ballast circuit, I suspect that aliexpress capacitor will form a tank circuit with the magnetic ballast, resonate to high voltages, and destroy the tube.

johansen:

--- Quote from: Andy Chee on July 18, 2024, 11:39:53 pm ---
--- Quote from: Circlotron on July 18, 2024, 06:00:08 am ---I wonder how one of those things would go if put in series with a fluorescent tube.

--- End quote ---
An electronic fluorescent ballast would already contain such a DC blocking capacitor, though given their high-frequency operation, the capacitor can be much smaller.

But in a traditional magnetic ballast circuit, I suspect that aliexpress capacitor will form a tank circuit with the magnetic ballast, resonate to high voltages, and destroy the tube.

--- End quote ---

No to both of those.

The capacitance needed to allow for a 1vac (dc built up in two separate dc caps) voltage drop under load is of such magnitude that there is no way to make it resonate at anything more than just a few hz, certainly not a less than 2 Q inductor of an old ballast.

Electronic ballasts are, these days, full power factor corrected ac to dc to ac converters, drawing better than .99 pf.

A capacitor in series with the input will simply drop the pf slightly and increase the current, having no effect on the tube.

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