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#37629 - 04/30/04 04:48 PM Bad ballast?
Chester Offline

Registered: 04/24/04
Posts: 11
Loc: Ayden, NC USA
When determining whether or not a flourescent light fixture's ballast(s) are bad, what is the easiest way to tell? Is it a voltage test on the contacts? That would not seem to be it, as a ballast sends varying bursts of voltage to get the arc going inside the lamp, I it true that if a ballast is bad the lamps will not light up at all? I was thinking it may be possible to have partial lighting of new tubes as the ballast is going out...anyway, please let me know what tests and criteria you use in determing if a balllast has gone out. I am only an aprentice here, and appreciate all the great info from you long-time pros....

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#37630 - 04/30/04 05:04 PM Re: Bad ballast?
NJwirenut Offline

Registered: 09/15/01
Posts: 816
Loc: Bergen County, NJ
Ballasts are difficult if not impossible to test directly. If you have an identical ballast to use as a reference, you could use resistance tests to check for shorted or open windings, but that's about it. And with electronic ballasts, there really aren't any "windings" to check. Often, a bad ballast will buzz or overheat, but not always.

Basically, if the ballast has input power, and the lamps, lampholders, and starter (if any) are OK, process of elimination leaves a defective ballast.

#37631 - 04/30/04 05:40 PM Re: Bad ballast?
Bjarney Offline

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
You may want to print this stuff an rathole it in your notebook. [Note charts are available in pdf.]

HID info available at these sites too.

Also, there is a lot of useful info in Scott35’s Technical Reference Area at

#37632 - 05/01/04 01:49 AM Re: Bad ballast?
Trumpy Offline


Registered: 07/05/02
Posts: 8532
Loc: SI,New Zealand
Welcome to ECN,mate!.
I have lots of experience with Fluorescent Lighting.
Invariably my Faults work, means I fix heaps of Under-verandah fittings hooked up to the Street-Lighting circuit, in town here.
So are we talking a Twin tube fitting?
Usually a Ballast will have a reasonably low resistance, our 230V ones over here, have a resistance of 57 ohms when new.
What is the fitting doing?, no light from one tube?, Tube flashing?.
Check the starter and the lampholder contacts first.
Then discount the ballast.
Let's face it, these days if you're not young, you're old - Red Green grin


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