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What does the blue lead on a magnetic ballast do? Answered

I have a ballast that I want to connect to a transformer, The ballast has two red leads, a black lead, a white lead, and a blue lead. I have no idea what the blue lead is for, or if it's even necessary. Can someone help?



Best Answer 7 years ago

A ballast is a transformer with built in features to change the phase of the
lamps so as a group they do not flicker.
A fluorescent light changes intensity 120 times a second USA or
100 times a second UK ( each reversal of the AC main )

As one lamp is powered at full intensity while the other is going through
its minimum intensity.  The phosphors which cover the inside of the
lamp tube and convert the mercury plasma to visible photons also
provides a little light retention during AC reversal.

Thanks to AndyGadget's pointer, I rearranged the colors in the below
picture to what makes sense to me.

Mind you, my advice is base solely on your description. Test it in a safe
place first, use safety eye protection and after a few minutes turn it off
and carefully smell then feel if it was too hot ! 
Your ballast could be defective.



I'm hoping to connect this to a high voltage transformer. What leads would I have to hook the ballast up to for it to work? (Would it work?)

Doubtful, the ballast is a ferroresonant air-gap transformer.

This type of xfmr has a high voltage no-load output ( when the lamp is off ).
When the lamp begins to plasma ( light up ) and conduct some current.
The transformer drops into current limit ( just like a Sola ) limiting the tube
mercury plasma from growing huge and melting the glass.
The ballast runs two such lamps, one with a leading phase angle and
the other lamp a lagging phase angle. Now the double light flickering is
Not Bad For a Unassuming Ballast Transformer, I think !!

Putting a high voltage transformer in place of a lamp probably wont do
very much, depends on the input impedance of your xfmr.


Actually, my ballast is a magnetic ballast. From what I've read, they just use reactance to limit current flow and usually do not step up the voltage in any way. I don't think that it is designed to drive two lamps.

Now that I think about it, is the ballast really necessary? The transformer doesn't have much resistance (I don't know the primary's inductance), so I thought a ballast would help limit the current flow. Am I being stupid?

Magnetic means transformer the wiring colors makes it a dead ringer self
starting ballast.
Only called Ballast because a ferroresonant air-gap transformer is a mouthful.


Different manufacturers use different colour schemes so you need to Google for the one specific to your ballast.  Is this to drive a fluorescent light unit, or for some other purpose?  I hope you're bearing in mind that mains electricity can have a dramatic effect on your lifespan.