Re: Ballast Transformers.

To: tesla-at-pupman-dot-com
Subject: Re: Ballast Transformers.
From: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Thu, 09 Mar 2000 13:48:59 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi Mark,

> Original Poster: "Mark Broker" <broker-at-uwplatt.edu>
> A ballast is a small step-up transformer.  But, the power-handling is
>very low.  I think on a standard 4' light ballast, the voltage is only
>a couple kV.
>The current is also quite low (a 4' flourescent bulb is rated ~50W).
>I was told that a ballast also modifies the frequency, or rectifies it,
>but I have seen slow-motion pictures that show the lights flickering
>at about 60Hz.....

A few corrections to the above post ;o))

A ballast is NOT a transformer (although one can use an xformer as
a ballast). A ballast has only ONE winding. In a fluorescent lamp a
ballast does two things: First of all, it limits the maximum current
that can flow (an "ac resistor") and second of all, it provides a
starting "kick" for the lamp (they need HV to ionize the gas/mercury
vapor inside the lamp). However, this HV "kick" is NOT due to
"transformer" action, but rather that the inductor stores energy in
the form J=0.5*L*I^2. In other words, the inductor tries to keep
the same current flowing as you open the windings. It does this by
raising the voltage (Ohm´s Law). Also, a ballast will do NOTHING
to the frequency or towards rectifying the AC voltage. At a certain
frequency, the ballast will appear to have zero ohms (not including
the resistance, the copper wire has). This is called the resonance
frequency, but it cannot change the applied frequency. It can´t
rectify the AC, because it basically is nothing more than a coil of
long wire.


Coiler greets from Germany,
Reinhard