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fluorescent ballsts
Robb D. VanPutte asked:
<<Say, could someone please shed some light (no pun intended) on the
difference between magnetic and electronic ballasts?
>>
Flourescent bulbs are negative impedence devices, i.e. when the mercury
vapor is cold, the resistance is high and it takes a lot of voltage to
cause ionization. (they have little incandescent filaments in the tube ends
to pre-ionize the mercury). Once ionized, all the active electrons buzzing
in the mercury vapor conduct electricity much better and the resistance
goes down. If hooked to a constant voltage, the current would go up the
hotter the vapor got making the vapor even hotter - a runaway condition
which could lead to an exploding lamp. (Don't try this at home. I warned
you!)
A conventional ballast uses an inductor (or transformer/inductor if the
voltage needs to be changed too) to limit the current. It is made of iron
copper and varnish just like a conventional transformer.
An electronic ballast uses a small lightweight high frequency transformer
driven by a transistorized circuit to provide the current to the lamp.
Electronic regulation is used to automatically limit the current to the
desired operating level. The ballast converts the AC line voltage into high
a high frequency AC current source. (Same principle as a switching power
supply.) The incandescent starter filaments at the end of the tubes are not
required, as the ballast is capable of generating very high voltages to
initially energize the lamp. The ballasts are more efficient than
conventional ballasts.
You will probably have to go to a commercial electrical house or try
somewone like grainger <http:\\www.grainger.com> (I think), to obtain an
electronic ballast.
Paul