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Re: More MH lighting questions....
"My own ballasts are all very quiet. Some people have noisier ballasts.
Not sure why some seem to be louder than others, but that seems to be
A good ballast won't have an audible hum. Period.
A hum is usually the coil resonantly vibrating at an audible frequency,
usually the 60Hz of the household AC supply line. A true electronic
ballast inverts the household 60Hz to something in the tens of
thousands of Hz. The higher frequency is more efficient for some lamps
and means that a smaller coil can be used than at lower frequencies.
Even if the coil in an electronic ballast vibrates, it shouldn't be
audible--even to a dog. Examples of electronic ballasts are those from
Ice Cap (very expensive, quiet, and cool running) and AH Supply
(actually Fulham ballasts for flourescents and very quiet and
inexpensive, but run moderately hot compared to IceCaps).
The coils are in the ballasts to limit the current (amps). Without the
choke coils limiting the current, arcing bulbs such as MH and all
flourescents will take all the current you can give them until they
flash out--they aren't self limiting like incandescent bulbs. The coil
also is used to generate the initial high voltage to create the
electrical arc inside the bulb. So arcing bulbs will have coils. It
is because of this current limiting feature that ballasts are called
"ballasts" in the first place. And coils with alternating current
going through them will hum if not constructed or mounted properly. A
coil that isn't anchored down is called a vibrator (and I mean that in
a nice way).
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