DIYbanter - View Single Post - Fluorescent lights cause buzzing in intercom system

gregz

wrote:
On Mon, 06 Feb 2012 12:12:04 -0600, wrote:

On Sat, 4 Feb 2012 19:36:29 -0800, "walter"
wrote:

Ever since I installed a 7-station intercom system (hard-wired), 20 years
ago, I had an annoying buzz when I used the system in the evening, i.e. when
three kitchen fluorescent lights were on. The intercom does not buzz when
the lights are off. I am not referring the slight buzzing noise that comes
from the T-12 ballasts, I am referring to the induced buzzing in my
intercom.

How can I eliminate this type of 50-cycle interference? Can I put filter
capacitors in line with the ballasts? How about replacing the old T-12
ballasts with new electronic ballasts and T-8 fixtures? Would that help? I
believe modern ballast operate at a very high frequency. Maybe I should
connect the intercom master unit (also in the kitchen) to a different
electric circuit?

After 20 years, I am getting mighty tired of all this buzzing in the
evening. Of course, it only buzzes when I actually use the intercom to
answer the door or to suggest to my wife to fix dinner.

Thanks for any suggestions from those who have been there, done it.

Walter

Capacitors are cheap. Go to Radio Shack or elsewhere. Buy some ceramic
caps in the range of .01 to .05, at least 500volts. Put them across the
ac line right where the wires enter the ballasts. If you dont want to
screw around doing all of them, just do one and disconnect the other
ones. It could be just one light causing it too. Disconnect them one
at a time.

Maybe the intercom should have had shielded wire going thru the walls???

If nothing else, try an electronic ballast on just one light, shut off
the others and try it.

For car radio buzz from the cars ignition they make filters for the 12v
lead. Of course you cant use them on 120v, but they may sell a 120v
version. That would also be a capacitor, but has a choke too.

Thid might be a question to post to one of the electronics newsgroups
too.
Nobody has asked - does this intercom connect directly to the 115v
AC or does it have a transformrt?? Many run off of a transformer like
a doorbell. Possible the filter capacitors in the low voltage power
supply section are bad.

Nobody has answered the question either about whether twisted pair
wiring was used to connect the stations - twisted pair provides common
mode noise rejection which can eliminate induction coupling of the
inputs to power lines, and also reduces the "antenna effect" which
picks up hum from things like flourescents.

Also, are all the flourescents GROUNDED???

Unless Walter comes back, we may never know.

Twisted pairs would help, but if the circuits are not balanced on both
ends, only ferrite clamps will help.

I pretty much gave up on getting rid of household wiring noise. It's so
prevalent.

Greg