Author Topic: Reducing choke ballast noise  (Read 870 times)
sol
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Reducing choke ballast noise « on: March 27, 2019, 08:18:52 PM » Author: sol
I have several Advance LC-25 ballasts in under cabinet strips. They are a bit on the noisy side. What I hear is not so much the 120Hz hum, but some kind of higher pitched raspy hum. I'm guessing it is a multiple of 120Hz that I hear. Most 120V choke ballasts produce this hum, but on most I need to literally stick my ear to it to hear it. I am planning on taking them apart and tightening the mounting screws, but I am wondering if installing silicone or rubber grommets between the ballast and the channel would help. I am also wondering if there is some kind of paste (similar to heat sink paste) that I could use as an acoustic sealant.

The worst ballast has a new lamp as the original one reached EOL recently. The starter didn't get stuck, and the lamp had about 15-20 minutes max of flashing before I took out the starter because the flashing was annoying.

Thanks in advance for your thoughts.
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funkybulb
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Re: Reducing choke ballast noise « Reply #1 on: March 27, 2019, 10:49:07 PM » Author: funkybulb
in older fluorescent lights they use abestos washer
to help silent the noise.   also the loose ballast channel cover be a problem.  one time I was class room
the buzzing was so annoying.  it drove me nuts
none of the other people can hear it in my class
but me.  and  lights were F96T12 and supported on
two down rods luvered type fixture.  I threw my chair on
top of fixture and chair stuck up there and it silent  the light.
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Medved
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Re: Reducing choke ballast noise « Reply #2 on: March 29, 2019, 03:19:04 PM » Author: Medved
It is most likely some harmonics, 120Hz itself is too low frequency to be radiated from something with a limited movement displacement.
Very often the noise gets "amplified" by a room resonance, then the noise is audible only on some spots and not in others.

First start to look for any loose steel rattling close to the ballast (the ballast leaks its mqgnetic field, which may vibrate things around and if loose, they may be rattling). That includes larger area of plane (without any ridges to reinforce it) steel sheet.

Then try to look inside of the ballast assembly alone (if possible, e.g. if not potted) and check whether isnt loose something there.

Last problem is vibtation from magnetostriction. The ballasts operate near saturation, so some core parts may actuqlly saturate. That means the transitions from/to saturation may exhibit magnetostriction compression/expansion, so vibration and noise. To fight this, you need some dissipative material like the mentioned asbestos, these days to be replaced by a glass fibre cloth orsomething similar. It needs to behave as a rag (so dissipative plastic deformation, not springy like steel or so, to really absorb the vibration energy and not just transform its impedance). Rubber may do the absorbing job, but it is not heat robust enough (usable only for ballast rated for mounting on a flamable surface). A normal cloth is the same...
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sol
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Re: Reducing choke ballast noise « Reply #3 on: March 29, 2019, 03:36:51 PM » Author: sol
OK, many thanks for your insights. Would a silicone washer work (the kind of silicone that is normally used for kitchen utensils that you can put in the oven) ? That would be more accessible at the moment than fibreglass cloth.
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