Humming Dimmer

[mkgrady]

A customer complained of a high pitch hum on a 3 way dimmer. She asked me to change the dimmer. It is better but the new one still makes noise. It seems louder at the bulb than at the dimmer. It is running a 200 watt incandescent bulb in a fixture over a kitchen table. I could not find a max rating on the lamp holder but I suspect it is rated no more than 100 watts. I suggested she put a 100 watt bulb in it to see if the noise stops.

I have heard this type of noise when dimming cfl's but not regular bulbs. Any ideas what could be causing the high pitch noise?

 

[LEO2854]

A customer complained of a high pitch hum on a 3 way dimmer. She asked me to change the dimmer. It is better but the new one still makes noise. It seems louder at the bulb than at the dimmer. It is running a 200 watt incandescent bulb in a fixture over a kitchen table. I could not find a max rating on the lamp holder but I suspect it is rated no more than 100 watts. I suggested she put a 100 watt bulb in it to see if the noise stops.

I have heard this type of noise when dimming cfl's but not regular bulbs. Any ideas what could be causing the high pitch noise?

Well did you tell her that that 200 watt lamp is a fire hazard if the fixture is not rated for it.?

Also CFL's must be the dimmable type and the dimmer switch should be rated for CFL's

Also most regular light fixtures are only rated for 60 watt lamps.

 

[cpinetree]

Some lamp filaments resonate if the filament is strung through just a few supports inside the lamp.
Often the large wattage lamps only have 2 or 3 filament supports. I have seen smaller (as low as 15w lamps hum if dimmed down to low)

 

[mkgrady]

Well did you tell her that that 200 watt lamp is a fire hazard if the fixture is not rated for it.?

Also CFL's must be the dimmable type and the dimmer switch should be rated for CFL's

Also most regular light fixtures are only rated for 60 watt lamps.

I told the home owner to determine the max wattage and not exceed it. She removed the sticker and can figure it out from where she bought the fixture.

This fixture likely can handle a bulb larger than 60 watts. It is totally open and there is no place to trap heat.

Even dimmable CFL's with CFL rated dimmers make noise. I'm asking why a standard bulb and dimmer would make a high pitch noise

 

[kwired]

I told the home owner to determine the max wattage and not exceed it. She removed the sticker and can figure it out from where she bought the fixture.

This fixture likely can handle a bulb larger than 60 watts. It is totally open and there is no place to trap heat.

Even dimmable CFL's with CFL rated dimmers make noise. I'm asking why a standard bulb and dimmer would make a high pitch noise

I can't tell you exactly what is happening but am pretty sure it has something to do with the distorted current wave form created by the dimmer. The dimmer is not a resistor, it is a solid state device that simply cuts the peaks off the current wave to reduce effective voltage to the lamp and this makes the lamp dimmer.

 

[LEO2854]

I told the home owner to determine the max wattage and not exceed it. She removed the sticker and can figure it out from where she bought the fixture.

This fixture likely can handle a bulb larger than 60 watts. It is totally open and there is no place to trap heat.

Even dimmable CFL's with CFL rated dimmers make noise. I'm asking why a standard bulb and dimmer would make a high pitch noise

What is the dimmer wattage?

 

[mkgrady]

What is the dimmer wattage?

600 watts. And BTW it hums at full brightness. Not as much as when dimmed but you can still hear it

 

[cpinetree]

600 watts. And BTW it hums at full brightness. Not as much as when dimmed but you can still hear it

I would try some different types of lamps, maybe a par lamp and a 40 watt A19, just to see if it is the lamp causing the hum or if it is the dimmer.

What model dimmer?

If it is a Lutron call their help line, they are pretty good once you get them on the phone.

 

[texie]

I also have found that filamament rattling sometimes goes away or reduced just by changing lamp brands and/or sizes.

 

[Besoeker]

I can't tell you exactly what is happening but am pretty sure it has something to do with the distorted current wave form created by the dimmer. The dimmer is not a resistor, it is a solid state device that simply cuts the peaks off the current wave to reduce effective voltage to the lamp and this makes the lamp dimmer.

The more common units use SCRs or triacs and are sometimes called "leading edge" because they cut off the first part of the sine wave voltage on each half cycle. Might be more accurate to say doesn't let part of it through to varying degrees:

The sharp leading edges might be what's causing the audible hum.

 

[LEO2854]

600 watts. And BTW it hums at full brightness. Not as much as when dimmed but you can still hear it

Maybe a 1,000 watt dimmer will help.

 

[kwired]

The more common units use SCRs or triacs and are sometimes called "leading edge" because they cut off the first part of the sine wave voltage on each half cycle. Might be more accurate to say doesn't let part of it through to varying degrees:

The sharp leading edges might be what's causing the audible hum.

I could see that causing more hum than just cutting the peaks. I would think the better dimmers maybe find a way to smooth the wave a little

 

[Besoeker]

I could see that causing more hum than just cutting the peaks.

As far as I know there is no system that just cuts the peaks.

I would think the better dimmers maybe find a way to smooth the wave a little

I think sine wave dimmers do exist.
It's not my area of expertise. As a group lighting control is a fairly big segment for us.
I don't generally get dragged into it except when things go a bit wrong.

 

[PetrosA]

I'm going to second or third (or whichever I am...) the bulb as the culprit. Filaments are wound like springs and just like springs they make noise when they vibrate. Any dimmer that chops up the sine wave is basically turning the lamp on and off which stretches and contracts the filament, making it vibrate like a guitar string. I use only rough service and fan/appliance bulbs and good quality PAR lamps which seems to help minimize the hum. Someone mentioned in another thread that most dimmers now don't have a 100% setting anymore to comply with CA laws which explains why the bulb hums even at the highest setting. If you bypass the dimmer the hum should stop. Other than that, try different bulbs.