I recently installed a large kitchen with 3 pendant lights over the island and 2 pendant lights over the peninsula. The transformers in the pendants seem to be burning out, not the hologen bulbs. The lights are all on the same dedicated 20 amp cuircut. When I went out to replace the lights for the customer I read the directions and it specifically recommended to use dimmers rated specifically for “electronic low voltage” and are sometimes referred to as trailing edge or reverse phase. The sub on the job did not, just a typical dimmer. Could this be the problem? Someone else told me that it is also likely the transformers are working too hard and there may not be enough voltage getting to the lights. One thing I noticed is that when the lights are on or more specifically when they are dimmed they seem to (humm) alot, like something isn’t working right. Any ideas are appreciated.
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The hum is normal (more or less). The failure to use the special dimmers may have caused the transformer failure.
I would
1. use a decent quality dimmer, like a lutron. It should cost at least $15. I can't remember if they specify "ok for low voltage lights" or not, I don't think so.
2. Check the line voltage coming in to the transformer to see that it's not too far off 120.
zak
"so it goes"
1. Hum is not normal in anything other than cheap shop-type fluorescents on the fritz.
2. Get the type of dimmer recommended by the manufacturer of the lighting transformer. Yes, the wrong one will burn the transformer.
3. Next time get a "sub" who is an electrician. This is pretty elementary stuff. Can't imagine an electrician did that, and if he did, why are you fixing it instead of him?
DG/Builder
Was your purpose in answering the thread to give advice or to give a lecture to those of us who don't use the trades? I, for one fail to see the necessity for paragraph 3 of your post.
It was both.
The necessity for the lecture is crystal-clear. The hack who did the job had not a clue and created a potentially dangerous situation for the homeowner. Can you say fire hazard?
I don't know who "those of us who don't use the trades" are. Fill out your profile. If you're a DIY and take out permits, no problem. If you're a contractor like the OP and have electrical work illegally performed by non-electricians, you're a hack and you don't belong on this forum. Notice the word "fine" in FHB.
DG/Builder
Hum is quite normal in dimmed incandescents.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Dan, every single light in my house has been on a dimmer for the last 15 years. Several different types of dimmers. Plain, preset, remote, etc. Not a single hum from any of them ever. It's very quiet late at night and my hearing has been checked recently.
Also no complaints of hum from any customer ever. Don't know what to tell you. Are you saying you hear hum from the dimmer or from the bulb?
The bulb. And generally it's more of a buzz. Worse with very dim settings. Never have quite figured out what causes it.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Many filaments have coiled wire. They form a magnetic field and when the each 1/2 cycle turns off they relax. Then when it fires again the magnetic field moves the coil again.
Yeah, I just haven't figured out why it's worse when dimmed.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Dan, 60 Hz buzz is low frequency audio and as such is very non-directional. Use a mechanic's stethoscope to make sure it's really coming from the bulb and not something else. If it's low voltage, I bet it's coming from the transformer.
If it's really from the bulb, change to a different style bulb, like PAR or something totally different. See what happens. Then make an extension cord for the bulb and plug the original bulb in the original fixture through the cord. You have de-coupled the bulb from the fixture mechanically. See what happens now. The answer should be pretty obvious by then.
Also, just for kicks, try a bulb with a straight filament. Just to amuse Bill :)
DG/Builder
I've heard it coming from 120V incandescents, where the dimmer is on the wall 5-10 feet away.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
> I just haven't figured out why it's worse when dimmed.
It's because the magnetic field is proportional to dV/dt. A sine wave increases and decreases gently, but the dimmer turns on with a much faster rise time. It's worst when it switches at the 90 and 270 degree points, where the rise is highest.
The loose tungsten coil of the filament pretty much resists the outward radial force, but the turn to turn attraction compresses it at each half cycle. It springs back when the rapid rise is over. With a contration on every half cycle, the filament vibrates at 120 Hz. I'm not sure what proportion of what we hear is transferred down the supports to the base and globe, and what proportion goes out thru the argon gas.
The long loose zigzag of a rough service filament will buzz a lot less.
-- J.S.
Bill, I hope you're kidding. That is the biggest crock of BS I've ever heard.
First, in order for a magnetic field to move something, that something has to exist. Like the magnet in a speaker, the plunger in a solenoid, etc. No such "core" piece in a bulb.
Second, that something has to be either ferromagnetic or another electromagnet.
Third, even if the filament were to vibrate very slightly, how would the vibration be transmitted to the outside? There is vacuum inside and only a few floppy wires supporting the filament.
While transformers, balasts and such can vibrate, it is precisely because they have an iron core that is excited by the field. It's the iron that vibrates, not the coil. And the field is many orders of magnitude greater than the negligible field in a bulb.
DG/Builder
Bill is quite right. You don't need any ferromagnetic material, just a coil of wire with current in it. If you don't believe this, check out a physics book.Most light bulb filaments are formed in a tiny helix. The helix will tend to compress in length and widen in diameter when a current is applied.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Bill is quite right. You don't need any ferromagnetic material, just a coil of wire with current in it. If you don't believe this, check out a physics book.
I did, but perhaps I'm dumb :) Give me the name of any physics book where you read this and the page number. Bet you 2 beers on it.
Most light bulb filaments are formed in a tiny helix. The helix will tend to compress in length and widen in diameter when a current is applied.
Yes, it's caused by thermal expansion as they go from room temp to white hot. The thermal mass of the filament prevents it from expanding and contracting at 60 Hz.
DG/Builder
And that may be the cause of the buzz, for all I know.Oh, and it would be Halliday and Resnick, "Physics II", 1962, section 33-3, page 819. "A current is an assembly of moving charges. Because a magnetic field exerts a sideways force on a moving charge, we expect that it will also exert a sideways force on a wire carrying a current."(This is my wife's physics book -- can't find my old engineering books.)
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
"A current is an assembly of moving charges. Because a magnetic field exerts a sideways force on a moving charge, we expect that it will also exert a sideways force on a wire carrying a current."
Yes Dan, that is absolutely correct. And no, it does not mean that the coil creating the magnetic field can move itself.
If you don't understand the theory think in practical terms. There is NO device that moves itself by having just an electromagnetic coil. There is always an iron core, a magnet or another coil that moves.
DG/Builder
I quite understand the theory. If you have the typical coiled filament, each turn of the "coil" can be considered to be a separate coil. Two coils with common axes and current running in the same direction will be attracted to each other. So the magnetic field caused by the current tends to cause the coiled filament to compress in length.I'll admit that I slept through a lot of classes in engineering school, but the electromagnetics prof shouted too loud to let me sleep through that one.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
coils with common axes and current running in the same direction will be attracted to each other.
Which then "pulls" on the support wires, which are firmly attached to the bulb base . . .
Ok, now that we have clamored on on the physics of an incandescent lamp--what do we tell OP who is likely wolking with halogen units (and very probably LV halogens at that)?Occupational hazard of my occupation not being around (sorry Bubba)
> ... the physics of an incandescent lamp--what do we tell OP who is likely wolking with halogen units ....
Halogen lamps are incandescent. They consist of a tungsten filament and a halogen gas (bromine or flourine IIRC) in a quartz envelope. Conventional lamps consist of a tungsten filament and argon gas in a borosilicate glass envelope, the same common glass used for windows and bottles.
-- J.S.
Halogen lamps are incandescent.
True enough, but dimensionally & structurally quite different than one's 60W medium base lamp, too.
Just seemed a tad wastefull to be bashing at each other over physics trivialities when we could be stompin' on contractor-bashers <g> . . . Occupational hazard of my occupation not being around (sorry Bubba)
Acutally, Philips here market a line called "Halogena", which are basically small halogens packaged double-jacket inside a borosilicate globe with a medium base, giving them pretty much the external form of a conventional inky. It's the filament forms that count, though.
-- J.S.
Philips here market a line called "Halogena"
Yeah, I've seen those, just haven't had an application that warranted spending the cash to try any out my own self.
I've used the Sylvania "Halogen" 35W I/O floods--but I've found them to be "cranky" about their environment. They appear to be very sensitive to voltage changes.Occupational hazard of my occupation not being around (sorry Bubba)
And further, the current through halogen bulbs is higher for a give wattage, so there's a potential (other geometries being equal) for even more magnetic effect. True, the filament will likely have fewer turns, but not 10x fewer. Rather, the filament wire will be heavier to produce the lower resistance at the lower voltage.Assume, for example, that the filament has 1/3 the turns of a 120V filament. It will carry 10x the current and each turn will have 10x the magnetic field (actually more, since the turns will likely be larger diameter), so the net effect would be about 3.3x more magnetic field than the 120V unit.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
> the current through halogen bulbs is higher for a give wattage,
You mean for those low voltage halogens. The 120 Volt ones would have exactly the same current as inky's of the same wattage.
-- J.S.
True
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Have you ever seen welding cables jump when the arc is struck? That is the magnetic field at work.And look at this thread and the following messages.http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=73579.14&search=yhttp://psroc.phys.ntu.edu.tw/cjp/v35/139.pdf
Have you ever seen welding cables jump when the arc is struck? That is the magnetic field at work.
Bill, you should have quit while you were only looking dumb. This is just plain stupid.
No, I haven't seen welding cables jump except when a novice welder got startled by an arc.
Just think of how stupid this is before you embarrass yourself. If cables were to move when a couple of hundred amps pass through them, then the overhead power company cables carrying thousands of amps should be doing the cha-cha 24/7.
DG/Builder
Yes, I look dumb. But where have you seen a picture of me.But LOOKS ain't everything.You had to go and prove how dumb you are.Clearly you did not look at the lines that I posted.But maybe, in the meantime, you have learned enough to be able to clicks on a link.http://www.exploratorium.edu/snacks/circles_magnetism_IV.htmlhttp://istp.gsfc.nasa.gov/earthmag/oersted.htmThe first link show science experiments for elementry students. Maybe you could find one to explain it to you."If cables were to move when a couple of hundred amps pass through them, then the overhead power company cables carrying thousands of amps should be doing the cha-cha 24/7."Look at the 2nd link. What is R?
dgbldr:Welding cables DO move when large currents rush through them.
That is because there are two of them, and the lines of magnetic force caused by the inrush of current pushes against the lines of magnetic force in the opposite cable. There may also be a reaction of the magnetic field to the earth's magnetic field with one wire. Remember, we are sitting on a large iron core called earth!You can also get jumper cables to move from magnetic force. There is no difference in the science of the welding cables moving than how an electric motor works. Current through a wire produces a magnetic field. Iron core or no iron core. The iron just effects effiency and other parameters.And to your final statement, Yes, I have seen the overhead wires move with respect to each other when a large inrush current goes through them.Frank DuVal You can never make something foolproof because fools are so ingenious.
OK folks, might as well make a project of it now. Let's calculate the maximum instantaneous electromagnetic force between two adjacent turns (loops) of a bulb's filament:
F= (mu * I1 * I2 * L)/(2 * Pi * D)
mu is permeability of free space = 4 * pi * 10^-7
For a 100W bulb, currents are I1=I2= 1.4A peak
L = circumference of the turns, roughly = 2mm
D = distance between turns, roughly = 0.5mm
When you do the arithmetic, I get 1.6 microNewtons, or 0.36 microPounds-force.
You think you can stretch that filament with 0.36 MILLIONTHS of a pound?
And of course, for a lower wattage bulb, note that the force goes down with the square of the current.
And last, for the common sense part of this BS theory of stretching the filament: If that filament were to stretch 60 times a second by an amount sufficient to cause vibration and audible buzz, how long do you think it would last?
Actually, it isn't stretched, it's compressed.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Actually, it isn't stretched, it's compressed.
Yes, pardon my typo. It is compressed. So how about answering the question instead of nitpicking? You think you have enough force to compress the filament?
Tell you what. I calculated the force for you. See if you're capable of calculating how much force it takes to compress the filament. Pretty trivial mechanical calculation. Can you do it?
Then we can all see if your theory holds any water.
DG/Builder
Actually, I never said it was enough force -- never thought it was important enough to bother with the computations. But I'd point out that the force you calculated is between EACH adjacent pair of loops, so the total force end-to-end would be that amount multiplied by the number of loops (minus one, I suppose).I wouldn't swear that a force on the order of a millionth of a pound was sufficient to make noise. Wouldn's swear that it wasn't, either. I've often been amazed at how much noise can come out of very low-power devices.All I said is that some bulbs hum/buzz when dimmed (a certain fact), and that I wasn't sure why. It could be thermal effects, cosmic rays, Martians, whatever. Others kicked in the suggestion that it was magnetic effects.But, as to magnetic effects, have you ever seen a "flicker" bulb (simulated candle). Some are neon, but some are incandescent and consist of a filament held in a loop by fairly springy support wires. In the center of the loop is a small permanent magnet. The magnetic effects between the filament and the permanent magnet are sufficent to cause the filament to wobble back and forth at about 5 Hz, creating the flicker effect. And that's only a maybe 25W bulb.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
All I said is that some bulbs hum/buzz when dimmed (a certain fact), and that I wasn't sure why. It could be thermal effects, cosmic rays, Martians, whatever. Others kicked in the suggestion that it was magnetic effects.
Yup, I got that. Personally, I would have spent half an hour to figure why and fix it. Some people make things happen, some watch things happen and some wonder what happened.
Enjoy your buzz :)
DG/Builder
Try rough service bulbs. The same filament designs that make them more shock resistant also make them hum less. It's the tight coils of an ordinary filament that act as a solenoid, plus the rapid rise time of the triac dimmer that cause vibration.
-- J.S.
I think he was talking halogen bulbs. The guy I work with installed similar pendant halogen lights on a job and had the same problem. I think the cheap dimmer switch burned out the transformer. (I wasn't involved with the electrical intallation.)
Many issues.
"Could this be the problem? Someone else told me that it is also likely the transformers are working too hard and there may not be enough voltage getting to the lights. "
Who is that someone and why do they think that the transformers are "working too hard". Note - transformers don't need breaks or get overtime pay. Nowever, they rated by the load that they can handle. If they are overloaded or run near rated load they will have reduced life.
What are the transformers rated for? How many and what wattage bulbs re on each one?
"Not even voltage" getting to the lights is not a cause, but might be a symptom of an overloaded transformer. Have you measured the voltage?
If this are so called ELECTRONIC transformers you should have hear any hum at any light setting.
If they are magnet transformer then you might.
While typically either type of transformer will work with most dimmers there are ones specifically designed for each type of load.
Lutron makes the different ones in most of their lines. In most cases you will need to go to an electrical distributor to get them.
Here is one line from Lutron. Scrol down and you will see the ones for electronic transforms and ones for use with magnetic transformers.
http://www.lutron.com/ariadni/default.asp