What is a Volt-Amp? (Doorbell Transformer Question)

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  #1  
Old 02-09-06, 06:42 AM
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What is a Volt-Amp? (Doorbell Transformer Question)

I want to replace my doorbell transformer because it hums very loudly. The doorbell works fine but the noise is terrible. The transformer says 16V, 30VA. I went to Lowes and Home Depot and they both have 16 volt transfomers, but not with 30 volt-amps. Do I have some kind of weird setup here? I only have one button and one non-elaborate bell in the system. Could I use a transformer that is 16V, but 10 or 15 VA?

Thanks
 
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  #2  
Old 02-09-06, 07:19 AM
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You can use the Internet to find definitions for just about any term.

Here is one for volt-amp:

The measurement of electrical power that is computed by multiplying volts times amps. In a DC circuit, volt-amps (VA) and watts are the same because DC circuits do not add inductance and capacitance that take away power. In AC devices, volt-amps ratings are higher than watts. For example, in an uninterruptible power supply (UPS), the volt-amps rating is approximately 60% higher than the actual wattage

When discussing power, you need both the current and the voltage. Your existing transformer is more powerful than the one you have found at the big box stores.

Will a smaller one work? Most likely. You can always try it and see.
 
  #3  
Old 02-09-06, 07:34 AM
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Originally Posted by racraft
Will a smaller one work? Most likely. You can always try it and see.
So I guess I'll try the 16V, 15 VA transformer. If it rings the doorbell, I guess I'm OK.

Thanks.
 
  #4  
Old 02-09-06, 07:44 AM
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Hi, 16 volts is the common tranformer voltage for doorbells. The volt-amp (watts) rating of the transformer should be equal to or greater than the wattage requirement of the buzzer or chime unit. 30 VA is usually a tansformer used with chime units and just the ole ding dong bells are as low 10 volt amps. Hope this helps.
 
  #5  
Old 02-09-06, 08:30 AM
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I'll probably pull the cover off the bell and see what it says, but I suspect 30 VA is overkill for this application.

Am I right to expect this transformer to not hum so loudly?
 
  #6  
Old 02-09-06, 08:33 AM
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The transformer is getting old and wearing out. Yes, it needs to be replaced.
 
  #7  
Old 02-09-06, 08:37 AM
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Thanks guys.

I'll give it a shot tonight.
 
  #8  
Old 02-10-06, 06:42 AM
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The Good News:
I replaced the doorbell transformer and it works fine!

The Bad News:
That little SOB still hums loudly!

If I exert pressure on the transformer is gets pretty quiet, so I am guessing we are talking about a vibration problem. What is a safe way to mount this thing so it won't do this?

My current setup:
I have a metal box screwed into the wooden underside of stairs. The transformer butts up next to the box and attaches to it. There is a pull chain light on the box as well.

Also, the transformer is warm, not hot - is that normal?

Thanks
 
  #9  
Old 02-12-06, 06:28 PM
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How is the transformer mounted today? Transformers vibrate. If it's touching the box - maybe that's what you're hearing. Transformers also get warm. You may have a problem with the chime unit itself - or the door bell switch.... Have you made other changes that could effect the transformer?
 
  #10  
Old 03-16-06, 07:00 PM
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The following suggestion may not meet code but it is what I would consider doing. I will assume the transformer you bought has a male conduit nipple attached that fastens to the box. At many HDs they now sell ENMT. It is a flexable plastic conduit (looks a bit like blue BX). You will need about two inches but unfortunately it is sold in 10 foot lengths. It's cheap though so the waste won't be that costly. You will also need one female and one male half inch threaded ENMT adapter.

Most transformers have a built in bracket on the base for fastening it to a surface with screws. Use the short length of ENMT to connect the transformer to the junction box, running the wires through the conduit . (Female ENMT connector screws on to the transformer nipple and the male goes through the knock out hole in the junction box.) Place a rubber pad made from a material such as auto gasket material between the transformer and the wood and screw down the transformer.
 
  #11  
Old 03-16-06, 08:45 PM
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> The following suggestion may not meet code

It doesn't.


> but it is what I would consider doing.

Only if it meets Code.


> It is a flexible plastic conduit (looks a bit like blue BX).

Smurf tube.


> You will need about two inches

Or how ever far away you move the box.


> Place a rubber pad made from a material such

You may mount the xfmr in a separate box and attempt to acoustically isolate it.


> screw down the transformer.

Screw down the box using rubber grommets around the screws and not too tight.
 
  #12  
Old 03-17-06, 08:28 AM
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There's something wrong with your circuit. Mounting a doorbell transformer to a metal box with a pull chain fixture is very common, and shouldn't create a noise problem, if all the screws and locknuts are tight.

Does the transfromer buzz loudly all the time? If you remove the wires from your chime, does it still buzz? If you remove the wires from your button, does it still buzz? My guess is you have a high resistance short circuit in your bell circuit (a solid low resistance short would burn the transformer out instead of creating a noise problem). If the short isn't created in the equipment, it could be in the wires. You could have a staple that is shorting out the wiring. You need to isloate all your components, including the wire, to see which is the culprit.

Is it possible that something is wired wrong? Describe your low voltage wiring and how it connects to the button(s), the chime, and the transformer
 
  #13  
Old 03-19-06, 08:40 AM
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I usually deal with transformer hum, by putting a rubber washer between the box its mounted in and the actual transformer, I then put a second one on top of the transformer before the screw mounts it to the box. This method usually cuts the hum by 100%.

-Roy
 
  #14  
Old 03-19-06, 08:53 AM
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If your chime requires a 30VA Xfmr, then that is too much current for a 15VA xfmr. It will tend to hum, and have a short life.
 
  #15  
Old 03-19-06, 12:36 PM
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Nothing to do with doorbells, but a Volt/Amp is a measure of reactive power which may or may not be the same as a watt depending on the nature of the load. In an AC cicrcuit the load may not be purely resistive. Reactive loads cause a current lead or lag. This lag/lead is computed as PF (power factor).
 
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