RE: buzz buzz buzz - I wonder why it does?

["Keith Doxey" <lists.diyha@xxxxxxx>]

Explanation time - excuse the poor ASCII graphics

 

Auto Transformer

 

A transformer with a single winding that has a tapping to obtain a different voltage from the input. Does not provide electrical isolation as the output has a direct connection to the input

 

L IN -------------------*

                          *

                          *

240V                  *------------------------- L out

                          *

                          *                         120V

                          *

N IN -------------------*------------------------N Out

 

 

A conventional transformer has two physically separate winding and provided isolation

 

L IN -------------------*

                          *

                          *    *--------------- L out

240V                  *     *

                          *    *          120V

                          *    *                  

                          *    *----------------N Out

N IN -------------------*

 

A site transformer is an isolation transformer designed for use on a building SITE (guess where the name comes from!)

Because of the often wet environment the output is centre tapped and tied to ground. This limits the maximum voltage to earth to half of the output voltage. Most shocks are from a single conductor to earth so this is an extra safety feature

 

 

L IN -------------------*

                          *

                          *    *--------------- L out --------- 55V L to earth

240V                  *     *

                          *    *------- Earth              110V across L and N

                          *    *                  

                          *    *----------------N Out-----------  55v N to earth

N IN -------------------*

 

THe HUM comes from the rattling of the transformer core laminations moving in the magnetic field of the transformer. All transformers will hum to some extent but it depends on the quality. Some have laminations held together by a weld across the centre, others are bolted together and the bolts can sometimes be tightened slightly to reduce the humming

 

A site transformer is probably not as tightly laminated as a transformer designed for equipment used in an office/home. I doubt you would hear the hum over the sound of a dumper truck or cement mixer :-)

Keith

www.diyha.co.uk
www.kat5.tv

-----Original Message-----
From: BUTLER, Tony, FM [mailto:tony.butler@xxxxxxx]
Sent: 18 April 2002 08:50
To: 'ukha_d@xxxxxxx'
Subject: RE: [ukha_d] buzz buzz buzz - I wonder why it does?

> http://www.screwfix.com/product.phtml?6158
>
> 53.42 for a 3kVA model

Well, I bought one of these puppies - bloody heavy they are too :( (and
BIG!)
Not got my stip block from Li yet so can't test the amp, but......
I plugged it in anyway for a laugh and IT BUZZES!!!!
Okay, technically, it hums, but it's a LOUD hum and, assuming the shelf in
my cupboard could stand the weight, I'm pretty sure the noise level would be
way too high on the SWMBO scale.
Why do these bloody things make noise then?
Maybe this is the difference between auto xformers and manual (for want of a
better word) xformers? :}

Damn blast and bugger is all I can say :(


Tony


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