Isolation transformers - buzzing

I just picked up a couple of 1KW isolation transformers. They're mounted in a thick steel box. I haven't looked inside yet to see whether they have any other kind of line conditioning, but I'm assuming not. When I plug them in, whether or not there is any load, they vibrate and buzz very loudly (for a transformer at least). Is there any way of getting rid of this ? maybe by adding an AC filter before it or something?

thanx
 

trwh

Member
2002-04-28 2:11 pm
UK
Hi schpeltor,

One of the main causes of transformers radiating mechanical noise is a small DC offset on the mains. This can be removed by AC coupling the mains input - there was a thread discussing this and someone posted a schematic for a suitable filter.

I've used AC coupling to quieten down a cheap EI transformer in a CD player before, but I'm not sure if it would still be practical for a 1kVA unit.

Anyway, 's food for thought,
Tim.
 

MRehorst

Member
2002-05-17 8:48 pm
Are they isolation transformers or are they line voltage regulators/conditioners?

Ferroresonant line "conditioners" all buzz and run warm even with no load. If you look inside and see large capacitor(s), they are ferroresonant. There is no way to make them quieter except to unplug them.

MR
 
schpeltor said:
In addition to filtering the mains input, what about potting it in some substance? I found recommendations for epoxy and shellac while searching the forum, what would be the best compound to completely encase the transformer with?

Search Compagnies that make epoxy, I've seen one (sorry son't remember the name) that made speacial epoxy for potting.
 

MRehorst

Member
2002-05-17 8:48 pm
If you pot the thing, you have to worry about heat build-up, and there's no guarantee you'll get the goop into the small spaces where it needs to get in order to be effective.

I restore "antique" radios and one of the old timer's tricks for fixing a buzzing transformer is to whack it on one of the corners with a wood or rubber mallet. In the case of a large transformer, you might need a wood or rubber sledge hammer...

MR