Using 220v transformer with 110v mains

[DarpMalone]

I'll start by saying that I've only been messing around with this stuff for a few months, so I've got lots to learn. but I've been going crazy, building, modding and trying out every project I could get my hands on.

Last weekend I converted a plate amp, built for the UK so that I could use it in north america by replacing the 220v transformer with a 110v... Having an extra transformer laying around I decided to measure it's secondary from my 110 mains yielding a bit more than half the 220 voltage rating; 50VCT (perfect for a LM3886 chipamp that I'm working on). I tried it and it seems to work fine, but are there any safety issues here? If not, by doing this am I doubling the amperage rating to yield the same total VA rating?... (Ex a 220v, 180VA transformer with 93VCT @2A secondary is essentially the same as a 45VCT, 3.72A on a 110v mains)

Thanks

 

[Steerpike]

am I doubling the amperage rating to yield the same total VA rating?... (Ex a 220v, 180VA transformer with 93VCT @2A secondary is essentially the same as a 45VCT, 3.72A on a 110v mains)

The maximum current rating remains the same at 2A. So the VA rating is halved (=90).
It's safe to use it this way, but it's a waste of half of the transformers power rating.

 

[DarpMalone]

Thanks for your response

 

[multisync]

check to see if the primary winding has 2 coils, a lot of them do, if so you can parallel the primaries and then the power rating would be the same.

 

[sumaudioguy]

transformers by weight

It is handy to know the power ratings so similar or larger transformer can be used. Weight is a good measure of power so the weight of the transformer may be used to more or less decide the size to use. Of course EI core and toroid weight cannot be compared. EI core usually make about 35 watts per pound.

 

[DarpMalone]

Okay, but if I understand Steerpike correctly, a 220v transformer used on 110v mains would only have half the total VA rating that it's size would suggest (1/2 the total VA you'd achieve from 220v mains, since the voltage drops to half but the rated current stays the same)... This stinks cuz I purchased a nice 500VA, 220v transformer for next to nothing over the weekend

 

[Speedskater]

But, it will be a very robust 250VA! If you don't get carried away doing high power test tone tests, it will do lots of power when playing music.

 

[Steerpike]

Okay, but if I understand Steerpike correctly, a 220v transformer used on 110v mains would only have half the total VA rating that it's size would suggest(

That's exactly right.