[Amps] Testing filament xfmr

[David Kirkby]

Peter Chadwick wrote:
> David said:
> 
>  
> 
>  >I can't really see how you could determine the temperature rise too
>  >easily by this.
> 
> If it doesn't get too hot on open circuit, the iron losses aren't too 
> high. 

But then any transformer that gets too hot open circuit is suspect. I 
guess if you run the input voltage too low, or run it at 50 Hz when it 
is designed for 60Hz, then it might get too warm then.

> If it doesn't get too hot on short circuit, the copper losses 
> aren't too high.

But when you put it into a short circuit, you only have the copper 
losses, not the iron losses.

Each on their own might not be too much, but get them together and its a 
different story. That was what I thought was the point of the short 
circuit open circuit tests - one gave you the copper losses, the other 
the iron losses.

I have some recollection from when I did me EE degree, that for maximum 
efficiency,

copper loss == iron loss.

But the old brain cells have no doubt suffered a bit since then, and 
since I have never worked professionally with power transformers, I 
could well be wrong.

But personally, I'd sooner stick it on a load.

> Probability is that it won't get too hot in service. Rough and ready 
> tests; most transformers seem to get hotter under load, suggesting that 
> copper losses predominate.

No, I disagree. The fact transformers get hotter under load just proves 
there are copper losses. It does not prove they predominate.

> Time to worry is when the pitch or resin or whatever bubble 
> out.......messier is the oil filled xfmer where the pressure leads to an 
> oil leak....
-- 
David Kirkby,
G8WRB

Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/