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. If
it doesn't get too hot on short circuit, the copper losses aren't too high.
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.
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....
73
Peter SM/G3RZP/P
========================================
Message Received: Aug 10 2005, 11:18 PM
From: "David Kirkby"
To: g3rzp@g3rzp.wanadoo.co.uk
Cc: StephenTetorka@cs.com, "amps@contesting.com"
Subject: Re: Testing filament xfmr
Peter Chadwick wrote:
> Simpler is to connect an ammeter across the secondary, feed the
> primary from a Variac and wind up the Variac until trhe desired filament
> current flows. then leave it for a time and see how hot it gets.
The classic short circuit test.
> The
> probability is that most of the losses will be copper losses:
agreed
> leave it
> on full primary with open circuit secondary to get an idea of how much
> iron loss there is by the temp rise.
It's a long time since I did this, but the short and open circuit tests
give you copper and iron losses respectively. I think you can show that
theoretically copper_loss == iron_loss for maximum efficiency, but the
transformer would no doubt have been wound on a suitable former, rather
than one that is theoretically optimal.
I can't really see how you could determine the temperature rise too
easily by this.
It's not my area of expertise, but I would have thought a load resistor
a safer bet.
--
David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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