You can estimate the power rating by how big the core area is or by the weight of the core as well.
http://www.diyaudio.com/forums/powe...rating-iron-core-transformer.html#post3551287
http://www.diyaudio.com/forums/tubes-valves/196839-output-transformer-power-rating.html#post2715049
This link has a graph chart that you can use that goes by core area in mm^2,
Determining Ratings of used surplus transformers
jer
http://www.diyaudio.com/forums/powe...rating-iron-core-transformer.html#post3551287
http://www.diyaudio.com/forums/tubes-valves/196839-output-transformer-power-rating.html#post2715049
This link has a graph chart that you can use that goes by core area in mm^2,
Determining Ratings of used surplus transformers
jer
I am aware of two quite different methods of specifying transformer VA.
If the transformer and the specification is unknown then we can never know which of these two methods has been applied.
Method 1.
specify the VA to reach a specified maximum operating temperature.
Method 2.
specify the VA to reach a specified transformer regulation.
There may be other ways to specify VA.
I am very inclined to agree with Gmp
If the transformer and the specification is unknown then we can never know which of these two methods has been applied.
Method 1.
specify the VA to reach a specified maximum operating temperature.
Method 2.
specify the VA to reach a specified transformer regulation.
There may be other ways to specify VA.
I am very inclined to agree with Gmp
if you can do an open circuit test and a short circuit test and then add the two powers together taking into consideration that small traffos have efficiencies in the 90% range, then you will have a ballpark rating...
the other consideration is temp rise, how hot are you willing to operate your traffo....
you will need test equipment like a wattmeter, a variac, an ac ammeter and ac voltmeter...Short circuit test - Wikipedia, the free encyclopedia
Open circuit test - Wikipedia, the free encyclopedia
yes, do not do this test if you do not have the proper equipment and knowhow...
How do you know the short circuit current.
I cannot see a method of determining the short circuit current in that test set up.
the picture is self explanatory...http://en.wikipedia.org/wiki/Short_circuit_test
this is a test result...http://www.antekinc.com/pdf/AN-104115.pdf
you can connect the dots to give you the idea...
short circuit tests lets you apply the rated primary current without burning out your traffo...
if you do not know rated primary current, you can make engineering guesses, that is why i say,
if you have not done this before be very careful...
this is a test result...http://www.antekinc.com/pdf/AN-104115.pdf
you can connect the dots to give you the idea...
short circuit tests lets you apply the rated primary current without burning out your traffo...
if you do not know rated primary current, you can make engineering guesses, that is why i say,
if you have not done this before be very careful...
andrew, i suggest you read up more on that topic...get yourself some electrical engineering books for more information...
you will see that you need not ask these questions...
The ARRL Handbook recommends this procedure:
"The current rating of the [secondary] windings can be determined by loading each winding with the primary connected directly to the ac line. Using power resistors, increase loading on each winding until its voltage drops by about 10% from the no-load figure. The current drawn by the resistors is the approximate winding load-current rating."
"The current rating of the [secondary] windings can be determined by loading each winding with the primary connected directly to the ac line. Using power resistors, increase loading on each winding until its voltage drops by about 10% from the no-load figure. The current drawn by the resistors is the approximate winding load-current rating."
I read that in my ARRL and immediately discarded the method as "completely flawed".
eg.
suppose you have a 23% regulation transformer with 4 equal secondaries.
Load all four windings until all 4 drop by 10%. Are you near the VA rating of the transformer?
Next load just one secondary until it drops by 10%. Are you near the VA rating of that winding, or near the VA rating of the transformer?
Now try the method on a 3.5% regulation two secondary transformer.
Load one winding to the -10% voltage, load both windings to the -10%.
You have two results. Are either of them close to the VA rating of the winding, or to the VA rating of the transformer?
Someone who is unfamiliar with transformer VA ratings and how to estimate them will be lost with any of these results. He/she will have no idea whether they have arrived at a good estimate. All they have is the ARRL method to rely on and I claim it is NOT a useful guide.
BTW, one of the results in the above examples is getting close to the VA rating and would be a good first guess at the VA rating. Any ideas on which one?
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