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Old 13th April 2012, 12:59 PM   #11
AndrewT is offline AndrewT  Scotland
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No.
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Old 13th April 2012, 01:01 PM   #12
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Of course it will.

If a transformer is rated at 4A then you can load it to 4A and make sure that it is running and not getting too hot. You can also expect the voltage to be within approximately 90% of its no load voltage.

If you need more precise regulation figures you are going to need its datasheet.
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Old 13th April 2012, 01:04 PM   #13
AndrewT is offline AndrewT  Scotland
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Still no.

I accept and recommend that a LOAD TEST is the best way to determine the VA rating of the unknown transformer.

But you must have the equipment and knowledge to allow the test to be carried out in a meaningful way. Otherwise the results will be worthless.
Worse, one incompetent Member is quite likely to damage a perfectly good transformer due to lack of resources.
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Old 13th April 2012, 01:06 PM   #14
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Originally Posted by AndrewT View Post
Still no.

I accept and recommend that a LOAD TEST is the best way to determine the VA rating of the unknown transformer.
So finally BLACK is BLACK and you do agree.

Hopefully the guy will have some common sense and apply the load gradually.

Maybe 0.5A at a time until the voltage starts to drop.
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Old 13th April 2012, 01:08 PM   #15
AndrewT is offline AndrewT  Scotland
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I never argued with your statement that a LOAD TEST is good.

What I abhor is your completely useless method, that you are recommending to an incompetent Member.
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Old 13th April 2012, 01:09 PM   #16
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It works.
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Old 13th April 2012, 01:11 PM   #17
AndrewT is offline AndrewT  Scotland
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I refer you back to post9.

Now try to compare post4 and post5 and try to convince us that your method is safer than mine.
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Old 13th April 2012, 01:12 PM   #18
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Quote:
Originally Posted by MrAdel1984 View Post
Hi Guys


I bought a 28 0 28 / 4 amp CT transformer to use it to build my first Gainclone
I suspect the seller has given me a lower than 4 amp trafo , so I wanted to test the amperage myself , the only way I found is to connect the trafo's secondary to an ATX ps 12v , I did this after I measured the seconary resistance which was 3 0 3 ohm, so 12/3=4 amp ,anyway I got only 2.5 dc amp running throug the secondary , the transformer gradually heats up and took about 25 min to be so hot that I can barely touch it , so can this trafo handle say, 3~4 amp ac current.

Thanks in Advance
you did the wrong thing putting on dc in your taffo windings, your finding 3ohm per side dc resistance on your traffo secondary is enough and paints a good picture of already.....

drawing 1 ampere out from your secondaries drops 3 volts per side, so that your 28-0-28 traffo becomes a 25-0-25 traffo.....

drawing 2 amps, your traffo secondary drops some more so that it now becomes a 22-0-22 traffo....

more current drawn means lower voltages.....this is called regulation...
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Old 13th April 2012, 01:13 PM   #19
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I'm not going to get into an argument.

It is ONE WAY of identifying the VA rating of a secondary.

If you have other ways then voice them and help this guy out.

Weighing it doesn't help much unless you know 1) The material and 2) The flux density used by that manufacturer.
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Old 13th April 2012, 01:17 PM   #20
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a 28 0 28v / 4 A traffo means that the terminal voltages are 28-0-28 when a load resistor drawing 4 amperes are connected to its terminals...

having said this, the open circuit of your traffo must be higher than 28-0-28 to meet the 4amp load spec....
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