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Old 13th April 2012, 02:20 PM   #21
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by KatieandDad View Post
.........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.
post4 lists useful information that will help to safely and non destructively determine if 4Aac is a reasonable value for rated output current.
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Old 14th April 2012, 12:54 PM   #22
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Hi guys

Sorry for late response and thanks for help
The trafo is -thank god- still alive and it's an E-I ,secondary wire diameter is about 0.5 mm, primary (couldn't see it)
Any Way , Trafo manufacturers in my country don't give a damn about amperage

Thanks
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Old 14th April 2012, 01:13 PM   #23
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As I keep saying.

Try giving a load.

Try about 0.5A at a time and see how it gets on, both in heat and voltage.

If the voltage starts to drop (more than say 10%) and/or it starts to get warmer than expected, then you have reached a sensible (max) load for that transformer.

If you want to be really delicate you can load it 100mA at a time but that is being overcautious.

The thickness of the Primary winding might be a "red herring" it is the thickness of the secondary winding that really determines the (max) output current.

0.5mm = 25SWG which is about 310mA. 250V x 0.31A = 80VA which is well outside what we are looking at. Obviously different manufacturers use different tables for maximum current but this is the norm. that I was taught in Colledge.

Last edited by KatieandDad; 14th April 2012 at 01:24 PM.
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Old 14th April 2012, 01:20 PM   #24
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Quote:
Originally Posted by KatieandDad View Post
As I keep saying.

Try giving a load.

Try about 0.5A at a time and see how it gets on, both in heat and voltage.

If the voltage starts to drop (more than say 10%) and/or it starts to get warmer than expected, then you have reached a sensible (max) load for that transformer.

If you want to be really delicate you can load it 100mA at a time but that is being overcautious.
Thank you KatieandDad.
I really appreciate your help
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Old 14th April 2012, 01:29 PM   #25
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There are loads of ways of home-building high-power shunts.

The two that come to mind are:

1) wire from an old electric fire element.

2) light bulbs.
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Old 14th April 2012, 01:37 PM   #26
AndrewT is offline AndrewT  Scotland
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Originally Posted by KatieandDad View Post
it is the thickness of the secondary winding that really determines the (max) output current.
it is the thickness of the primary winding that determines the maximum input current.
Both limiting values must not be exceeded for continuous operation.
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Old 14th April 2012, 01:39 PM   #27
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True,

But as you can see from the maths its proved meaningless.
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Old 14th April 2012, 01:47 PM   #28
AndrewT is offline AndrewT  Scotland
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It's your assumptions that are questionable.

0.5mm diameter gives ~0.2sqmm
At 3.1A/sqmm I would suggest that maximum primary current could be around 600mAac
For a 230Vac transformer that would predict a maximum input power of ~140VA and using 94% efficiency gives a maximum output power of ~132VA.

That to me is not meaningless.

Now apply the other data I suggested to see how they tally in predictions.
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Old 14th April 2012, 01:51 PM   #29
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Rather than waffle and argue, try helping this guy.
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Old 14th April 2012, 01:55 PM   #30
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Normal calculations are based on 1000A . square inch.

Some companies rely on the toroid to cool the wire as it is not enclosed. In the case of an EI construction we are at the mercy of the manufacturer.

A lot of them build in natural failure.
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