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Old 1st February 2011, 06:26 AM   #1
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Default is transformer with primary and secondary = isolation?

hi guys

i am confuse about the term isolation transformer.

is transformer with primary winding and secondary winding is regarded as isolation transformer?

say normal audio transformer of 0v-15v on its secondary. is this consider as isolation transformer as well which is only output 15v instead of normal 110v or 220v?

or isolation transfomer is something else that not just primary and secondary winding

thanks
erwin
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Old 1st February 2011, 06:30 AM   #2
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The usual meaning of an isolation transformer is a 1:1 ratio to supply the same voltage as the primary such that there is no galvanic connection between the source and load.

And yes, all transformers isolate but aren't called isolation transformers.
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Old 1st February 2011, 06:36 AM   #3
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thanks bob for the confirmation. i am clear now.

erwin
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Old 1st February 2011, 10:58 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
for mains use, isolation transformers are tested to very high isolation voltages. I think 1500Vac for a few seconds.
I doubt an ordinary audio transformer would meet this safety standard. They normally only handle a few volts or at most a few tens of volts.

The output transformer of a valve/tube amplifier may be safety tested to a similar standard as a mains isolation transformer.
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Old 1st February 2011, 12:11 PM   #5
Mooly is offline Mooly  United Kingdom
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Just to add that "auto transformers" and Variacs provide no isolation between input and output yet come in the category "transformers".
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Old 1st February 2011, 12:30 PM   #6
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A further clarification....True isolation transformers have whats called a split bobbin. The bobbin is the plastic core onto which the primaries and secondaries are wound onto. The "standard" bobbin has both primaries AND secondaries wound on top of each other in an interleaving pattern. The isolating value being the 'tape' that separates each stack of windings. The split bobbin has a large ( 3 mm?) wall of plastic, a barrier that separates both windings. The split bobbin is less efficient but has superior isolating properties.


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