Isolation Transformer

Discussion in 'General Electronics Chat' started by AutoNub, Feb 27, 2012.

  1. AutoNub

    Thread Starter Member

    Oct 14, 2011
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    Wikipedia says isolation transformers are 1:1...

    However, doing a search for step up or step down isolation transformers produces results (example here). How can an isolation transformer be a step up or step down transformer when the turns ratio is 1:1? 1:1 means what you get in is what you get out, right? What am I missing?
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    All transformers are in effect "isolation" transformers. They provide galvanic isolation from the 'mains' voltage. The term "isolation transformer" has come from the use of supplying the 'mains' voltage WITH isolation from that mains circuit. To do that the ratio of primary to secondary is 1:1.

    With the isolation 'ground is taken out of the circuit, you can be grounded and touch ONE of the secondary wires and not get shocked/killed(still not suggested to do this). BUT you can NOT touch both secondary wires.

    The main use of "isolation" transformers is in medical equipment, but is used in other equipment too.
     
  3. AutoNub

    Thread Starter Member

    Oct 14, 2011
    44
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    Thanks for the reply but I don't think it answered my question. Everything I've read about isolation transformers suggests that it must have a 1:1 turns ratio. This makes sense, but then why does it appear one can buy Isolation step up or step down transformers (see the link I provided in my previous post)?
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Most isolation transformers (those used specifically for isolation) are 1:1 but there's no reason they can't have other ratios. Isolation has nothing directly to do with the turns ratio. For example, the link you provided shows 1:1 and 2:1 (if you need to operate 120V equipment from a 240V line) isolation transformers.

    As shortbus noted standard power transformers all provide isolation but there is an exception for auto-transformers such as Variacs. They only have one winding and thus the input and output share a common connection.
     
  5. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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  6. #12

    Expert

    Nov 30, 2010
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    Dear AutoNub, What you are picking at is word usage.
    Try this on:

    Once upon a time, transformers were invented. Their early use was prolific in radios. Even Mr. Marconi had one. They came in all kinds of impedances and ratios. They were all called transformers.

    There were also some transformers that did not provide galvanic isolation. It is cheaper to leave out the secondary winding and just put taps on the primary winding :) They were called "autotransformers" to make sure nobody forgot the lack of a safety feature common to almost all transformers. This led directly to the invention of the opposite of an auto transformer. Instead of transforming voltage and current with no isolation, it would transform neither, but provide isolation. This was called an "isolation transformer"!

    Fast forward 100 years and we now have salesmen calling a 2:1 transformer an "isolation transformer". The nerve of him! Salesmen can't just twist words like that!
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    If we just called it an "isolation winding do-hickey" we could avoid all the confusion :)
     
  8. crutschow

    Expert

    Mar 14, 2008
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    Some transformers specifically designed for isolation have capacitance shields to minimize capacitive coupling between the input and output. And the input and output windings are wound on isolated plastic bobbins to insure there is little possibility of an accidental short occurring between the two windings since the two never come in physical contact. Typical uses are for high isolation test and medical equipment requirements.
     
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