Re: Where to I put a Fuse ??

From: John Fields (jfields_at_austininstruments.com)
Date: 02/04/05 

Date: Fri, 04 Feb 2005 12:23:40 -0600

On Fri, 4 Feb 2005 12:23:58 -0600, "Trudeau" <Trudeau@123.com> wrote:

>
>"John Fields" <jfields@austininstruments.com> wrote in message
>news:i25701t8rfm5qn4sonfnioeav1h2ditn45@4ax.com...
>> On Fri, 4 Feb 2005 09:25:45 -0600, "Trudeau" <Trudeau@123.com> wrote:
>>
>>
>> >Thnaks again for your suggestions.
>> > Could someone explain, ( Simple as you can ) what the advantage of an
>> >isolation transformer would be in this project. As I understand it
>basically
>> >you have a transformer that separates the 120 house into I suppose 120
>> >coming from the other half of the transformer. (Is this called a 1 to 1).
>Im
>> >not sure what the difference is. Unless as I come to think of it you are
>> >reducing the amps from 15 house to say 1 or 2. I suppose this would have
>> >some added safety.
>> >Please Carify.
>>
>> ---
>> The reason for the isolation transformer is to place a galvanic
>> barrier between whatever's plugged into the output of the transformer
>> and the mains. That way, the likelihood that you'll kill yourself or
>> the equipment you're working on/with will be made somewhat smaller.
>>
>> --
>> John Fields
>
>Thanks for that.
>
>I'm a little unclear on what the Galvanic barrier does.
>
> I ve done a little research and learned that a galvanic process is a
>process that creates electricity. eg electricity in frogs legs.
> Secondly I have always know that when you put certain metals together that
>you get corrosion. I have now learned the name for this is a Galvanic
>Process.
>As far as the discussion at hand I have found that a Galvanic Barrier in a
>transformer :
>
>A. Galvanic barrier has no metal metal contact, Well Yes of course its a
>transformer. It uses fields to pass the current and air as the barrier. 

---
Well, only partly.  The insulation on the magnet wire and the nylon
walls of the bobbin separating the primary and secondary (if the
transformer is wound that way) do the galvanic isolation.
---
 
>I guess that not being directly connected to the mains is good. But its still
>120volts.
>B. A Galvanic barrier cuts down on noise. Not sure its important in this
>case.
>C. That a G.B. prevents ground loops. This I can see as being important.
>
>Am I right here. Are there more reasons to use the isolation transformer?
>I guess my confusion is that if the voltage coming into the transformer is
>the same coming out accept for the fact that it is cleaner and perhaps
>exactly 120 Volts. Im not sure what more added safety it adds, accept for
>the things I noted above. Sorry to be dense. What am I missing?
---
If you're working with mains hot and neutral directly, without going
through a transformer and you get hot and neutral reversed, the
chassis of what you're working on could be connected to mains hot with
the embarrassing result that you could fry a scope probe as soon as
you clip the probe's ground to chassis or to whatever you thought was
ground in the circuit.  Worse, you could be holding on to the chassis
when you grab the alligator clip...  Interpose an isolation
transformer between the DUT (device under test) and the mains and
those problems go away.  Of course you'll still have 120V coming out
of the transformer, but if you don't know enough not to grab ahold of
that, you'll probably be a candidate for a Darwin award soon,
anyway!^)
     
-- 
John Fields

Relevant Pages

  • Re: Isolation transformer
    ... electrically connected to the mains is a moot point. ... transformer is a 1:1 power transformer which is used as a safety ... isolation transformer, the bonding is eliminated, and the shock hazard ... expected "electrical connection to ground". ...
    (sci.electronics.basics)
  • Re: Any technical reason not to use isolation transformer to make DC?
    ... shouldn't use an isolation transformer to feed a rectifier & filter? ... As opposed to a purpose-designed 120VAC secondary "power transformer"? ... If this connects to mains you should use one unless the application is totally encapsulated and on its own. ... it pertains to using an isolation versus a rectifier transformer. ...
    (sci.electronics.design)
  • Re: Building an isolation transformer
    ... > I would like an isolation transformer for the UK mains. ... > to find any off the shelf designs though. ...
    (sci.electronics.basics)
  • Re: EN60065 - safety and audio in/out terminals
    ... I'm working developing an audio equipments that must comply with the ... EN/IEC60065 safety requirements. ... parts and the mains line terminals. ... You will probably have a transformer inside the cabinet. ...
    (sci.electronics.design)
  • Re: 2 phase AC to DC supply
    ... running the other transformer primary in series ... You don't need to do that, the rectifier circuits do it for you. ... the pulses of the phase-shifted rectifier would be in the ... that's with 125VAC input on the mains, ...
    (rec.radio.amateur.homebrew)
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