Author Topic: What to look for in an isolation transformer.  (Read 2949 times)

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Offline perfect_disturbance

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What to look for in an isolation transformer.
« on: November 14, 2012, 05:54:54 pm »
I'm looking to build a system for switching on and off christmas light automatically.  Since this requires I work with wall voltage I figured I might implement some safety procautions in my work area rubber mat, and an isolation transformer to start.  I was looking at isolation transformers and wanted to know what people thought I should be looking for?

Here are a couple I found during a quick search on amazon:
http://www.amazon.com/Tripp-Lite-Isolation-Transformer-Outlet/dp/B00006HPFH/ref=sr_1_1?ie=UTF8&qid=1352915080&sr=8-1&keywords=isolation+transformer
http://www.amazon.com/Variac-Variable-Transformer-Isolation-1000va/dp/B006NGC6HU/ref=sr_1_8?ie=UTF8&qid=1352915080&sr=8-8&keywords=isolation+transformer

I want to get started on my real project so I don't want looking for/building one of these a project of it's own.
 

Offline Zero999

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Re: What to look for in an isolation transformer.
« Reply #1 on: November 14, 2012, 08:45:46 pm »
The variac looks good.
 

Offline Kremmen

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Re: What to look for in an isolation transformer.
« Reply #2 on: November 14, 2012, 10:16:55 pm »
The variac sure looks good and very Xmassy in the red paintwork. But is it the right gadget for you, i don't know.
Almost by definition a variac is NOT isolating. Now this one says it is, but before buying it for that purpose, make real sure that it really is. The picture shows a unit that typically would not be. Another thing is that variable voltage is not a feature of an isolation transformer so are you sure that is what you are looking for?
To qualify as a proper isolation transformer there need to be specific construction details indicated by the safety transformer symbols. You can see them here in the Wikipedia picture below the CE mark http://en.wikipedia.org/wiki/File:Trenntransformator.jpg
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Offline Psi

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Re: What to look for in an isolation transformer.
« Reply #3 on: November 14, 2012, 10:24:18 pm »
Maybe post a question saying you will buy it, but if its not isolated like stated you will require a refund.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline IanB

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Re: What to look for in an isolation transformer.
« Reply #4 on: November 14, 2012, 10:31:16 pm »
I might suggest overall that it is better to learn how to work safely with electricity rather than to get a false sense of security from using an isolation transformer.

Some good working practices include:
- not touching the circuit while it is energized
- use a test probe with one hand only and keep the other hand behind your back
- use test probes with clips where possible so you can be hands-off when testing
- unplug the circuit before working on it and don't rely on a switch
- connect a lamp to the supply so that the light is always lit when the circuit is plugged in
- power the circuit from a GFCI outlet
I'm not an EE--what am I doing here?
 

Offline perfect_disturbance

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Re: What to look for in an isolation transformer.
« Reply #5 on: November 15, 2012, 12:09:14 am »
I agree that safety precautions like an isolation transformer are no replacement for good safety practices but as people aren't perfect least of all me. I'd like to have taken whatever precautions are prudent.
 

Offline IanB

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Re: What to look for in an isolation transformer.
« Reply #6 on: November 15, 2012, 12:34:09 am »
Fair enough, but make sure you consider the circuit to be just as dangerous with an isolation transformer as without one. 120 V is 120 V and a typical isolation transformer has more than enough current to electrocute you.
I'm not an EE--what am I doing here?
 

Offline Zero999

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Re: What to look for in an isolation transformer.
« Reply #7 on: November 15, 2012, 10:51:59 am »
The variac sure looks good and very Xmassy in the red paintwork. But is it the right gadget for you, i don't know.
Almost by definition a variac is NOT isolating.
It says in the spec' it's an isolating variac.

It's actually quite easy to make an isolating variac buy making a toroidal isolation transformer with the primary on the inside and secondary on the outside with the enamel filled off and the usual carbon brush assembly.

the only question I have is whether there's a requirement to go up to 230V for testing European equipment? It might be handy to test a universal SMPs over the full 0 to 250V range.
 


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