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Products => Test Equipment => Topic started by: radiogeek97 on March 22, 2013, 05:05:55 am

Title: variac transformer question
Post by: radiogeek97 on March 22, 2013, 05:05:55 am

i was wondering could a variac transformer function function as an effective isolation transformer.  i wanted to mains isolate some devices before i test them with my scope i dont have an isolation transformer bout have access to a variac.   
thanks
john

Title: Re: variac transformer question
Post by: Psi on March 22, 2013, 05:09:22 am

no, variacs provide no isolation.

Here's a diagram of the wiring
As you can see, the input and output are connected.
(https://www.eevblog.com/forum/testgear/variac-transformer-question/?action=dlattach;attach=42048)

Title: Re: variac transformer question
Post by: digsys on March 22, 2013, 05:10:07 am

Absolutely NOT !! A Variac has one side Referenced t the output ie it's an auto-transformer.
Sorry, you'll need an isolation transformer.

Title: Re: variac transformer question
Post by: grenert on March 22, 2013, 05:17:52 am

There are a very few variacs which have isolation, but nearly all variacs DO NOT have isolation.  So, most likely your variac will not be isolated.
One model which has both variable AC and isolation is the BK Precision 1653A:
http://www.bkprecision.com/products/power-supplies/1653A-150v-2a-ac-power-supply.html (http://www.bkprecision.com/products/power-supplies/1653A-150v-2a-ac-power-supply.html)

Another is the Global Specialties 1505:
http://www.alliedelec.com/search/productdetail.aspx?sku=70156612 (http://www.alliedelec.com/search/productdetail.aspx?sku=70156612)

Title: Re: variac transformer question
Post by: radiogeek97 on March 22, 2013, 10:33:49 am

thanks fellas i appreciate the help.  i am sure the variac my neighbor has is not the one of the very few that provides isolation.  I guess i will check ebay for a resonable isolation  xformer.

thank you all !