×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Transformer Wiring

Transformer Wiring

Transformer Wiring

(OP)
Is it possible to rewire a single phase isolation transformer to provide a 1:2 voltage output ratio.

RE: Transformer Wiring

YES.
That is if it is a type of transformer that may be rewound. If so,it may be rewound for a 2:1 ratio.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Transformer Wiring

(OP)
Yes I have access to the primary and secondary wires.  The transformer is small and only rated for 6A at 117V.

RE: Transformer Wiring

Do you mean rewind or reconnect? I mistakenly read your post as "rewind".
What are the ratings on the transformer?  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Transformer Wiring

(OP)
I was just typing as it came across.  I noticed you mentioned rewound, and I was thinking for rewire!  It is an isolation transformer, 117/117V, single phase, 6A, with a shield.  Looking to use it to get 220-240V to an outlet. Not a permanent installation, just a shop toy.

RE: Transformer Wiring

You may be able to use it as an autotransformer but it will no longer be isolated. In addition you may have 240 Volts to ground where a normal 240 Volt circuit has only 120 Volts to ground.
Connect one primary lead to one secondary lead. Connect this point to the grounded circuit conductor. (This will avoid 240 volts to ground if done properly.)
Energise the primary.
Check the voltage from the single primary lead to the single secondary lead. If the voltage is zero, reverse the two secondary leads. You should now have 240 volts.
BEWARE THE OUTPUT IS NO LONGER ISOLATED.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Transformer Wiring

waross nailed the answer I was going to post.

"Not a permanent installation, just a shop toy".

In the years I spent testing, troubleshooting and commissioning power systems, I often found myself having to 'lash up' equipment I had on hand to provide a function that my equipment did not support but that I needed.

Turning an isolation transformer into an autotransformer is a good example.  Just remember that when YOU do this, YOU know it's no longer an 'isolation transformer' but something entirely alien to whatever the nameplate might say. It is therefore dangerous to somebody who doesn't know about your modification.

This makes for a very unsafe condition, so be very careful about leaving such a useful little beast laying around for somebody else to work with.

old field guy

RE: Transformer Wiring

(OP)
I have a 3-Ph motor controller for 200-240V.  I only have 120V 1-Ph available.  In an effort to program the inverter prior to installation, the inverter is able to function with 240V across L1 and L3 terminals.  Not looking to connect motor yet, just preset the drive parameters.  

I had cut an extension cord, and rewired to the transformer primaries.  The green ground wire is connected to the shield cable of the transformer.  I connected an outlet in series with the secondary.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources