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Electronics => Beginners => Topic started by: Bzonic on October 12, 2016, 10:28:24 pm

Title: Isolation transformer @ 133 volts
Post by: Bzonic on October 12, 2016, 10:28:24 pm
Hello all,  I recently acquired this isolation transformer and have a question about the 1:1 theory of these.  Is it common for them to actually be putting out 130+ volts in a unloaded state?  I initially thought the thing was way out of spec but realized that maybe this is done on purpose to compensate for when a stiff load is connected.  After my initial multimeter reading of 132.5 in an unloaded state I then plugged in a Wagner heat gun and turned it on for a few seconds.  The 8 amp draw certainly made a difference and brought the reading down to 122v.  Is this considered completely normal with how Iso's are typically designed?  Any danger with using it for something that is a light load and thus likely to receive close to that 132 volts?  Thanks for any insight!

Brian
Title: Re: Isolation transformer @ 133 volts
Post by: Andy Watson on October 12, 2016, 10:57:13 pm
It is completely normal for a transformer. The output is specified under loaded conditions. When the load is removed the output voltage goes up - it's call regulation. Larger transformers usually have better regulation - i.e. less change - than small transformers.

Title: Re: Isolation transformer @ 133 volts
Post by: Zero999 on October 12, 2016, 11:18:04 pm
Yes, isolation transformers are normally wound for slightly more than 1:1 to compensate for the voltage drop when fully loaded.

You'll find that if you try to make your own isolation transformer from say two 120V:24V transformers connected back-to-back, the output voltage will be less than the input, when fully loaded.
Title: Re: Isolation transformer @ 133 volts
Post by: Bzonic on October 12, 2016, 11:26:19 pm
Thanks - makes perfect sense.  So using it on a light load with that 132V output should not be a problem?  I would think the answer would be "potentially".  It seems that a sensitive device might not handle the over voltage well?
Title: Re: Isolation transformer @ 133 volts
Post by: helius on October 12, 2016, 11:41:25 pm
It would be (just) within the +/- 10% specification that most devices are designed for. I wouldn't expect any issues.
Title: Re: Isolation transformer @ 133 volts
Post by: Bzonic on October 12, 2016, 11:56:04 pm
Thanks all!