Electronics > Beginners
Isolation transformer with a high voltage winding... how to handle it?
mlefe:
Hi guys, I'm working on a DIY isolation transformer to add to the bench (I got the transformer from a APC Line R 1200 voltage stabilizer ).
After a fair amount of analysis I was able to identify and separate all windings and choose the ones that I could use to have a primary and secondary.
The issue is that, from the way the transformer for the voltage stabilizer is built, if I put 110V on the primary, I can get 110V on the secondary just fine, but I also obtain in one set of windings more than 770V (7 times more than the voltage in the primary/secondary).
I think I can tape/insulate that pair of cables and leave them floating but I'm not really sure if that's safe (the whole thing will be in a box anyways) or if I have to take the "safest" path and completely dissassemble the transformer and remove the cables (and risk damaging the other windings and/or enamel of the core and then cope with the hum)
What do you think? What makes sense?
retrolefty:
Leaving unused secondary windings disconnected is fine, just dress them carefully with proper voltage rated tape or sleeving.
ArthurDent:
It sounds like what you're describing is a ferroresonant transformer that should only be used if the proper capacitor is wired across the other secondary winding. These transformers when properly wired generally produce a distorted sine wave output and a stronger external magnetic field than a conventional transformer although with the proper capacitor they will provide a stable voltage output.
http://www.electroncoil.com/ferroresonant_transformers.php
David Hess:
The APC Line-R 1200 uses a buck/boost autotransformer and not a ferroresonant transformer but I have no idea where a 700 volt AC winding fits with that. There should be a bunch of low voltage windings or taps.
I suspect it has a dual winding 120/240 volt primary so the same transformer can be used at 120 and 240 volts. The dual winding can be used as a 120 volt isolation transformer at the cost of increased copper losses so limit power to 600 watts continuous. Isolation will not be as good as with an isolation transformer which has physically separate primary and secondary and there will be no electrostatic screen between the windings.
ArthurDent:
The APC Line-R 1200 has a 3 position switch to set it for the line voltage in your area (110,120,127) but after you set it for your region, it is an automatic line regulator for 85-140 in a 120volt region. Here is a link to the manual that describes that.
http://www.apc.com/salestools/ASTE-6Z7V37/ASTE-6Z7V37_R1_EN.pdf
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