Author Topic: Isolation transformer floating?  (Read 2895 times)

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Offline horleTopic starter

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Isolation transformer floating?
« on: June 09, 2016, 09:45:56 pm »
Hey guys!

I got myself an isolation transformer off ebay. Toroid ISB - 100W
https://toroid.com/Transformer-Products/IsoBox-Transformers/International-W-Series

I just wanted someone more experienced to confirm my thoughts.

I'm a bit confused about the odd number of wires. It has 2 primaries and 2 secondary windings. That's 4 wires in, 4 wires out. But there is a 9th green wire that is hooked up to protective earth that I can't find in the transformers datasheet. https://toroid.com/Portals/0/pdf/isolation_transformers/798.1202.pdf
It is neither connected to the secondary nor the primary windings.
I read about isolation transformers which have the secondary bound to ground but that is not the case here.

While I measure some AC voltage 180 and 40V between the output pins and mains earth there is no significant current (checked with a light bulb). So I assume that's just some stray voltage.

So what is the 9th wire good for? Grounded core?

And why are the output sockets protective earth pins connected to mains protective earth and chassis? what sense does that make if the power supply is floating?

Due to my measurements my output should be floating right? I'm just confused because I read somewhere that medical isolation transformers are earth referenced while "technical" isolation transformers are not. So you have to mod them. But I don't see what I should mod here...

Cheers!

« Last Edit: June 09, 2016, 09:49:50 pm by horle »
 

Offline retrolefty

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Re: Isolation transformer floating?
« Reply #1 on: June 09, 2016, 11:59:28 pm »
Quote
So what is the 9th wire good for? Grounded core?

 It's wired to a full copper shield that helps cut down capacitance coupling of noise between primary and secondary windings and should be connected to ground. It's a extra cost item that better isolation transformers have. Very common on instrumentation grade equipment.
 


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