transformer weirdness

taj · 19th May 2005, 07:47 PM

Hi, can one of you electronics whizes help me understand this...

I bought a 16VAC 40VA inline (like a laptop's) transformer and I can't figure out what's going on with the secondaries. Most of it seems normal to me. Here's my measurements on the 4 output wires:
e
White -> Red = 18v and .8 ohms DCR.
White -> blk = 9v and .4 ohms DCR
red -> blk = 9v and .4 ohms DCR

So far it looks like a normal 18 volt CT.

Green -> Red = 33v and infinte DCR
Green -> white = 18v and infinite DCR
Green -> red = 25v and infinite DCR

So how does this green (earth/ground wire) fit in? I don't understand where those voltages come from.

...TAJ

taj · 19th May 2005, 08:04 PM

I accidently deleted the sentence that said...

'the green wire shows 0-ohm DCR to the primary side earth/ground prong."

..TAJ

TwoSpoons · 19th May 2005, 09:58 PM

Let me guess ... you measured those voltages with a digital meter with a 10M ohm input impedance, right?

What you are seeing is capacitive coupling between pri and sec putting common mode volts between sec and ground. All perfectly normal.

taj · 20th May 2005, 02:28 AM

Well there yah go.

Thanks again.

19th May 2005, 07:47 PM	#1
taj diyAudio Member Join Date: Feb 2005	transformer weirdness Hi, can one of you electronics whizes help me understand this... I bought a 16VAC 40VA inline (like a laptop's) transformer and I can't figure out what's going on with the secondaries. Most of it seems normal to me. Here's my measurements on the 4 output wires: e White -> Red = 18v and .8 ohms DCR. White -> blk = 9v and .4 ohms DCR red -> blk = 9v and .4 ohms DCR So far it looks like a normal 18 volt CT. Green -> Red = 33v and infinte DCR Green -> white = 18v and infinite DCR Green -> red = 25v and infinite DCR So how does this green (earth/ground wire) fit in? I don't understand where those voltages come from. ...TAJ

19th May 2005, 08:04 PM	#2
taj diyAudio Member Join Date: Feb 2005	also I accidently deleted the sentence that said... 'the green wire shows 0-ohm DCR to the primary side earth/ground prong." ..TAJ

20th May 2005, 02:28 AM	#4
taj diyAudio Member Join Date: Feb 2005	Thanks! Well there yah go. Thanks again.

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19th May 2005, 09:58 PM	#3
TwoSpoons diyAudio Member Join Date: Oct 2004	Let me guess ... you measured those voltages with a digital meter with a 10M ohm input impedance, right? What you are seeing is capacitive coupling between pri and sec putting common mode volts between sec and ground. All perfectly normal.

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