transformer resistances

[amdx]

"davidt" <dav1d@talktalk.net> wrote in message
news:cc842a62-c98b-44de-a743-4e2b99a6c09c@o77g2000hsf.googlegroups.com...

I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?

You have it backwards. The high voltage side will have more turns
of smaller wire. (it carries less current) The low voltage side will have
less turns if thicker wire. (it carries more current)

 

[davidt]

I have an transformer from a old power supply.
It has 2 red wires and 2 yellow wires.
I think the red wires are the high voltage (mains) in and the yellow
the low voltage (12v ?) out,
To check this I touched a 6V battery across the yellow wires and got a
high voltage across the red wires (enought to spark across a 3mm gap)
But when I measure the resistance across the red wires I get 31.1ohms
and across the yellow 10.4ohms.
This is not what I expected.
I thought the high voltage winding would be thicker wire and less
turns than the low voltage winding and so would have a lower
resistance.
Could anyone explain where I am going wrong?