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Re: transformers in series



Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Justin,

My first guess is that the secondary coils are floating and what ever voltage difference you measured is due to stray capacitance.

Gerry R.


Original poster: Justin <rocketfuel@xxxxxxxxxxxxx>


Today I played with my 2 new potential transformers (60:1 ratio for 120V/7500V)
and I measured something which has me stumped.

With the two transformers not connected to eachother, I reduced the voltage
to 1V with my variac and measured 60V on each secondary, which I expected.
However, When I started measuring voltages between the two transformers,
I got values I wasn't expecting.  For example, if transformer A has HV
terminals labelled 1 and 2, and transformer B has terminals 3 and 4, this
is what I found:

1-2: 60VAC
3-4: 60VAC
2-4: 1VAC
1-3: 1VAC
2-3: 20VAC
1-4: 20VAC

Now the 1VAC I was seeing between 2-4 and 1-3 I understand, but why 20V
between 2-3 and 1-4?  I was expecting 120V, although I know from reading
about other people's configurations that 1-3 or 2-4 are typically
connected, and indeed connecting them together did produce 120V on the
non-connected terminals.

What I don't understand is why I got the 20VAC reading when they were
not connected together!


Any help in explaining the fundamentals here would be greatly
appreciated.


Thanks!

Justin