# Crosstalk between secondary transformer windings

I have hand wound a transformer which has a 220v primary winding, two 25v secondaries and a 15v secondary: simulate this circuit – Schematic created using CircuitLab

I have centre tapped the 15v secondaries (to later rectify to +-25v) and when measuring the voltage between A-B or B-C, I get 25v as I would expect. Similarly between D-E I get 15v.

However, If I measure the voltage between B-D I get 5v, and B-E gives 15V.

A-D is also at 24v and A-E at 34v. I would have expected these to all be ~0v.

Why am I getting these voltages? I would have assumed that the 15v winding would be isolated from the 25v centre-tapped winding? I have checked there are no shorts between any the secondaries. I should also point out that this is under no load.

As I said I hand wound this transformer (well the secondaries), so is this something to do with the direction of the windings? Or unbalanced windings? I would like the 15v winding to be isolated from the 25v ones. Is this not possible with a shared core?

• Maybe capacitive coupling. What is the resistance you measure between the windings? Dec 24, 2013 at 16:16
• about 3ohm A-C and 2.2 D-E. 25v winding also has a larger wire diameter than the 15v. Meter OL's between the 25 and 15v windings (so no shorts) Dec 24, 2013 at 16:22
• I mean the resistance between A-D or A-E, ... Dec 24, 2013 at 16:23
• Infinite. Well the meter shows OL so I guess at least 100Mohm (dont know the specs of the meter) Dec 24, 2013 at 16:26
• What happens when you load the A-D, A-E, ... voltage with a 1k or 10k resistor? Dec 24, 2013 at 16:27