I want to measure mains voltage using a transformer. bought a 9V transformer, removed the secondary and rewind it with 10 turns that gives me 2mV per volt 1:500.
The problem is that the ratio is not constant, the ratio decreases from 1:530 to 1:470 as voltage increases on the primary (primary voltage range is 0-250VAC).
- Why is this change in ratio happening and how I can compensate for it?
Update: I tried winding 10 turn around the primary but problem still exists, I also decreased the load from 100Ω to 10KΩ.
Update2: When I wind another secondary around the primary, the first secondary was in place and I had two secondaries, I removed the first secondary and left with only one secondary winded around the primary. Now the ratio is much more stable, ranging from 1:470 to 1:490.