NP nails it. It’s a little unusual to have DC on the AC line but it does happen, and as he points out, it happens from a device that draws current only when the voltage is going one direction, but not the other.
Dimmers, but also some digital power supplies may cause this. Any oscilloscope will show this problem, Usually you won’t just see a shift int he AC signal, but you’ll also see some nasty noise along with it.
The traditional fix is an isolation transformer, which are usually not toroids and present an AC at the output with little or no DC. DC may occur in cheap isolation transformers as a result of uneven winding if they are center tapped at the secondaries. One approach that is sometimes cheapest is to put the offending device itself on an isolation transformer.
Other fixes are to move to another circuit, or especially to a circuit that’s on a different phase than the one causing the problem. More expensive solutions MIGHT be to improve the wiring to the service transformer, allowing the device (dimmer) that is causing the problem to draw more current without a voltage sag. If the house is old, uses fuses, etc. it's not a surprising thing to have, there may be other reasons to seek a wiring upgrade from a qualified professional.
Best,
Erik
Dimmers, but also some digital power supplies may cause this. Any oscilloscope will show this problem, Usually you won’t just see a shift int he AC signal, but you’ll also see some nasty noise along with it.
The traditional fix is an isolation transformer, which are usually not toroids and present an AC at the output with little or no DC. DC may occur in cheap isolation transformers as a result of uneven winding if they are center tapped at the secondaries. One approach that is sometimes cheapest is to put the offending device itself on an isolation transformer.
Other fixes are to move to another circuit, or especially to a circuit that’s on a different phase than the one causing the problem. More expensive solutions MIGHT be to improve the wiring to the service transformer, allowing the device (dimmer) that is causing the problem to draw more current without a voltage sag. If the house is old, uses fuses, etc. it's not a surprising thing to have, there may be other reasons to seek a wiring upgrade from a qualified professional.
Best,
Erik