I've been reading about the fact that a bit of DC on the mains can cause toroidal transformers to hum more than normal. So I decided to try to measure it I've got no toroidal transformers I'm just interested to try to measure it. Any how I ran a 150 watt bulb via a half way rectifier and got around 480 millivolts DC from neutral to earth and around 10 millivolts live to earth and live to neutral I then reversed the diode but still the voltage was only from neutral to earth why would this be? Incidentally with the diode the other way round the earth was 480 millivolts POSITIVE to neutral. The way I measured it was with my best quality meter ( the true RMS 6000 count one) switched to DC Volts range. My other meters couldn't make sense of anything when connected to the test terminals on DC range with AC mains present. Why could I only measure the offset on the neutral side? Surely it shoul be present on both sides.
Hello, Is the diode on the Neutral side of the lamp? When a diode conducts there is a small voltage drop across it. In the case of a silicon diode about 0.6V (varies with temperature). I think you are just measuring this voltage drop that's why it reverses when you reverse the diode. When to measure L-N you will get the same reading with or without the diode in circuit unless there is a lot of upstream impedance. Its asking too much to expect even a good meter to find mv of DC in 230V+ of noisy ac.
You would need some form of active low pass filter with a very low cut off frequency. Google will produce some designs.
Hello, Is the diode on the Neutral side of the lamp? When a diode conducts there is a small voltage drop across it. In the case of a silicon diode about 0.6V (varies with temperature). I think you are just measuring this voltage drop that's why it reverses when you reverse the diode. When to measure L-N you will get the same reading with or without the diode in circuit unless there is a lot of upstream impedance. Its asking too much to expect even a good meter to find mv of DC in 230V+ of noisy ac.
You would need some form of active low pass filter with a very low cut off frequency. Google will produce some designs.
