Hi,
I'm trying to find EMI schematic or board that does not require ground/earth pin. One of the house I visited often has old power wiring which do not have ground/earth (only two-prong wall sockets). We use RCCB (Residual current circuit breaker) for safety measure. Main AC line here is 220V, but can go high as 230-240V when measured.
However, there is EMI when large appliance, such as, water heater, refrigerator, turns on. It sent interference to preamp, which sound like loud high frequency pitch/hiss. I have purchased commercial EMI IEC socket but realized that they rely on ground/ earth to let the interference go.
I can't find solution but there are some articles on this but cannot find any proven schematics. Any thought?
AP
I'm trying to find EMI schematic or board that does not require ground/earth pin. One of the house I visited often has old power wiring which do not have ground/earth (only two-prong wall sockets). We use RCCB (Residual current circuit breaker) for safety measure. Main AC line here is 220V, but can go high as 230-240V when measured.
However, there is EMI when large appliance, such as, water heater, refrigerator, turns on. It sent interference to preamp, which sound like loud high frequency pitch/hiss. I have purchased commercial EMI IEC socket but realized that they rely on ground/ earth to let the interference go.
I can't find solution but there are some articles on this but cannot find any proven schematics. Any thought?
AP
Have you tried it?
Filtering across the 2-pin line will give some benefit, even if not as much as 3-pin filtering. Results will be very dependent on situation. How much spike the refrigerator makes, how well the 2-wire line absorbs it. And even without connecting to a large ground, just connecting a filter to the case of the amplifier is some help.
Clean and stable mains voltage and safety seem challenges where you are. In such areas often not many want or like to improve matters which makes the circle round.
Only good solution is to improve ones own home (you can’t change anything else) so with new solid 2.5mm2 wiring laid in PVC tubes, find PE (when RCCB are used PE will likely be there as well) and use it, install quality PE wall sockets and quality lighting switches etc. If screens go dark when switching on lighting it would be wise to find out why. Probably too thin wiring and bad connections and if so also possibly a fire hazard.
A 240V rated isolation transformer with a few output taps (220/230V) seems a worthwhile investment. These filter out noise and combined with a mains filter even more so. Overvoltage protection can be included. A bonus would be to be able to correct too high mains voltage. It is also probably wise to check if equipment has 240V primaries on the power transformers.
Only good solution is to improve ones own home (you can’t change anything else) so with new solid 2.5mm2 wiring laid in PVC tubes, find PE (when RCCB are used PE will likely be there as well) and use it, install quality PE wall sockets and quality lighting switches etc. If screens go dark when switching on lighting it would be wise to find out why. Probably too thin wiring and bad connections and if so also possibly a fire hazard.
A 240V rated isolation transformer with a few output taps (220/230V) seems a worthwhile investment. These filter out noise and combined with a mains filter even more so. Overvoltage protection can be included. A bonus would be to be able to correct too high mains voltage. It is also probably wise to check if equipment has 240V primaries on the power transformers.
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In theory, refrigerator and air conditioner turn-on pops are easy to reduce. But in practice it's a big challenge. A resistor/capacitor snubber (designed for the task) placed across the appliance's turn-on switch/relay will do the job. But the challenge is getting inside the appliance to that switch.relay.
The ground connection on filters is used to connect the Y capacitors. These caps are used to reduce the CM interferences of the device they are part of, mostly to meet the EMC regulations. They do little to protect the device from incoming noise, because the earth wiring is often as polluted as the mains, as it uses a common cable conduit.
In fact, the earth can be more polluted than the mains itself, precisely because it serves as a sewer to the numerous filters of class I devices it is connected to.
You can build a filter, and omit the Y caps when present. The filter will typically consist of one or more of CM chokes, to cover a wide frequency range, and a differential mode choke (or two single chokes) and X-rated capacitors.
In fact, the earth can be more polluted than the mains itself, precisely because it serves as a sewer to the numerous filters of class I devices it is connected to.
You can build a filter, and omit the Y caps when present. The filter will typically consist of one or more of CM chokes, to cover a wide frequency range, and a differential mode choke (or two single chokes) and X-rated capacitors.