Discuss Failed RCD socket given post-mortem out of curiosity in the UK Electrical Forum area at ElectriciansForums.net
Amazing. I thought there was a little man inside, stood on a bucket, which he jumped off when the electric got too much.
Only a bloke would be daft enough to stand there for 32 years.Man/woman/gender neutral person surely.
(or should that be gender live & neutral?)
Oh Lucien. It was fully explained in post #11 you silly bean.When I first saw the board and before I read your comment, I took C1 to be the dropper, but a quick look at the tracks revealed that to be entirely R2, totalling 40k on the DC side of the bridge. So there's around 5mA available to power the amplifier at whatever voltage that zener is. One the one hand, a resistive dropper is wasteful. A 0.1μF cap could have saved something approaching a watt of dissipation and relative to the overall cost it's not a huge extra. But then, unless it was vastly overrated for voltage making it bigger and more expensive still, it would have suffered the same fate as most X-cap droppers, losing capacitance through repeated self-heal events and stopped the unit working after much less than 30 years.
The actuator coil seems to be powered separately by half-wave rectified AC (across one diode of the bridge) via that 47k (R3?), and flywheeled by D9. That scheme makes sense because it utilises the coil's inductance to reduce the resistor loss for a given average coil current, compared to feeding it from the bridge DC output. I can't see what actually trips it - is it shorted by the op-amp's output?
I was a bit surprised that it was mostly a resistive dropper, also a cap allows DC IR testing (in theory, depending on how the coil trips, etc)When I first saw the board and before I read your comment, I took C1 to be the dropper, but a quick look at the tracks revealed that to be entirely R2, totalling 40k on the DC side of the bridge. So there's around 5mA available to power the amplifier at whatever voltage that zener is. One the one hand, a resistive dropper is wasteful. A 0.1μF cap could have saved something approaching a watt of dissipation and relative to the overall cost it's not a huge extra. But then, unless it was vastly overrated for voltage making it bigger and more expensive still, it would have suffered the same fate as most X-cap droppers, losing capacitance through repeated self-heal events and stopped the unit working after much less than 30 years.
There seems to be CSR1 and CSR2 to the left of the coil and I think they are thyristors but not checked, I guess it has some ~340V charge on one of the other caps that is dumped in to the coil to trip the breaker. The thin wire and size makes it look unlikely it would go with the 10-20V of an op-amp output.The actuator coil seems to be powered separately by half-wave rectified AC (across one diode of the bridge) via that 47k (R3?), and flywheeled by D9. That scheme makes sense because it utilises the coil's inductance to reduce the resistor loss for a given average coil current, compared to feeding it from the bridge DC output. I can't see what actually trips it - is it shorted by the op-amp's output?
Oh Lucien. It was fully explained in post #11 you silly bean.
Amazing. I thought there was a little man inside, stood on a bucket, which he jumped off when the electric got too much.
It looks like one is used for the RCD trip but the other is li ked to earth so (I presume) if neutral is at an elevated voltage the socket is disconnected as well.I'm glad you pointed out the thyristors - I was expecting there to be one or two but I hadn't spotted them over in that corner, even though the silkscreen clearly shows CSR2*. It's hard to follow their connections behind the flying leads though.
No idea, but unexpected ordering of letters often suggests a French influence. I also remember that semiconductor diodes were often given the part number CR1, etc, as short for "crystal rectifier" so possibly some connection there?*Why is it that we speak (or used to speak) of SCRs, but the most common component designator was CSR?
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