Nelson Pass has a unique idea of using a diode bridge on the safety ground. The diode drops will break up any ground loops and it will conduct if a fault exceeds a few volts or so.
Elegent.
Elegent.
An externally hosted image should be here but it was not working when we last tested it.
Hi frank2395,
We use a resistance to reduce circulating ground currents. A direct connection would tend to encourage this.
The currents we are concerned about can flow through the sheilds of the connecting audio cords and back through the chassis and ground pin on the power cord back to the offending equipment. Could even be as simple as a different phase of power off the breaker (fuse) panel.
These currents can become very high (destructive). I'd rather burn out a resistor rather than PCB traces. This may possibly destroy components. Close lightning strikes are my favorite example of this. There is no real protection against this.
-Chris
We use a resistance to reduce circulating ground currents. A direct connection would tend to encourage this.
The currents we are concerned about can flow through the sheilds of the connecting audio cords and back through the chassis and ground pin on the power cord back to the offending equipment. Could even be as simple as a different phase of power off the breaker (fuse) panel.
These currents can become very high (destructive). I'd rather burn out a resistor rather than PCB traces. This may possibly destroy components. Close lightning strikes are my favorite example of this. There is no real protection against this.
-Chris
ttray321 said:
No, for safety you must use two diodes back to back in parallel, and high current ones at that. A cheap convenient source of high current diodes is a 35A bridge rectifier...
Incidentally, I believe the diagram in the earlier post has an error in it; the lower AC terminal of the bridge rectifier should connect to the same point as the upper AC terminal (ie, the negative side of the upper DC supply).
Hi ttray321,
The capacitor is for RF frequencies. Depending on what is earthed and what is at circuit ground. The value will be different depending on who designed and built the object in question. Try different values as these are ballpark anyhow.
I normally earth the chassis for safety and RF shielding, hence the lack of C for me. Then there is no safety issue when the resistor burns out.
-Chris
The capacitor is for RF frequencies. Depending on what is earthed and what is at circuit ground. The value will be different depending on who designed and built the object in question. Try different values as these are ballpark anyhow.
I normally earth the chassis for safety and RF shielding, hence the lack of C for me. Then there is no safety issue when the resistor burns out.
-Chris
EC8010 said:
I truncated that diagragm, but maybe not enough. The only part that's really relavent is the bridge rectifier connected to the AC/Mains ground.
The bridge will not pass signal ground loop current ( no loop hum), but will conduct over a few volts and serve as a safety ground.
A 35A bridge rectifier is just fine.
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