Ac filters

[jleaman]

Originally posted by metalman
Jason,

If you want to do it right, start with one of THESE , and add the Jon Rirsch filter suggested by Pierre G with the modification that I'd use a hybrid common mode choke such as recommended by muRata HERE, and I'd also snub the bypass capacitor on the outlet side.

Cheers,

Terry

I hope it helps with this problem.


Running a Balanced System, With Twisted X-BoSoZ

[AndrewT]

Hi,
I see J Risch calls up 47nF (0.047u) for line to ground caps.

In the UK the maximum earth leakage on an RCD (RCBO) protected circuit is 25% of the trip rating.
Most systems are tripped at 30mA. This limits the total caps from line to ground to just under 100nF.
On that basis ALL the equipment on the same protected circuit should not exceed 100nF.

If you have suppression caps in other equipment then I suggest that the Filter caps to ground be reduced to either 22nF or even 10nF if your total is looking too big.
The Line to Neutral caps can remain at 47nF or even increased to 100nF.

[richie00boy]

Actually in the UK and Europe and likely the US too, any capacitors placed line (live or neutral) to earth must by Y-rated (open circuit in event of fail), and the total amount of capacitance allowed is 4.7nF.

[AndrewT]

Hi Richie,
I cannot access the document that my 25% of tripping current came from, but can I ask where your 4n7F came from.

If your much more onerous figure were to be applied, it would imply that very little equipment could share the same outlet from a distribution board circuit. That would make most domestic installations illegal on the 4n7F limit basis.

[richie00boy]

The 4.7nF limit is I suspect to ensure that multiple devices CAN be placed on a shared bus, yet still satisfy current and likely future RCD breaker standards.

I got my info from my year as a CE certification (included safety and EMC) engineer a while ago. The current standard at that time for appliance type equipment was BS-EN 60065 but I believe this has been superseeded.

[jleaman]

I wonder how hard it would be to build a ac power regulator. You know, like the one that monster makes and other comany's. They are complex i know that. Some start about 2500$ us each. They work well i was told. Would it be worth it to have tho is the next question..

Something like this ?

[martin clark]

Actually the 4n7 Y-cap is limited by safety considerations, because it links Live to Earth. Consider what happens if the equipments earth lead connection is defective. That's right, the casework could become live...

So - 4n7 limits the maximum leakage current to 0.3mA (at 240v AC); enough to give you a sting (it's about the perception threshold for AC), but not enough to cause serious hazard. And that's why, quite apart from breaker considerations, you musn't increase the value.

Have fun - safely!

[AndrewT]

Hi
What happened to my thanks?
Was it removed?

Well Richie thanks again for that info.
As I said I'll go and do a bit more research, now that I have a starter.