choke \ mains filter

[stewart]

ok guys, im trying to put together a mains filter. well 2 actualy, one for pc, the other for entertainment system.
got myself some x and y caps, and a few mov's. question is, related to winding a choke.

is there an optimum number of turns?

is it better to have both coils on one ferrite ring, or seperate rings?
(if im remember here, one is wound clockwise, the other counterclockwise)

ta

[PeteS in CA]

Re: choke \ mains filter

Without tens of thousands of $$ worth of equipment, "optimum" just doesn't fit your circumstance. Your more in a anything will do something situation. That isn't a put down since the same would apply to me.

There are two kinds of inductors commonly used in a filter. The differential mode inductor has a single winding and typically uses a powdered iron toroid (donut-shaped) core. Micrometals type 26 or 52 material would be good choices. Pick a decent size and put lots of turns on it. AWG #20 should suffice for 4A or less; AWG #18 for 8A or less.

The common mode inductor has two windings and usually uses a 5000 or 10000 permeability ferrite core (Magnetics Inc., Fair-Rite, Ferroxcube, MMG and TDK are good brands). You need to use insulated wire (not just the varnish on magnet wire) or use polyester or similar tape to insulate the core to avoid shorts to and through the core. The two windings should be done on opposite sides of the core; safety agency regs, , require 8mm spacing between the wires if they are not insulated (e.g. magnet wire, where the varnish is not considered to be insulation) or three layers of insulating materials between the wires. The starts of each winding should enter the core from the same side when you do the winding, and the starts should both be either the input or the output side in your filter circuit. Each winding should be the same number of turns.

If you aren't scared out of your mind by the above and are still awake, , I'd suggest finding a couple of dead P/Ss and using their inductors. Realistically, finding and obtaining the toroid cores may be rather difficult.

[arneson]

Re: choke \ mains filter

I've read a lot of good online DIY power filter projects.
The toroids are coffee can size,two three or four of them.
Sorry I no longer have the links.
I've been using the Pure AV units off Ebay, get them blown for almost nothing.

[PeteS in CA]

Re: choke \ mains filter

Digi-Key has power entry modules and filters-in-a-can here. Corcom is a good brand; haven't heard of the other company. Digi-Key also sells ferrite toroids made by D. M. Steward. I think the ones at the top of the page should be generally suitable, thought the catalog doesn't give the permeability.