Need Help with EMI/RFI Line Filter

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Hi:

I 'm wondering if someone could give me some pointers on how to wire a high current EMI/RFI Line Filter.

A while back I found a large (8"X15"X2") West-Cap AC EMI/RFI Line Filter. It is specified as 250 VAC 2X30AMP.

The filter is a large square tin box with 2 screw terminals on the input side and 2 screw terminals on the output side. There is no terminal for ground; I assume that it is just the metal case.

Some questions:

1) This appears to me as a "single phase" line filter. Live + Neutral for the input terminals and the case is ground.

Why is it specified as 2X30 AMP?

Many filters that I have seen including the ones built into the IEC modules are just specified as 10 AMPs.

2) How do I wire this filter?

Smaller EMI/RFI filters are wired "Live" to one terminal and "Hot" to the other terminal with "Ground" to the case.

When I wire this filter in this configuration, I get a sizable current draw even when there is no load on the filter.

Any ideas?

Many Thanks!

Derek
 
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Joined 2005
2 input terminals and 2 output terminals sure sounds like line and neutral in and line and neutral out.

How much current is "sizeable"? Can you open it up and snap a photo or draw up a quick schematic?

The common mode choke in most filters is two windings (line side and neutral side) on the same core. 2x30A most likely means that both sides of the filter are rated for 30A.
 
Hi Brian:

Thanks for your reply.

When testing "unknown" devices I wire a 100watt light bulb in series with the load to provide current limiting.

With the neutral connected to one terminal and live to the other the bulb glows about 35-50% brightness. There is no load on the filter.

Derek
 

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I'm a little confused because you said you wired the light bulb in series with the load but you also said there was no load on the filter.

Did you mean you put the light bulb in series with the line input to the module and left the output terminals open and the light bulb was lighting up?
 
Hi Brian:

When I wrote wiring a load in series with the light bulb, I was referring to the Line Filter as the "load."

To clarify, the "input" of the line filter is wired in series with the 100 Watt light bulb.

There is no load attached to the output of the line filter.

When I power the line filter up with the light bulb in series, the 100 Watt light bulb glows to about 30-50% brightness which is a good current draw with nothing attached to the output of the line filter.

Thanks,

Derek
 
Ex-Moderator
Joined 2005
The only way to find out for sure is to open up that sucker and see what's inside :)

Most filters have a large value resistor between the line and neutral but that sure shouldn't cause a light bulb to illuminate as much as you saw. Maybe some cap inside has shorted out? How old is that monster?
 
Hi Brian:

From the schematics online of similar filters, I have noted a 470K bleeder resistor between the live and neutral to discharge the capacitors.

I don't know how old it is, but probably a few years. I picked it up in "new" condition at a surplus store. It was in a card board box without notation.

When I put an ohm meter across the input I can see the caps charging up.

I'm still a little bit thrown off by the 2X30 amp designation. I understand your explanation, but not sure why nobody else such as Corcom etc... expresses it this way.

Can this thing be used "single ended?" Perhaps just leave one set of input/output terminals disconnected. And then feed the live in series with the with filter on the other set of terminals?

Derek
 
Hi Brian:

My friend thinks this it is designed for 240 V or 208 V feeds like the ones coming into our houses and which power the stoves and dryers. I.e. Two out of phase hots at 240/208V, but 120/104V from eithr hots to neutral.

There is no neutral connection on the filter. The terminals are both for the hots and the case is grounded.

If the two inputs to the filters are driven out of phase, the current draw may drop.

The question then is, can it be used in single ended mode for 120 V operation?

What do you think?

If I open it up, I'll learn something but then I won't be able to use it anymore :(

Derek
 
Ex-Moderator
Joined 2005
I think your friend is right.

As for using it single ended - I wouldn't just because it was not intended to be used like that. Like I said before, I wouldn't feel comfortable using it how you want to without knowing what's inside first. There's no easy way to open it up without destroying the enclosure?

You could always use it between a 240V outlet and a 240V appliance and see if it cuts down on junk spit out on to the other AC lines in your house.
 
maybe there is a rather large value filter capacitor inside it and the reactive loading of the capacitor at 60Hz causes the light bulb to glow? large capacitances are sometimes used for power factor correction with inductive loads......

much like those small off-line supplies that use only a capacitor to limit current to a low voltage load....

usually, these filters are sealed by soldering the case. opening it is by using a blow torch or similar to melt the solder holding the case together.
 
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