EMI filter before transformer, good or bad ?

[Dannyx]

Good day folks. I'm using a UPS transformer to power a project. A while ago I gutted some ATX power supplies and one of them had the EMI filter as an individual board, separate from the rest of the board. I took a picture, though the angle's a bit sh!t, so I can take better ones if need be, but for now let's just discuss the general idea. Would it be a good idea to put this thing before my UPS transformer ? Would the effect be:
a) beneficial
b) detrimental
c) useless

In hindsight, I already did it It obviously works, but not having any fancy measuring equipment, I don't know what I should look out for. A SMPS is very different from a transformer like this.

[budm]

Re: EMI filter before transformer, good or bad ?

You can read this and see if you will want to use it or not:
http://www.futureelectronics.com/en/...mi-filter.aspx

[Dannyx]

Re: EMI filter before transformer, good or bad ?

Some sources say it's not a requirement but doesn't hurt to have it either, so it would be C

[japlytic]

Re: EMI filter before transformer, good or bad ?

I've seen X and Y class capacitors lose capacitance throughout their electrical life (and therefore, EMI filtering is degraded), so they should be checked (with one end disconnected) after discharging them, or they should be replaced with new ones.

[electroyeti]

Re: EMI filter before transformer, good or bad ?

Hi Dannyx,

Just my 10p worth. If the components in the filter are still servicable then it will do no harm.

I am a radio amateur and can verify that EMC filters do help to reduce or eliminate Radio Frequency Interference.

Just be sure that the current rating of the EMC filter is sufficient for the current you will be passing through it though from the picture it should be good for a few Amps.

Cheers,

electroyeti.

[eccerr0r]

Re: EMI filter before transformer, good or bad ?

It could be all three...
If you have no sensitive radio equipment anywhere nearby, then (C)
If you do have sensitive radio equipment nearby, then (A)
If you're running any type of data over power line on that leg or need to draw near full current of the source outlet and the inductor can't pass that current, then (B).

[Dannyx]

Re: EMI filter before transformer, good or bad ?

It could be all three...
If you have no sensitive radio equipment anywhere nearby, then (C)
If you do have sensitive radio equipment nearby, then (A)
If you're running any type of data over power line on that leg or need to draw near full current of the source outlet and the inductor can't pass that current, then (B).

It's powering an ebay PSU module we talked about in a previous post (you may remember about it, since I believe you joined in as well): stick a rectifier and 2 caps on the output and feed 40v into the input of that adjustable regulator.

[eccerr0r]

Re: EMI filter before transformer, good or bad ?

Yep, but I don't know if you're running unrelated sensitive radio equipment, X10, etc. nearby

Likely the filter will not do anything good or be bad for the power supply itself.

[Dannyx]

Re: EMI filter before transformer, good or bad ?

I believe it requires an EMI filter if I were to try and build it "to spec"

[eccerr0r]

Re: EMI filter before transformer, good or bad ?

Depends on your country. In the USA, the FCC puts out the laws so radios aren't completely useless when people start using switching power supplies.