Installing transient filtering

[phoenixlament]

According to HardwareSecret's Anatomy of Switching Supplies Tutorial, some cheap power supplies do not include transient filtering components such as the ferrite coil, X capacitors and y capacitors.

I just fixed power supply 1 (replaced thermistor) and noticed that it does not have complete transient filtering(only has y capacitor). However it has all the correct empty spots on the circuit board where the transient filtering components are supposed to go. (Refer to hardwaresecrets link, that page goes into further detail)

Power supply 2 is lying around and is beyond repair (almost all caps are leaking with burnt mosfets and diodes). However it does include the transient filtering components: ferrite coils, X capacitors, Y capacitors


I've removed the ferrite coils and X capacitors from supply 2 and I'm about to attach it into the same spots on supply 1. Here is my question:

Are the ferrite coils and X capacitors polarized? In other words, does one end need to take in positive current and the other end, negative?

I've uploaded some images, but not sure how to use the IMG tags properly. Could someone please show me how? Images would definitely clarify things.

Thanks a lot!

[etnietering]

Re: Installing transient filtering

None of that stuff is polarized, so you should be good to just throw it in there (if it fits). The two X caps should be fine, and the big square coil, but the toroidal (round) coil only has 2 leads, so it will only be good for one side of the second coil spot. I don't know if it'd be worth it to try to rig that one in there or not...
looks like you really nuked that power supply too! ouch!

edit: oh yeah! make sure to install the coil in the correct orientation. if you install it wrong it will short the mains and blow your circuit breaker (or catch on fire)

[etnietering]

Re: Installing transient filtering

ok it wouldn't let me edit it again...anyways

you should also take the blue Y caps out of the dead PSU and replace the ones in the working PSU. The blue is usually an indication that they're Y class safety certified, where as the little brown ceramic ones probably aren't.

for the images, I right click the name of the attachment after I upload it and select 'copy link as' then I click the little insert image button above the text box and paste the link into it. it's quite easy, once you know what to do

[370forlife]

Re: Installing transient filtering

That second spot with the two jumper wires is also a spot for a coil. Just remove the jumpers and put another in.

ohh, and to use the img function, just upload the image, and in the manage attachments before you submit the post you can view them. View the desired one, copy the URL, close it, click the yellow img button and paste the link into it.

[phoenixlament]

Re: Installing transient filtering

Successfully installed transient filtering! Put in 2 ferrite coils in place of LF1 and LF2 and 2 ceramic capacitors for CX1 and CX2. Made sure that the ferrite coils were placed the right way. PSU works, although I have no oscilloscope to see how much better it is with the filtering.

By the way, this "upgraded" PSU is an OKIA 450-ATX.

Check this pimped out PS-Unit yo.

Before:

After:

Overall:


Pimped!

[etnietering]

Re: Installing transient filtering

nice job! don't try to get 450W out of it though, or it'll look like the one you took the parts from...

[370forlife]

Re: Installing transient filtering

Thats the same yuelin platform as the one I rebuilt. Secondary side is a bit different.

[phoenixlament]

Re: Installing transient filtering

Thats the same yuelin platform as the one I rebuilt. Secondary side is a bit different.

yeah i checked out your yuelin, it does appear very similar.

nice job! don't try to get 450W out of it though, or it'll look like the one you took the parts from...

of course not, this thing will be powering a low end pentium 4 with a mediocre AGP video card, one hard drive, and one CD drive. No plans for high end gaming, will use this for networking and linux experiments.

thanks for the tips y'all. this forum is proving very helpful and you guys really know how to help people get stuff fixed. glad to be part of the community.

[japlytic]

Re: Installing transient filtering

Sometimes, such filtering may not be included if most of it is included in a shielded IEC EMI filter.
Otherwise, that is cutting corners.

[momaka]

Re: Installing transient filtering

Great work phoenixlament!

PSU works, although I have no oscilloscope to see how much better it is with the filtering.

Unfortunately, the input filter doesn't do much for the filtering on the output side of the power supply (it only reduces EMI from going back in the line which means less interference with other electronic devices as well as it supresses most voltage spikes that damage the primary capacitors).

Since you're going to use this in a P4 system (most are 12v-based), you will also need to do a bit of work on the secondary side. Notice how it has empty spots for more capacitors and jumpers instead of PI coils. Both of those are responsible for clean DC output (which is vital for a stable system). Hard drives are usually the most sensitive to fluctuations, so a 12v rail with lots of ripple can kill over time.
I suggest using at least one 16v 3300uF cap or 2x 1500uF caps for the 12v rail. 5v rail and 3.3v rails should suffice with 2x 1500uF caps (though having 2x 2200uF is usually the standard).
As for the PI coils, see if you can get them from other junk PSUs.

[370forlife]

Re: Installing transient filtering

Also those 4 diodes next to the main caps should be taken out and replaced with a bridge rectifier.

Those diodes look like they are maybe good for 2A or so...