AC/Input Filter

[yanz]

nothing special, really. i'm just bored seeing psus without a proper input filter. so i made it in it's own separated board. yes they're expensive. it cost me not less than $8.

but for PSU, usually i spend $2 or 3 for a smaller double choke, 2 caps type x2 (matsushita or philips), three leg power connector (moded).

[WeStSiDePLaYa]

what does the resistor between ground and neutral do?

[PlainBill]

Originally Posted by WeStSiDePLaYa

what does the resistor between ground and neutral do?

There is no resistor between ground and neutral. The resistor is between live and neutral.

PlainBill

[yanz]

it will limit the current when something 'bad' happens, i guess. cmiiw.
i got the pcb and all components from the shop and just tried to make that schematic.

[arneson]

It may be keeping the MOV happy.

[PeteS in CA]

Without R1, depending on what part of the AC sine wave you turn off power, the X-caps can be charged to whatever the peak voltage of the AC line is. And those film caps will hold that charge for a lo-o-o-ong time. Murata and TDK make ceramic Y-caps, and those might be less expensive than the film types you used.

[yanz]

Thanks for your explanation!


more schematic i 've found:

[Maxxarcade]

This is a good idea. I've got a couple drawers full of those dual chokes and X2 and Y caps that I've salvaged from parted out monitors and power supplies, and now I know what to do with them.

But I have a couple questions- Does anyone know how much it actually reduces noise on the line, and does it make the PSU any more efficient by reducing inductive kickback to the mains? I'd be willing to do some tests with the scope and other equipment if I get the time.

I'll find out soon if adding an input filter helps my AM radios, since I'm replacing the two cheap psu's in my servers with nicer filtered Sparkle units this weekend. The cheap psu's have no filters at all. They are connected to UPS's though, so maybe I won't gain much in that case.

[Per Hansson]

Originally Posted by Maxxarcade

They are connected to UPS's though, so maybe I won't gain much in that case.

Depends if the UPS runs the inverter all the time or only when the power goes out...

If it only runs the inverter when the power fails it does not modify the voltage when it is "within spec" that is within 208-253v on a APC Smart-UPS 1500 set at "high" sensitivity for example...

[larrymoencurly]

Originally Posted by Maxxarcade

Does anyone know how much it actually reduces noise on the line,

Compared to nothing at all, it can make a huge difference. I listen to a weak AM radio station, and my MaxPower PSU with no AC line filter would blank out that station even when located twenty feet from the radio and plugged into a different AC line (different circuit breaker). OTOH my Delta PSU runs only three feet from that radio, is plugged into the same wall outlet, and causes no audible interference. I added a line filter to the MaxPower, and it became just as quiet, even though the filter had one less choke than the Delta's.

[Maxxarcade]

Well, I don't know if it is coincidence or not, but I just tried my AM radio after changing out the power supplies in my servers, and now I can get many stations instead of just 1 or 2.

Most stations were just 120Hz hum before. Makes me wonder... I'm just glad I didn't mess with the RF trimmers in the radio.

BTW the radio is a Philco 46-420 that used to be my Grandma's. I got it running by replacing all the old paper caps with high grade Sprague Orange Drop caps

[999999999]

If you are making your own boards, others who make boards might benefit from attaching the etching (and sometimes label) patterns.

I had thought about something like this but putting it in a large metal, multi-outlet box. I just hadn't decided yet if I wanted every single outlet to have separate filters, but going that way is a lot easier to find chokes, as most I have aren't large enough to support several outlets worth of gear.

[arneson]

Would that look like this, Maxx?

[Maxxarcade]

That's the one It still has the original back panel as well. I replaced all the caps, including the multi-section filter cap. Also had to replace the dial string, power cord, pilot light, a couple resistors, and a tube socket. It was my first tube chassis repair, and turned out better than I expected.

I'm surprised how good it sounds for it's size and age. It appears to have an Alnico magnet on the speaker (earlier version was field coil, this one is a code 125). The tone is surprisingly rich.

Next up is a Philco 41-300 console that I picked out of the trash, and an RCA R-8 Tombstone radio from the early 1930's. Problem with that one is being able to find a new power transformer, it was a bit unique, and the original one is melted into a glob

[arneson]

Ebay is your friend.

[starfury1]

well following on from Yanz's original post

Found this site on coils inductors transformers etc ,really a sales type site but has lots of info pdf's by the looks of it
So if you wondering what that EMI inductor coil might be capable of this site may help
EMI RFI

Thanks Yanz, it is an interesting topic and one that doesn't come up very often
--------------------------
Ooh Valve Radio they are really nice to listen to and look at when restored well.
They build things to last in those days, well to the best extent of the technology of the day

shame we don't get this quality today

I have a one.
Last time it was service was in 1965, (built in the 40's I believe)
Really must look at trying to restore it.
time time time, where does it all go

[Logistics]

The bypass capacitors, depending on value, filter out different frequency ranges. If I recall correctly, in many circuit, before IC's, the suggested combination is a 0.1uF, 0.01uF and 0.001uF or 100,000pF, 10,000pF and 1,000pF. Maybe it's different when you're dealing with mains, but I can't imagine why. EMI/RFI happens in either case.

Question: In the first schematic in the thread, there are pairs of caps before and after the inductors, C1a+C1b and C2a+C2b, respectively. When wired in parrallel like this, won't that cause the two capacitors to act as a single capacitor of half the capacitance?

[PeteS in CA]

Nope. Caps in parallel add, so two .1s in parallel equal .2uF; OTOH, two .22s in series equal .11uF. Basically, it's the reverse of the series and parallel rules for resistors.

[rxtxau4]

Fit a heatshrink sleeve to the MOV.

You will often find commercial circuits have a heatshrink sleeve fitted over the MOV. It is there for a very good purpose.

More than once I had to work on gear after lightning storms. If there wasn't a heatshrink sleeve over the MOV I soon fitted one.

More than once I powered a board up & the MOV exploded. One even destroyed the PCB under it but normally when they went bang bits went everywhere. Some times near by components were casualties. The first time one got me it left me with a bleeding forehead & nose. Too close to my eyes for my comfort.

The MOVs may explode immediately the board is powered up or they may wait for a while.

The lesson is simple. Fit heatshrink sleeves & replace a MOV if there has been a close lighting hit.

[Longbow]

Great job on the construction. A couple of comments on the circuit: disregarding the x-y caps for the moment, this is a low pass pi-network noise filter. What makes it unique is that the network is symmetrical (has L in each leg) and that there is inductive cross coupling between the windings. The inductive coupling improves the stop band (high frequency) cancellation and is effective when both source and load impedances are low. But the values of inductance and capacitance are important for the filter to work. Most inductors are not marked so they would have to be read with an inductance bridge. Secondly, the wire size used on the inductors needs to be matched to the current requirements of the power supply. Seems like a simple enough circuit until you look closer.