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 Any wonder some SMPS distribute tons of RFI?
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 Return to top of page · Post #: 1 · Written at 3:57:44 PM on 26 August 2020.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6013

Here is a switch mode power supply sold in the UK by Maplin -- their equivalent of Dick Smith Electronics, and like DSE now merely an online shop.

Presumably sourced from China, this effort serves to show the cynical disregard exhibited by such manufacturers towards regulations regarding Electromagnetic Compatibility (EMC).

Maplin Switch Mode Power Supply


 
 Return to top of page · Post #: 2 · Written at 4:46:28 PM on 26 August 2020.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6352

I didn't think Dick Smith was still around. After some brief research, it's a branch of the Kogan empire now. So be careful when ordering off them, if they are like their new big brother, your inbox will be flooded with spam every day.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 3 · Written at 4:49:50 PM on 26 August 2020.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6013

it's a branch of the Kogan empire now

Yep, and Kogan's prices are way over the top.


 
 Return to top of page · Post #: 4 · Written at 6:00:06 PM on 26 August 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1910

The reason the mains filter parts are left out is simple - the CE regulations regarding conducted emissions have changed.

This has nothing to do with switched mode and nothing to do with RFI. A diode bridge feeding a capacitor generates harmonics into the low MHz range that get fed back into the mains. Those components were there to attenuate the harmonics. Now that Europe had abandoned the MW band the rules have changed and there is no longer any reason to stop this very common occurrence from happening.

Cynical?


 
 Return to top of page · Post #: 5 · Written at 6:41:34 PM on 26 August 2020.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6013

This has nothing to do with switched mode and nothing to do with RFI.

Huh? The harmonics from this PSU were wiping out 6 metre comms for miles. That's RFI in my book.

there is no longer any reason to stop this very common occurrence from happening.

See above.

Cynical?

You can drop the sarcasm.


 
 Return to top of page · Post #: 6 · Written at 7:18:31 PM on 26 August 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1910

Actually from my experience it's doubtful if the absence of the line filter would affect EMI in the VHF region, more likely it's a badly-designed or absent snubber on the flyback switch. Or possibly just an omitted ferrite bead.

Snubbers are probably the main cause of EMI in the VHF region in flyback power converters. To work properly they need to be critically tuned to match the transformer. What often happens is the transformer design changes in production but the snubber doesn't.

I wasn't being sarcastic, I was suggesting that leaving the line filter out because you could get away with it was a cynical exercise.


 
 Return to top of page · Post #: 7 · Written at 9:45:42 AM on 27 August 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 882

Looks like a typical Asian "take a photograph of it " clone copy of something that was actually designed right in the first place by a UL spec buisness.
We had Asian suppliers who could take a photo and send you a sample in 4 weeks.
Anything you like. Cheaper.
They would just leave out parts not required to make it work.

I had samples of product for testing that included an original device's poor design or mistakes exactly copied!

How many you want, what colour?
No ploblem, we send more!

Fred.


 
 Return to top of page · Post #: 8 · Written at 10:06:41 AM on 27 August 2020.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1380

I'm surprised they didn't link out the fuse, and remove that greenish thing next to it.


 
 Return to top of page · Post #: 9 · Written at 10:19:02 AM on 27 August 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1910

Yes my thoughts also.

Re the filter removal, there is a legitimate case for its removal if slow diodes are used in the bridge, allowing you to get the conducted emissions down below the curve.

There is also a "cheat test", to do the conducted emissions test with no load on the P/S.


 
 Return to top of page · Post #: 10 · Written at 11:55:50 AM on 27 August 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 882

Hey, Ian, we had suppliers who thought that any testing required was met by putting the appropriate logo on the product!!
C tick? "No ploblem!"
UL, "No ploblem!"
Emission standards ?, "No ploblem, give us the numbers and we put on for you!"

Certification papers? "We send", they never did or sent something meant for something else or downloaded from some other suppliers web site!

I used to just sob quietly and go away.
Purchasing could never see any problem, if the paper work is filled in correctly with the correct numbers what is the problem?
Bloody engineers, always getting in the way of a good deal.

Fred.


 
 Return to top of page · Post #: 11 · Written at 6:57:12 AM on 28 August 2020.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 766

I've used the circuits of the missing parts as powerline/mains RFI filters on table/mantel radios.
RFI filter mod for radios

I usually take dead power supplies and cut the portion of its circuit board that houses these parts, to use as a module inside the radios.


 
 Return to top of page · Post #: 12 · Written at 10:44:34 AM on 28 August 2020.
Trobbins's avatar
 Location: Melbourne, VIC
 Member since 11 July 2012
 Member #: 1179
 Postcount: 42

GTC,
Was the smps sold as a pcb assembly for installation in to OEM type equipment, or as a standalone item of equipment in a shielded enclosure again for installation in to OEM equipment, or as a standalone item of equipment that could be used in a domestic environment ?

How were you using it such that it degraded VHF comms?


 
 Return to top of page · Post #: 13 · Written at 8:11:02 PM on 28 August 2020.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6013

.Trobbins: that PSU, sourced from Maplin, was in a home-built PC put together by a young guy in London. He was blissfully unaware that his PC was wiping out comms on 6 metres until he was door knocked by local hams who'd had enough and used direction finding techniques to locate him. Fortunately, when the owner was shown what effect his PC was having on radio communications, and it was pointed out that the source was his PSU (photographed), he agreed to replace it with a higher quality PSU and the problem went away.

The Maplin PSU was managing to generate harmonics that affected 6 metres. It was possibly affecting other bands as well, but it's the 6 metre users who were galvanised into action.


 
 Return to top of page · Post #: 14 · Written at 9:14:24 AM on 29 August 2020.
Trobbins's avatar
 Location: Melbourne, VIC
 Member since 11 July 2012
 Member #: 1179
 Postcount: 42

Ahh, so by home built, does that mean it was totally up to the buyer to correctly deploy the smps in such a way that EMC from the final 'product' was compliant to amy and all standards?


 
 Return to top of page · Post #: 15 · Written at 9:32:06 AM on 29 August 2020.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6013

My understanding is that it's the power supply manufacturer's responsibility to comply with EMC requirements. It would have been interesting to see what, if any, certifications were claimed by the manufacturer in that case. Clearly the filter components had been deliberately omitted.

As for end users, they may or may not accede to requests to cease and desist using noisy gear. It usually depends on how they are approached. Diplomacy usually wins the day.


 
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