Wall wart question

[Chris Hogg]

I'm tired of putting up with the interference on AM/FM radios that happen to sit too close to a switched-mode wall wart needed for another item. Is there any way I can suppress the interference, like putting ferrite rings on the DC output from the wart, or wrapping it in aluminium foil, or whatever? If no solution in that direction, how can I tell if a wall wart I might see on e-bay is switched-mode or the older transformer type that I assume doesn't create interference?

[Peter Parry]

Looping the output cable several times around a ferrite core or through a ferrite ring will give some reduction but see later.

probably won't as you couldn't earth it and could be potentially lethal if the foil or whatever came loose and in contact with the mains pins.

The switched mode will be a lot lighter so if postage is less it may give a clue. Most of the Ebay Chinese switched mode offerings are pretty dire and noise suppression is something which has to be designed in from the beginning, it can't really be added as an afterthought.

If you buy from the likes of CPC.co.uk it will cost a bit more but there is at least some chance the thing will actually meet the various standards marked on it. On the direct imports CE simply means "Chinese Export" and they make pretty neat broadband jammers. They are also amazingly optimistic with current ratings.

[Martin Brown]

Decent well designed wall warts should be reasonably well behaved. Be surprised if they jammed FM except at very close range. AM tends to be super sensitive to badly designed switched mode PSUs.

You can get clamp on ferrite rings that will stop some of the interference but buying a better wallwart might be better.

How well they work is another matter. It might take the edge off something that is borderline but it won't work miracles.

Moving sensitive kit away from the source of interference is probably a better bet.

eBay Chinese imports you are lucky if they are electrically safe.

Any modern PSU will likely be switched mode these days (although the price of iron going through the floor might change that).

Is there a market for old ferrous transformer based wallwarts?

Regards, Martin Brown

[tabbypurr]

Get a 2nd hand iron lump type wallwart. Be aware most are not voltage regulated, so offload voltage rises. Some equipment is not ok with that. More info needed.

There are other options.

NT

[Capitol]

No, they are just using American Amps, these are about 3 times a UK Amp and achieved at unbelievably low temperatures, attached to an infinite heat sink! Most semiconductors are now always rated in American Amps because they look better on paper before they self destruct. I used to rate power semiconductors for reliability in the dim and distant past. International committee meetings were a hoot!

[Capitol]

I have seen production Asian switched mode psus, where the CE marked units had the suppression components removed after approval was obtained! All the mounting holes were in the PCB with shorting links inserted where necessary.

[Theo]

I like this 'power supply':

Though note that weight isn't a reliable indicator either:

Theo

[therustyone]

e?

The wall wart I got boxed with a new Sony DAB/FM portable gave out bad interference on FM, probably they never tested it in a Japanese fringe area. Replaced it with an old heavy iron transformer PSU and no more problems.

[Peter Parry]

Unlikely - see below.

Linear external power supplies were effectively killed off by European Directive ErP (Energy related Products) 2009/125/EC (and similar American regulations). The related "COMMISSION REGULATION (EC) No 278/2009 of 6 April 2009 implementing Directive

2005/32/EC of the European Parliament and of the Council with regard to ecodesign requirements for no-load condition electric power consumption and average active efficiency of external power supplies"

This requires external power supplies to have efficiencies and no-load power ratings which linear supplies cannot meet.

[Brian Gaff]

I've tried them all plugging it into a suppressed outlet, ferrites earthed biscuit tins etc, but the main problem is that they are badly designed and saturate the core on the tiny transformer used to step down the voltage via a free running oscillator connected directly to the mains via a crude rectification circuit. I've trawled around many peoples junk and found some of the old heavy normal type supplies and added conversion plugs on the end to fit the equipment, No not as efficient much bigger but oh, the bliss at least until the neighbour starts recharging their laptop or the power line internet adaptors two doors down are switched on, then its hash gurgle and buzz from long wave all the way up to over 50 megs in various bands and wandering burbling carriers and screeching noises from the ticking power line devices.

To my mind we should have an electronic equivelent of the noise abatement society. Short of moving into the middle of a field somewhere I doubt things will go back now. Too many Chinese imported crap generators. Brian

[spuorgelgoog]

Are they related to Argos Watts?

Owain

[Cursitor Doom]

+1. They're making the radio spectrum into the equivalent of an unlicenced rubbish tip.