radio interference from light dimmer

I have one of those "touch lamps". As you touch the metal shaft, it cycles though: off, dim, medium, fully on using a Triac.

The unit kicks out terrible radio interference, as expected this is worst at dim and medium, though off and fully on are not completely clear.

It's worst around 6MHz (49m short wave), continuing upto 30MHz. The top aof medium wave (1.6MHz) is also pretty bad. Lower medium wave and long wave are somewhat better. It sounds like a buzzing noise.

I don't really know if the interference is conducted or radiated.

The unit is marked CE, so I would have expected care in the design to smooth out sharp switching edges and corners to avoid this, but not so.

I have some mains voltage rated capacitors (only 1000pF which is a bit low), and have tried connecteing across the 240VAC supply at live to neutral, live to ground, neutral to ground. None made any difference.

I've not yet tried capacitors across the light bulb, but will do.

Anybody on here had a similar experience and fixed / reduced the problem.



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I'm also going to try swapping live and neutral on the power cord. Googling seems to show an inductor in the power lead + a capacitor as part of a suppression circuit, but it's tough for me to get inside the "brick".

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You can try those clamp-on ferrite chokes, and not just as common-mode filters; route the two wires that go to the lamp from the black box through a single bead but in opposite directions. It might take an R-C snubber (something like 100 ohms in series with .0047 uF) on the dirty side of the choke, to keep the black box triac happy.

Don't connect any capacitors to the ground wire, only hot/neutral/ switched. There are good power-line filter assemblies, with all the regulatory approvals, available for the AC input side. Buy one (or recycle from roadkill electronic items), it isn't worth building your own.

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Thanks, I do actually have an AC power line filter "assembly" from an old washing machine which I'll try. Shame on CE. Or shame on companies that simply mark their products CE. Surely this can't be compliant??

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** Likely it is both.

** It lacks a suitable inductor in series with the load - about 1 mH does a fair job.

A class X cap across the incoming supply will help a lot too.

..... Phil

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Phil Allison

If it is an old lighting fixture there is a not unreasonable chance that it was compliant at the time it was built. Nor is it unreasonable that it has gone out of compliance with the older standards as it has aged. If it is a new device you have a legitimate complaint worth alerting enforcement types.

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