LED driver interference on FM!

ard126k

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This weekend I put some trendy LED striplights in my kitchen. But when I switch them on I have interference on my old Tandberg FM portable set. It's a sizzling/whooshy noise, not like mains hum. The LEDs are powered by something calling itself an "Electronic LED converter" which claims to be a switch mode power supply. If I unplug the LEDs from the PSU the interference stops. The radio is using its own telescopic aerial. Does anyone have any ideas about fixing this please?
 
1. Relocate the radio as far as possible from the led lamps and wiring.
2. Adjust the aerial positioning (and fully extend it if not already) to maximise radio reception and minimise interference pickup.
3. Don't use the leds when listening to radio.

You could try changing the leds or psu or the combo to see if they are faulty - but I suspect it's the proximity of an interference source (plus the wiring acting as a 'radiator' of interference) and the radio receiver's aerial.
 
I wonder if that switch mode power supply is CE approved; if it is that noisy, probably not (or could be faulty).
 
Thanks for all the ideas. It's a bit hard to move the radio away from the LEDs because they light up the worktop where the radio sits!

The PSU has a CE mark,and several others I don't understand, and in its accompanying leaflet it claims to conform to 2004/108/EC for electromagnetic compatibility. So it should be quiet????

Alex.
 
To see if the interference is being radiated or conducted, try temporarlily screening the PSU with silver (aluminium) foil).
 
Would running the radio on battery power help to determine whether the interferecne is conducted or radiated?
 
I tried the foil method,no difference. BTW the PSU isn't earthed,that can't be helping?

I think it must be radiation because if I unplug the LEDs from the PSU the noise stops,and if I wave the radio aerial about the noise comes and goes. I think I'll just find the aerial position of least interference and live with it. Disappointing though,the LEDs weren't cheap!
 
Sounds like radiation (possibly with some conduction also).
What happens if you run the radio off batteries ?
What is the DC supply from the PSU ?
Have you considered trying putting a capacitor across the DC side (to short out any conducted RF at 80-108 MHz).
You could also try winding cable through ferrite rings, putting ferrrite beads on the cable and consider too the snap-on type for inaccessible places (but they cost more).
Maplins and similar places should sell the ferrites.
 
I have had similar interference problems from MR16 12V halogen replacement LEDs in a bathroom. These problems are definitely caused by the 'switch mode' power supplies that are built into the lamps to control the current through the LEDs. LEDs themselves don't cause interference.

I fixed the problem using 25-35mm ferrite rings bought from Maplin (stock code N88AB or QT26 - the N88 is cheaper).

Disconnect the two leads from the ceramic lamp socket where it is connected to the wiring from the transformer. Then feed the two leads through the centre of the ferrite ring and wrap each lead round the ring, as many turns as the length of the leads allows (3 turns each in my case); the ring should then be sitting just above the lamp socket with two short leads projecting above which should then be reconnected to the 12V feed from the transformer. Refit lamp as normal. Fit these rings to each lamp that is installed.

This largely fixed a problem with interference on FM radio (I am in a relatively weak signal area); I now only see a problem if a radio is within a few feet of the lamps. Extending the lamp leads to get more turns around each ferrite ring would probably reduce the interference further.

NB electronic 12V lamp transformers can also cause interference; it is always best to use the old style (heavy) wound transformers for supplying MR16 LEDs (one transformer will normally supply several LEDs).

Incidentally I did try some of the fixes that Chris suggests: a 220nF disc ceramic capacitor across the dc supply inside a lamp made no difference - rather surprising. Ferrite beads (Maplin N98AB) did make some difference but not enough to fix the problem - might work in milder cases.
Hugh
 
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