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 Minimising RFI from modern lighting
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 Return to top of page · Post #: 1 · Written at 2:17:14 PM on 28 November 2013.
Maven's Gravatar
 Location: Canberra, ACT
 Member since 23 August 2012
 Member #: 1208
 Postcount: 584

I'm losing my tolerance for the AM radio interference emitted by all modern lighting systems - fluoro, halogen, and LED.

Many of the fittings are not earthed, especially older reading lamps and the like. Compact fluoros and LED bulb replacements seem worse than fluoro tube fittings.

What's the best way to minimise this sort of RFI - earthing, shielding, some kind of capacitor across the line? No point in shielding the receiver, I suppose.

Maven


 
 Return to top of page · Post #: 2 · Written at 3:24:46 PM on 28 November 2013.
Brad's avatar
 Administrator
 Location: Naremburn, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 7290

I can't say I've had any issues with the LED lighting in my flat. That is to say my radios sound the same whether the lights are on or not. RFI is emitted by pretty much every mains appliance that requires an extra-low voltage to operate though as the common denominator is the switchmode power supply.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 3 · Written at 3:54:19 PM on 28 November 2013.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6678

As mentioned in another thread here somewhere, I have found that compact fluorescent bulbs are big RFI generators, and some are noticeably worse than others. Easy to prove -- I turn them off and the RFI noise in my sets stops.

I guess they are injecting the RFI onto the mains. I only have single phase power here so I can't try isolating by phase.


 
 Return to top of page · Post #: 4 · Written at 7:07:34 PM on 28 November 2013.
Simplex's Gravatar
 Location: Bathurst, NSW
 Member since 7 August 2008
 Member #: 336
 Postcount: 391

I only have one compact flurorescent bulb and it generates so much shocking RFI it blocks out the signal even on a battery powered transistor .

The colour range is pretty bad with these fluro bulbs to my eyes.

Have fitted either halogen or a few incandescent bulbs throughout the house and no problems.

The incandescents are in places where they are only switched on for short periods of time.

To save power.....just switch the light off when not needed.

Have not used any LED bulbs, they are pretty expensive.


 
 Return to top of page · Post #: 5 · Written at 8:17:11 PM on 28 November 2013.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6678

I only have one compact flurorescent bulb and it generates so much shocking RFI it blocks out the signal even on a battery powered transistor .

Actually, reading your post reminds me that I was going to try running one of my noisy CF bulbs via a 12/240 volt inverter to see if my old sets are picking up the RFI via the mains or through the air, or maybe both. From what you say, I can expect the problem to persist even if the mains are taken out of the question.


 
 Return to top of page · Post #: 6 · Written at 8:26:47 PM on 28 November 2013.
Brad's avatar
 Administrator
 Location: Naremburn, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 7290

LED globes are still relatively expensive but they have two payoffs. The first is longevity. They are said to last for 50,000 hours and being mass-produced and containing tiny electronics a few in every thousand probably won't last that long though the majority should come close. Of all the LED globes and tubes I have installed in the last few years both at work and at home, all are still operational.

Actually, the only LED lamps I have seen flame out are those of the cartridge type used in floodlighting. Nothing would be more disheartening to the owner of a $1,000.00+ LED lowbay light fitting than having it go blinketty blink blink like a dying fluoro tube and I've seen this happen to a few of them.

The technology is improving however and so is colour quality. Price is also coming down for LED globes with the traditional bayonet cap. I have 4 watt warm white LED globes in most rooms and these are perfectly adequate.

The chandelier in the lounge has three 6 watt LED lamps and the light fitting in the kitchen has one 10 watt LED lamp, all of these being in warm white. Before these I used compact fluoros but ended up changing because the light from fluoros is getting a bit harsh for my 42 year old peepers whereas the light from a LED globe is similar to that of a pearled incandescent globe of yesteryear. Before the CFLs, I used 100 watt incandescent lamps all round.

This brings me to the second payoff. LED globes and tubes use far less power than any other type of lamp. All my lamps added together add up to 48 watts - less than one traditional 100 watt globe. Together with my time-honoured habit of only burning lights that I am using, I am doing my best to keep my electric light bill as low as I can. Unless cashflow is an issue (and I know to many people it is) a LED globe or tube will pay for itself dozens of times over, well in advance of retirement.

I am not sure how to go about preventing the RFI issue that some members are experiencing. I know an isolation transformer won't work because most radios already have one fitted. A good quality mains filter, like those used for protecting banks of computer servers, may work although this would be prohibitively expensive and if any RFI is making its way to the radio over the airwaves then the filter will not have any effect. Inverters will not do the job because they employ switchmode circuitry like most power supplies have and would most likely make matters worse.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 7 · Written at 9:41:43 PM on 28 November 2013.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6678

Inverters will not do the job because they employ switchmode circuitry like most power supplies have and would most likely make matters worse.

Oddly enough, I have a switchmode plug pack near the radios and it doesn't produce the whine that I detect from CF bulbs.

I haven't tried my inverter yet, to see how it fares.


 
 Return to top of page · Post #: 8 · Written at 6:03:52 AM on 29 November 2013.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 830

When those CFLs do die, you can take it apart and find a few interesting parts inside. Like electrolytic caps like 20μF at 400V (test them, they can lead hard lives), some rectifier diodes and a few inductors.


 
 Return to top of page · Post #: 9 · Written at 6:58:46 AM on 29 November 2013.
Simplex's Gravatar
 Location: Bathurst, NSW
 Member since 7 August 2008
 Member #: 336
 Postcount: 391

The curse of the modern age, switchmode power supplies.

My mobile phone can generate RFI whilst charging, and one particular AA/AAA charger radiates like fury throughout the house wiring.

My Ferris 94 radio which is run off a power point in the garage picks the rotten thing up.

I have given up operating a valve radio in the same room where there is a computer.

Unless tuned to a strong local radio station.


 
 Return to top of page · Post #: 10 · Written at 9:07:15 PM on 29 November 2013.
Maven's Gravatar
 Location: Canberra, ACT
 Member since 23 August 2012
 Member #: 1208
 Postcount: 584

After reading these comments, I did a few experiments.

I noticed that there are two compact fluorescents in our bedroom, but the clock-radio does not pick up any interference. It is unearthed, double-insulated, but must have some effective suppression for its own internal PSU.

The light fitting there is earthed.

One of my vintage valve models picked up significant RFI from the same fluoros when plugged into the same powerpoint. The same radio picked up heavy RFI in a different room where the compact fluoro is in an unearthed mount.

I also noticed that RFI increased significantly when the external speaker was attached. This model Philips 123 takes feedback to the AGC circuit from between the output transformer and the speaker itself. It might be susceptible to the extension speaker leads acting as antennae and feeding ambient RFI back into the AGC.

This radio was itself unearthed, still having its original rubber figure-8 two core flex. I decided to finally bite the bullet and fit a 3-core flex with earth wire soldered direct to chassis. This almost eliminated all RFI, though there is still a 50Hz hum about 30db below tuned signal, independent of fluoro lights. It also gives a generally stronger signal.

One thing that might be a side-effect or might be unrelated is that the tone control circuit seems now to have little if any effect and AGC seems less effective. Could I have got a couple of connections switched in those feedback circuits?

Maven



 
 Return to top of page · Post #: 11 · Written at 11:35:44 PM on 29 November 2013.
Art's Gravatar
 Art
 Location: Somewhere, USA
 Member since 22 October 2013
 Member #: 1437
 Postcount: 896

Cheap inverters are the worst, they produce a fake sine wave that is more like a square wave.
I have run a modern LCD TV from one while camping,
and the noise it made was horrid.


 
 Return to top of page · Post #: 12 · Written at 1:12:42 AM on 30 November 2013.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

The catch 22 lies in the noise being radiated, or brought in on the mains. I do find that there is a tendency for RF to get through transformers and the worst problems occur in valve radios where there is no B+ decoupling cap.

The 123 if it is as I think it is (circuit on the other misbehaving computer. I just recovered mouse & keyboard on this one, yet again) does not cut out the internal speaker. That would change the loading and consequently the feedback.

As I have posted before: I have lightning surges & RF riding on the 24KV aerials. To reduce the hash there is a filter on the bench with (mains approved type) 0.2mfd active to neutral and two 0.0047μF one neutral to earth the other active to earth.

To trip up the spikes MOV N to A another A to E the latter is deliberately maintained for tripping out the RCD with a bad surge.

So far so good, in probably 30 years+ since the first one was tried (no RCD then) The 24KV line has been almost cut by lightning, one 24KV transformer blown up, brothers house same feed line, thousands of dollars damage due to lightening and lost count of the 24KV fuses.

In two separate locations where I have the protection, no damage. Think about that if you make a filter.

Marc


 
 Return to top of page · Post #: 13 · Written at 7:09:58 AM on 30 November 2013.
Brad's avatar
 Administrator
 Location: Naremburn, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 7290

Sinewave inverters are so cheap now that they should bring to an end the manufacture of the so-called modified sinewave ones which under the trade practices acts should be called a staircase wave because that is exactly what they produce. Iron core transformers tolerate this wave but only just and they run much hotter than they really should.

On the off-topic subject of camping...

Come to think of it, for a few years now portable generators have changed. Instead of crude alternators being coupled to equally crude two-stroke engines with the vain hope that they will run at exactly the required RPM so 50Hz will be produced we now have available units that are much lighter to carry that come with four stroke engines (no more mixing of odd two-stroke ratios like 40:1) and dynamos that produce a low voltage DC supply that powers a sinewave inverter to provide a quite stable 240 volts . 50Hz. These use the same inverter technology as the sinewave inverters you simply hook up to a 12 volt battery. These generators are also quite cheap (for what you are getting) and come with the added bonus of better fit and finish so there are no oil or petrol leaks either.

Marc raises a good point too. Aerial street distributors (power wires on telegraph poles) would be collecting AM radio signals from all over the world under certain conditions. Under the same conditions the medium voltage system he refers to would be force-fed signals from the high voltage state grids. Filtering it all out would be quite a challenge, assuming it was possible.

Burying the wires underground would not solve the problem as radio waves and lightning can penetrate the ground quite deeply.


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

 
 Return to top of page · Post #: 14 · Written at 7:17:12 AM on 30 November 2013.
Simplex's Gravatar
 Location: Bathurst, NSW
 Member since 7 August 2008
 Member #: 336
 Postcount: 391

Some years back had a problem with noise coming through the turntable pickup on my hifi system.
The noise took the form of a "thump" every time the refridgerator cycled.

Purchased one of these; http://www.jaycar.com.au/productView.asp?ID=MS4001

from Jaycar and installed it into a electricians box with a power lead and socket. Took care with proper earthing as per the regulations.

Plugged the fridge into the power outlet via this filter which happily almost totally reduced the "thump" to nothing.

The trick is to elimate the noise at the source although in many cases this would be very difficult to do.

I don't know whether the newer LED lights generate inteference.


 
 Return to top of page · Post #: 15 · Written at 12:46:46 PM on 30 November 2013.
Art's Gravatar
 Art
 Location: Somewhere, USA
 Member since 22 October 2013
 Member #: 1437
 Postcount: 896

That Jaycar EMI filter looks like little more than the caps
that Marcc suggested putting on the supply.
If the thing is useful, you could find out what the inductors are,
and ditch the modern looking box and/or PCB.
Can't complain about the price though.



 
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