X10 and Compact Fluorescent Bulbs

Jeff Volp  (5-12-07)

Some countries are planning to phase out the use of incandescent light bulbs over the next several years.  Whether this really happens will remain to be seen, but we can expect that compact fluorescent lights (CFLs) will be used in more residences as time goes on.  Because of their nature, CFLs can cause a problem with X10 communications.  This document will cover some background, and how we can maintain reliable X10 communications when using CFLs.

Being concerned about energy efficiency, we began using CFLs back in the mid-90's.  We started with two brands – Philips “Earthlights” and a larger Lights of America unit with a replaceable bulb.  Both were expensive compared with today’s typical CFL.

The Earthlights work perfectly on X10 lamp modules, and could even be dimmed to about half intensity before they finally blinked off.  We still have some of those Philips Earthlights in daily service after a decade of use.  One has started to flicker when first turned on, and is probably nearing the end of its service life.  A downside of the Philips Earthlight is that it takes several minutes after turn-on before it reaches its maximum light output.

The Lights of America did immediately turn on at maximum intensity.  However, it was not X10 friendly.  That particular bulb had a large base that could be snapped open.  Inside there was a bypass capacitor directly across the AC power input, which effectively shunted the X10 signal on that circuit to ground.  There was room inside the base to add a 1000uH Miller “Hash Choke” in series with the center contact to block attenuation of the X10 signal.  The Lights of America CFLs were not dimmable, but they worked well with X10 appliance modules after the modification.  The light output of those Lights of America CFLs gradually decreased, and they were eventually replaced after several years of daily service.  While the bulb itself is replaceable, at current prices that costs more than buying a whole new CFL.

In this house we use CFLs for many of the ceiling cans.  I was aware of the possible problems caused by certain brands of CFLs, and installed a small Leviton 6287 in-line filter for every set of ceiling cans controlled by a X10 switch.  Any kind of incandescent or CFL can be used in those fixtures.  Even with the larger number of CFLs in this house, X10 communications has been virtually 100% reliable.

Below is a photograph of a X10 signal coming from a remote RR501 in the presence of background noise.  This noise was coming in over the powerline – perhaps from a wireless intercom or baby monitor at a neighboring house.  The X10 signal is about 400mVpp.  Note that the background noise level is about 100mVpp, which is why reliability problems begin to crop up when X10 signals degrade down to that level.


X10 Signal + Background Line Noise

The CFLs in my workshop are not controlled by a X10 switch, and I did not isolate them with a Leviton 6287 filter.  Those CFLs are “no name” units that were purchased at deep discount through the utility company.  While working on the XTB-II AGC loop, I discovered how difficult it can be deal with noise generated by some compact fluorescent bulbs.  The photograph below shows the signal received after passing through the bandpass filter in the XTB-II.  The 60Hz AC waveform has been removed, and this is the signal that is sent on to the envelope detector for decoding X10 signals.  The XTB-II bandpass filter is not high-Q to prevent too much ringing, but it does attenuate out-of-band signals.


Noise from 4 CFLs Beating Together

This testing was done in my workshop, which is on a non-X10 circuit powered through an Arc-Fault breaker.  Zero crossings are at dead center of the trace, and 8.3mS on either side.  The transient in center X10 reception window is on our powerline at all times, and is not related to the noise created by the CFLs.  As you can see, these particular CF bulbs generate a burst of noise centered around each zero crossing.  That is exactly when Insteon and X10 signals are transmitted.

To further complicate matters, the noise varies in amplitude from cycle to cycle.  This “pulsation” is apparently due to the high frequency choppers in the various bulbs running at slightly different frequencies.  As the noise produced by the choppers beats together, it can either sum to produce a stronger net signal, or cancel each other out.  As the noise pulsates, I measured up to 800mVpp, which lighted up two solid bars on the ESM1.  Note that in the above photo, the strong noise burst on the far right is square in the middle of a X10 reception window in the prior photo.  So, that would likely have been detected as a logic “1” by any X10 modules that received it.  I did confirm the noise pulsation is due to beating between the bulbs by removing all but one.  The CF bulb causing this havoc is the TCP ESN18.

One of the reasons this noise is particularly difficult to deal with is that it does pulsate.  So a module with AGC can sample the background noise near a null, and the noise can rise to a peak in the middle of a X10 reception window.  In fact I saw extra "1"s received when that happened.  It resulted in a reported collision, and a rejected message.

These particular CFLs have a relatively small base so they will fit into most light fixtures.  There is not much room for the high-frequency chopper that produces the electromagnetic field that lights the bulb.  While I have not disassembled one to confirm, I suspect there is insufficient room for an electrolytic filter capacitor, and rectified line voltage is supplied directly to the high-frequency chopper.  That could cause its frequency to vary throughout each half cycle of the 60Hz waveform.  It so happens that the chopper frequency of these particular CFLs falls into the 120KHz X10 bandpass as the line voltage approaches zero, which is when X10 signals are transmitted.  Higher frequency noise in the middle of each half cycle was rejected by the XTB-II bandpass filter.

The bottom line is that certain compact fluorescent lights can cause problems for X10 signal transmissions.  If you use CFLs, and have X10 reliability problems, it may be necessary to isolate some of them with filters.  The easiest approach is to use a X10 signal meter that can also monitor line noise, such as the Elk ESM1.  Unplug or switch off all CFLs.  Then reconnect them one-by-one while monitoring the background noise.  Any time the background noise level increases when a CFL is switched on, that bulb should be isolated by a filter, such as the plug-in XPPF or the wire-in Leviton 6287.  Since some CFLs can also be a “Signal Sucker”, it is wise to also check X10 signal levels as each light is reconnected.

If you are handy, an inexpensive solution for many table lamps is to install a 1000uH Miller 5258-RC "Hash Choke" in series with the hot lead.  Double insulate it with shrink sleeving.  While the 1000uH inductor is rated 1 amp (100 watt bulb), I recommend the higher current 250uH 5254-RC if you will ever use a high-wattage incandescent bulb in that lamp.  Electronic supply houses such as Digikey and Mouser carry the chokes and suitable shrink sleeving.

As we install more and more compact fluorescent lights in our homes, it is advisable to spend some time and effort as a precautionary measure to keep our X10 systems running perfectly.

I hope sharing my experience in these tutorials will help others obtain the same level of reliability that we have here.  X10 has been with us for 3 decades.  Its low cost and rich selection of devices still makes it a cost-effective solution.  Installations today can certainly be more challenging than they were decades ago, but investing some time and effort up front will give a big payoff in the years to come.


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