Modification of X10 220V Heavy Duty Appliance module for use with 3
X10 home automation modules allow for control of a variety of
devices. X10 sells both 15 and 20 A "Heavy Duty" appliance
modules for controlling 220V appliances. My automation goal was
simple: I wished to turn on the air conditioner at my vacation
home before leaving, thus having it cool on my arrival. I have
only DSL with a wireless acess point there, so elaborate computer based
systems are out. I set up an X10 system with a Dataprobe
Web-X10 controller to allow for remote access. The Web-x10 provides
a simple web interface to control a CM-11a on site. A sonicwall TZ170 maintains the DSL
connection and a VPN connection to my other residence for secure remote
access, as well as providing wireless access when I am there.
When I plugged in the appliance module it didn't work. All
the other 120 V modules worked, and I tested the 220 volt module at my
other house and it worked there, so I knew it was not a defective
module. The electrical panel appeared to be split phase (not a
three phase panel) and the utility is billing me for "single phase"
service. As it turned out, the building had three phase service,
and it is well described that the 220 v appliance modules won't work
with a three phase system.
Further information about 3 phase
power and X10 can be found on Ido Bar-Tana's excellent page.
In order to understand why the module won't work on a three phase
circuit, it is necessary to review both how the X10 protocol works and
how a.c. power is delivered.
First X10: The
X10 protocol uses a 120kHz carrier over the power
lines and uses pulse code modulation timed with the zero crossing of
the a.c. power line. One bit is transmitted per power line
cycle. The X10 modules listen for the 120kHz signal when the zero
crossing is detected (the zero crossing is the brief
instant where the sine wave of the a.c. power crosses ground and there
is momentarily zero volts across the line). Modules can
therefore use the a.c. line to syncronize their reception of the
power line carrier. The approach works pretty well since an
entire home is supplied by the same line. American homes are
typically supplied with "split-phase" single phase power.
Basically the stepdown transformer is center tapped, with the center
tap grounded to form the neutral. Thus, there is 120 volts
between neutral and either pole, or 240 volts between the two "hot"
leads. The electrical panel usually alternates between the poles
to balance the load. 240 V appliances use both poles. The
X10 signal will not pass through the inductance of the utility
transformer. The problem is well described elsewhere and can be
resolved by putting a capacitor between the phases to couple the 120kHz
signal. The important point is
that both "hot" leads cross zero together. Thus where the two
phases cross corresponds with zero on both phases, and can be
used by the appliance module as a zero crossing reference (Figure 1 and
Three phase power:
Electricity is generated in three
phases (Figure 3). This provides both greater efficiency, and, if
phases are used, the current never drops to zero. To provide
split phase single phase power, the utility puts a center tapped
transformer on one of the three phases and sells you the output.
In order to keep the load balanced, a different phase is used to supply
the neighboring transformer. Typically one transformer supplies
several homes. Three phase power is also used. A three
phasee transformer can be wired as a "Wye" with the center
grounded, and supplies 120V on each phase. This can be supplied
to a three phase panel, and used to supply 120V single phase branch
circuits. A triple pole breaker can be used for 3-phase
appliances at 208V. A double pole breaker can be used to supply a
single phase 208V appliance by connecting it across two of the three
phases. The difference between the phases is less since they are
120 degrees out of phase. This is what the utility did in
my building (Figure 4). There are 12 apartments, each of which
phases. Each apartment gets two of the three, and it is wired so
each of the three goes to 8 apartments. Since X10 times the
pusle code modulation to the zero crossing and since the module
references the zero crossing to zero potential coming in through the
line, the zero crossing observed by the module will come at the wrong
time. X10 partially addressed 3 phase power by requiring that the
120kHz pulses be sent not only at the zero crossing, but also be
repeated at 2.778 and 5.556 miliiseconds (60 and 120 degrees) after the
zero crossing to cover the zero crossing of the second and third phase.
|Figure 1: One cycle of
split phase AC power. One phase is shown in red and the other in
black. Note that the phases are 180 degrees apart.
|Figure 2: Split phase AC
power. Note that both phases cross zero together, as marked by
the vertical red bars. The phases cross each other at zero.
In other words, when there is no potential difference between the
phases, there is also zero potential to ground as well. at 90 and
270 degrees, the difference between phases is at its maximum potential
(long green line) The short green marks indicate the timing of
X10 pulse transmission. The two pulses after the zero crossing
are designed to coincide with the zero crossing of the second and third
|Figure 3: 3 phase AC
power. Note the three phases are 120 degrees apart, and each
phase crosses zero independently. Because of this, three phase
power is more efficient since there is always voltage present.
With single phase power, current stops flowing briefly 120 times per
second during the zero crossing.
|Figure 4: Three phase
power as applied to the appliance module. For 208V three phase,
only two phases are used. The peak potential between the phases
(green line) is less than for single phase circuit since one phase (red
in this illustration has passed its peak while the other is approaching
it. Note that the zero crossings relative to baseline (pink line)
do not correspond to where the phases cross each other (thin vertical
red lines). The appiance module does not have a ground reference
(the pink line in this case), so the zero crossing detector detects
zero crossing when the phases cross.
|Figure 5: Three phase
power showing timing of X10 signals. Note that the X10 signals
are sent and correspond to the zero crossing of each of the three
phases. Note that at the crossing of any two phases (red bars,
and what is detected as zero by the 220V appliance module, no X10
signal is present). The designers thought about 3 phase
power, but didn't consider 208 V three phase, or they would have
transmitted 6 pulses per cycle, one every 30 degrees (1.389 ms).
With 50 Hz power, the problem is worse, since if a 60 Hz transmitter is
used, the second and third phase will be mistimed. It probably
would have been better if they just made the pulse last for the entire
half cycle. But they didn't.
So what are the options to deal with this problem:
The first three options require too much work, and would hamper use
with prewritten applications. Building in a delay would require
adding circuitry for which there isn't much room in the module.
So, the options are limited to the last two. I tested the module
by making an adapter to run it on 120 VAC. It works. One
could isolate the electrical supply to the module (except the power
detect line, which is isolated through a 330k ohm resistor) and power
the circuit from a 120 VAC outlet.
- Redesign the transmitter to send out extra pulses, or write
software to drive the PL513 or TW523 power line controllers properly.
- Place a 220V tranceiver module on the circuit between two of the
phases, possibly in a duplex receptacle with the appliance module (if a
transformer is used, a capacitor will be needed to couple the PLC
- Rewrite the firmware of the appliance module (probably
won't happen since there is a very small market)
- Build in a 1.389 ms delay into the zero detect line of the 78570
- Power the circuitry of the module using 120 VAC.
- Use ground as a phase reference for the zero detector.
But, a closer examination of the circuit reveals another option:
Note that D3 and D5 clamp the voltage between 0 and +15 V. Phase
one is applied to Vcc and is regulated to create logic ground.
The other phase is applied through R2. When the phases cross, a
transition occurs at pin 1 of R3 which is fed to the zero crossing
input of the 78570. Suppose we move pin 2 of R2 to neutral.
Then when the first phase crosses neutral, the zero crossing will be
detected. This is exactly what we want! But we don't have a
neutral wire in the module.
Ground and neutral are tied together in the main electrical panel, but
nowhere else (per NEC). Therefore, ground and neutral are electrically equivalent. The
reason it is against electric codes to use the ground wire as a current
carrying conductor is safety. If the integrity of the current
carrying ground were to be interrupted, say by a loose ground pin,
loose raceway, or loose ground wire, the outside of the appliance would
become electrified through the relatively low impedence of the
appliance. If a human were to touch it, most of the voltage would
be dropped across the relatively high impedence of the human body,
possibly causing electrocution. Fortunately, with 330k ohms,
there is a potential for only 0.4 mA of ground leakage. For
safety, a separate ground of the appliance using a cold water pipe
should be considered, especially if the appliance is a hot tub. A
ground fault circuit breaker should also be used. Most GFCI's
trip at 3-5 mA of ground leakage. If the modification is not done
correctly, there is an even higher potential for electrocution.
If a neutral wire is available in the box, or can be pulled (in the
case of conduit wiring), it should be used.
You can tell if you
have a three phase system by:
- Looking at the utility bill, electric meter, or circuit breaker
panel. If any indicate 3 phase service or show 3 hot lines coming
in, you have 3 phase service. But, as I indicated above, this
method is not foolproof. Use either of the three below for
- Inspect the blueprints for your building.
warning below) Carefully
Hooking a dual trace oscilloscope to a 220V outlet and observing the
phase relationship of the traces. Hook Y1 input to one blade, and the
Y2 input to the other. Compare to figures 1 and 4 above. Be
sure the 'scope can handle 120V RMS to
eash input. THE OUTSIDE OF THE OSCILLOSCOPE MAY
BECOME ELECTROFIED DURING THIS MEASUREMENT IF THE GROUND LEAD IS
CONNECTED TO THE OSCILLOSCOPE CASE. Consult an electrician
if you are not
absolutely comfortable with your equipment. I TAKE NO RESPONSIBILITY IF
YOUR ELECTROCUTE YOURSELF, BURN YOURSELF, RUIN YOUR EQUIPMENT, START A
FIRE OR DAMAGE YOUR WIRING. OR
warning below) Carefully
measure the voltage between each prong of the 220 V outlet and ground
using a voltmeter. Then measure the voltage between the two
prongs. If the voltage between the two prongs equals the sum of
the voltages measured on each pole, you have a split phase
system. If the voltage is about 15% LOWER than the sum of each
prong, you have a 3 phase system. THE OUTSIDE OF THE VOLTMETER MAY
BECOME ELECTROFIED DURING THIS MEASUREMENT IF THE GROUND LEAD IS CONNECTED TO THE
VOLTMETER CASE. I TAKE NO RESPONSIBILITY IF YOUR
ELECTROCUTE YOURSELF, BURN YOURSELF, RUIN YOUR EQUIPMENT, START A FIRE
OR DAMAGE YOUR WIRING. Consult
an electrician if you are not absolutely comfortable with your
equipment. A qualified electrician will be able to tell you if
you have a 3 phase circuit.
- Example: Voltage from left prong to
ground 122V, from right prong to ground 118V. Between prongs 239V
= Split phase system
- Example2: Voltage from left prong
to ground 122V, from right prong to ground 118V. Between prongs
210V = 3 phase system
WARNING: This information is
provided for educational purposes only. Any modifications to X10
modules are potentially EXTREMELY dangerous. You will void your
warranty and invalidate the CSA/UL listings by making
modifications. Additionally, there are hazardous voltages present
if plugged in with the case open that can cause DEATH BY ELECTROCUTION
OR SEVERE BURNS. Further, using the ground as a zero
reference exposes you to ground fault condition, if there is an open
ground, the outside of the controlled appliance could become
electrified AND CAUSE ELECTROCUTION. THE APPLIANCE SHOULD BE
INDEPENDENTLY GROUNDED TO ANOTHER SOURCE SUCH AS A METALLIC COLD WATER
PIPE. Miswiring may also result in FIRE or SMALL
EXPLOSION. PROCEED AT
YOUR OWN RISK. I take no responsibility for any untoward
consequences of using this information. Using the ground as zero
reference SHOULD result in no more than 0.4 mA of ground leakage IF
WIRED PROPERLY. It is up to the user to completely understand
what they are doing and the ramafications of this modification, and to
determine if the modification is suitable to their intended application.
|Figure 6: The outer
housing has been disassembled by removing the four
screws in the corner. The module acutally contains a wall outlet
module. I would assume this modification could also be used on
version of this unit.
|Figure 7: The receptacle
module itself is opened by removing the two screws on the back and
carefully sliding the cover down the power leads (red arrows). It
is not necessary to remove the circuit board for this
modification. Note the smaller black (upper left) white (lower
left) and blue (diagonal upper right to lower left) wires. These
provide power (each of the two input phases) through the black and
white, and power on detection through the blue. Functionally, the
white wire is the same as the neutral in 120 VAC applications.
(It is NOT neutral here)
|Figure 8: Identify the
330K (orange-orange-yellow) 1/2 watt resistor. This resistor
couples the zero crossing signal from the Line 2 ("neutral" in the
device schematics, actually the opposite phase of the input) to the IC.
|Figure 9: Cut the lead of
the 330K resistor as shown and remove the sleeving. Cut the lead
as close the the circuit board as possible.
|Figure 10: Solder a length
of wire to the cut end of the resistor lead. Place heat
shrink tube over the resistor and connection as shown. To bring
the lead out of the housing, you can either drill a hole in the back,
or bring it out through one of the unused corner holes. If you
use the corner holes, you'll have to make a notch at the inside to
allow the case to close all the way (area shown with arrows in Figure
2, but on the opposite side).
Once outside, the wire may be connected to the ground prong. You
can disconnect the connector and solder it on. If you are
mounting the module in a junction box as a receptacle, the wire
should be connected to "neutral." (the grounded conductor), and white wire
should be used.
That's it. Carefully reassemble the module being careful not to
pinch any wires. An ohmmeter check is recommended.
Measure the resistance between each blade of the plug and the round
prong. If either is less than 330,000 ohms, recheck your wiring
Plug the module into the 220V outlet without an appliance plugged
in. Send "ON" and "OFF" commands and listen for the click of the
module. If you don't hear it, go back and check your work.
It could also indicate a defective ground.
Not pictured: there is room in the housing to put a 0.1 MFD 600 V capacitor and 18 mH choke in series across the line to allow the module to also serve
as a phase coupler.