Re: Water heater eating X-10 signal

[ddl@danlan.*com (Dan Lanciani)]

In article <9bDVh.325907$5j1.101315@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>, JeffVolp@xxxxxxx (Jeff Volp) writes:

| I'm not sure I understand your question.  I think a low-impedance 240V
| resistive load with relatively low inductance can act as a "super signal
| sucker" if the two legs are driven out of phase at 120KHz.

Often when referring to "signal suckers" people are talking about local
loads that effectively form a voltage divider in combination with the
line back to the transmitter (repeater, whatever).  Usually the transmitter
itself is not noticeably loaded.  Under the simplified model we discussed a
240V load on a dedicated circuit would pretty much have to impair the
signal at the transmitter to cause a problem.

| I would expect
| some decrease in signal level at the repeater when confronted with such a
| load, especially if that repeater has a transformerless power supply.

So you are thinking that even though the repeater's driver might have an
impedance in the fractional ohms there isn't enough power available
from the supply to maintain voltage?  That might be reasonably easy to
instrument directly with a meter on the supply rail of my spare/repaired
CR230 (which uses the typical reactive power supply).

| By multi-wire branch circuits, you are referring to 120V circuits fed off
| both legs with a common neutral.

Yes, also knows as Edison circuits.

| Yes, the X10 signals would sum on that
| common.  I suppose it would be possible that each leg might have several X10
| loads,

It's not just X10 loads; it's any loads.  And it doesn't take more than
one per leg, though obviously for this to be meaningful in the case of
one load per leg at least one load has to be interested in hearing X10.

| but I think that is reaching pretty hard to find something that might
| have a problem.

I'm not looking for a problem; I'm looking for pros of each approach.  I
probably should not have phrased it in terms of giving something up.  So
far, out-of-phase drive appears to offer 240V module compatibility and
the ability to take advantage of shared neutral configurations in much
the same way the power distribution system itself does.  In-phase drive
allows you to use a smaller power supply and/or higher impedance drivers
in the face of 240V loads and may offer better compatibility with in-phase
couplers.

These are all pretty minor features, and I'm not convinced that the problem
you fear from 240V loads is any more an issue in real life than the ability
to take advantage of multiwire branch circuits.  I brought it up only
because the original poster's fact pattern was unusual.  At least to me the
optimal choice is far from obvious and I would still be inclined to make it
an option if I were building a repeater product.

| Actually, here I saw the combined loads have a significant effect on the
| XTB-II output.  The XTB-II will output over 40Vpp with no load.  I measured
| one leg at 25Vpp, and the other leg at 30Vpp when it was connected to the
| panel.

Was this due to the output impedance of your drivers or a sagging power
supply?

				Dan Lanciani
				ddl@danlan.*com