Re: Water heater eating X-10 signal

["Jeff Volp" <JeffVolp@xxxxxxx>]

"Dan Lanciani" <ddl@danlan.*com> wrote in message
news:1338641@xxxxxxxxxxxxxxxxxxxxxx
> In article <84yVh.56915$VU4.35719@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
> JeffVolp@xxxxxxx (Jeff Volp) writes:
>
> | Many houses have 240V high-current resistive heating loads (ranges and
> | dryers).  The inductance of those circuits would be relatively low, so
> the
> | effect may be more significant than a variety of 120V loads that sum up
> to
> | the same current.
>
> Just to clarify something:  when you talk about the effect of 240V loads
> is the concern that they lower the impedance of the whole network as
> seen at the repeater significantly compared to the impedance of the
> repeater's drivers such that you can observe a lower carrier level at
> the repeater itself?

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.  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.

> | At first I thought you had a point here, but remember that each neutral
> goes
> | back to the distribution panel common bus.  It doesn't make any
> difference
> | on each of the 120V circuits what the phase is because there is no
> summing
> | together of the return signals on a common netural.
>
> You are ignoring multi-wire branch circuits and sub-panels (themselves
> essentially big multi-wire branch circuits).  I don't know whether this
> is a reasonable simplification to make in general, but it would almost
> certainly not be appropriate for my house which has more than its share
> of both.

By multi-wire branch circuits, you are referring to 120V circuits fed off
both legs with a common neutral.  Yes, the X10 signals would sum on that
common.  I suppose it would be possible that each leg might have several X10
loads, but I think that is reaching pretty hard to find something that might
have a problem.

I did not consider multiple sub-panels.  It would be intersting to find out
how much signal is lost in the heavy cable run between sub-panels.

> | Of course, that assumes
> | the transmitter is relatively close to the distrbution panel so the
> summed
> | return signals in its own neutral can be ignored.
>
> As long as we are assuming that, it would probably also be reasonable to
> assume that we can ignore any loss in the repeater's hot leg connections
> along with any losses in the single panel's bus bars, breakers, etc.  With
> this model, it appears that the only way a load on one circuit can affect
> the signal level on another circuit is by driving the level down at the
> repeater itself by presenting a relatively low impedance compared to that
> of the repeater's drivers.  This conclusion seems to conflict with my
> observations where the level at a repeater can remain constant (high)
> while switching a given circuit in and out changes the level seen on
> another circuit.  This makes me worry that the model is now _too_
> simple. :(

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.  With only a couple of feet of wire between the XTB-II and the panel,
the levels were the same at the XTB-II and inside the panel itself.  While I
don't have measurements to back it up, I would expect that switching off all
breakers on either leg would increase the level on that bus back to 40Vpp.

> N.B. I'm still very interested in the possibility of a repeater that
> drives the legs in phase (especially for use where a blocker/coupler
> is required) as I mentioned the last time this topic came up over a
> year ago:
>
> http://groups.google.com/group/comp.home.automation/msg/c638afa65ef96d86

Now that I've finally finished with my tax return, I've started back on the
enhanced repeater version of the XTB-II.  That will drive both legs in
phase.

BTW, thanks for the info on the stove/dryer receptacles.  I had thought the
3rd prong was ground.

Jeff