[NCLUG] Experiences with x10 home automation system?

[John L. Bass]

	The appliance modules sound as if they might use relays, but none of the specs 
	on the x10 site make sense to me. To cite an example, I couldn't figure out 
	why the appliance modules are rated at 15 amps but only 500 watts, while the 
	SR227 wall-mount outlet is also rated at 15 amps but 1800 watts. They both 
	operate at 110V, and can carry the same amperage, so why does the wattage 
	differ? As far as I know, P = IV still holds in this part of the universe and 
	both should be able to handle 1650 watts.

	Marcio Luis Teixeira

The lamp modules are designed for normal light bulbs - which are nearly purely
resistive and P=IV does apply. Lamps also have a very short surge current on
turn-on - the resistance is proportional to the lamp temp, which rapidly goes
up as it turns on and produces light (normally within 1/15th sec). The lamp modules
are marginally useful for controlling other loads - I suspect because they still
have a "TRIAC" switch in the design (at least the early ones 20 years ago did).

The appliance modules are designed to switch highly inductive motors which have
a serious phase angle shift between voltage and current, as well as huge startup
currents which typically last the better part of a second or two. P=IV does not
apply to capactive and inductive loads, each of which seriously shift the peak
current in relationship to voltage. With inductive loads V leads I by up to 90 degrees,
and with capactive loads I leads V by up to 90 degrees (from 101 engineering class
in college).  There is a term called "power factor correction" where these type of
loads are augmented with the other to cancel out the phase shift.

Power factor correction is a serious issue for devices feeding switching computer
supplies, since the present a large capacitor to the line (behind a full wave bridge
rectifier) - or the device must be seriously derated.

Have fun,
John