Re: Power Supplies, Saving Money, and switching vs. Linear?

[nobody@xxxxxxxxxxxx (Dave Houston)]

How did you determine the cost? How are you measuring the power? 12V and .5A
is 6W. I doubt that your transformer is really wasting 126W as heat. Does it
get as hot as a 125W light bulb?

I suspect a wattmeter (e.g. Kill A Watt) will show a watt reading on the
primary that comes much closer to the calculated value for the secondary.

I don't have any large linear supplies but a 12VAC/500mA transformer I have
on an ESM1 shows 50mA on the primary (6VA) but only 2W using the wattmeter
mode. In Power Factor mode the reading is 0.36 which is in pretty close
agreement with the VA and W readings. The transformer presents an inductive
load so the voltage and current are not in phase.

"Andrew(N)" <andrew.ward@xxxxxxxxx> wrote:

>My electronics/wiring closet is costing $56/month to run. Ouch. Too
>much! So one-by-one I am changing things to be more power-conscious.
>
>Starting with a big linear 12V power supply. Altronics 12V, 4A type
>linear power supply with battery backup: standard for alarms (a few
>years back). I currently draw about 500 ma continuously, (Not sure what
>my peaks are, but bells and sirens are powered separately.
>
>This draws around 1.1 A on the AC line, so 132 Watts continuously. Big
>transformer, always warm. Seems wasteful.
>
>IF I SWITCH TO A NEWER, SWITCHING POWER SUPPLY, say the Elk P412 (or
>any other you recommend) WOULD I DRAW MEASURABLY LESS AC CURRENT?
>
>I am powering various motion detectors,  InfraRed repeaters (Niles), a
>small, 7 Watt audio amplifier and a few other devices.  Would the 100
>MV ripple on the Elk power supply bring any problematic noise along
>with it?
>
>Thanks for your suggestions
>
>-Andrew