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

["Andrew(N)" <andrew.ward@xxxxxxxxx>]

Dave Houston wrote:

> 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?

The $56/month was by determined by using a WattsUpPRO wattmeter. and
multiplying KWH * Running time * Highest tier on my PG&E bill (corrected
for a monthly # of hours, of course). This was for the whole wiring closet.

I did not break into the specific AC circuit of that Altronics Power
supply with the watt meter. I have a Fluke T5 current probe. It's not
perfect, but gives an approximation.  It's not as hot as a 125'er, but
that's pretty subjective.  The linear regulator also generates some heat.

>
> 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.

OK... So I should probably break into the circuit and use the WattsSPpro
meter to get a good reading.

Still wondering if the switcher would save money power-wise.

Thanks Dave - As Always --- Everyone appreciates you.

-Andrew

>
> "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
>
>