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

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

Reply to
Andrew(N)
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You may save a little going with a more efficient power supply, but it won't be significant because you aren't making any changes to the field devices that draw the bulk of your power. Reducing the size of the transformer won't affect things much either (the smaller one will tend to run even hotter). Where the "savings" will come in is the efficiencies gained in the charging circuit for the stand-by battery, but that's about all I see as any real benefit.

In the future I would suggest posting a question like this in each group individually (and avoid cross-posting). That way if the thread "disintegrates into flame wars" in one group it won't affect the other.

Frank Olson

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Reply to
Frank Olson

I took your $56/month and divided it by $0.11/kwh (all inclusive sample cost out of your pocket) = 509 kW/month divided by 24hrs divided by 31 days = 684 Watt continuous load. This sounds very high. You would have 2,330 BTU/hr of heat assuming all this energy was used within your closet. It would be very warm/hot without proper ventilation. This figure does not sound right for what you are describing.

A linear power supply is most efficient when near fully loaded. The transformer core magnetization current is constant no matter what the load. A switch mode supply is more forgiving when lightly loaded.

As others have stated, check the theory on the difference between VA and W. You are *not* paying for V x A on the AC side. You are paying for WATTS only. Or measure and calculate V x A on the DC side and multiply by 1.25 for the power supply efficiency to reflect an approximate cost on the AC side. A good switch mode supply should be 87 to 94% efficient while consumer grade switchers will be slightly less (~77%).

Charging a small battery (10 AHr) isn't usually a big deal. The float current is sufficiently small (10 to 20 mA = .28W worst case).

Turning off unnecessary parasitic loads will have a more significant impact.

Good luck.

Reply to
RoughRider

There are always tradeoffs in design considerations. May I suggest thinking about it another way....

For an alarm power supply, normally wouldn't you want that to be a mission critical application... In other words (you want it to keep functioning, no matter what). If that costs you more in terms of kWh consumed, perhaps the price is worth it.

In my experience, some of these small plug in switching dc supplies are more prone to failure when compared to a good, well designed (or over-designed) linear supply. Generally they a pain to fix and it's usually more convenient to replace the whole supply when it goes down.

True, they are small, cheap, and efficient, but unless they are designed really well (adaquate cooling & heat sinks, plus fans if necessary), switching supplies generally operate with certain components under stress (capacitors and the critical transistors) , and again, in my experience, sometimes they just stop working. YMMV.

Beachcomber

Reply to
Beachcomber

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