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

[not_real@xxxxxxx (Beachcomber)]

>
>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%).

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

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