Re: 24VAC power supply

[nick markowitz <nmarkowitz@xxxxxxxxx>]

On Nov 11, 4:44=A0am, Matt Ion <soundy...@xxxxxxxxx> wrote:
> On 10/11/2009 11:30 PM, Christopher Glaeser wrote:
>
> > The Altronix ALTV244175ULCB Power Supply can be configured for 24VAC or
> > 28VAC. =A0However, when configured for 24VAC, a DVM indicates 27.8VAC a=
t the
> > power supply. =A0If the specifications in the manual for a security dev=
ice
> > are, for example, 22VAC to 26VAC, would you expect 27.8VAC (assume
> > relatively short run with minimal voltage drop) to work fine?
>
> Unless your meter reads "True RMS" (a function normally relegated only
> to upper-mid-range and better devices), you're probably getting a
> reading somewhere between RMS and peak-to-peak, whereas device voltage
> ratings are generally rated as "VAC RMS". =A024VAC RMS is actually about
> 34V p-p.
>
> Remember that your output voltage with a straight transformer will vary
> proportionally with the input voltage: if you have a 5:1 transformer,
> 120VAC input will give you 24VAC output, but 130VAC input will give you
> 26VAC out, and 110VAC in will give you 22VAC out. =A0Since line voltage
> can often vary by 5% or more, expect your output voltage to vary
> accordingly.

As as you put a load on a transformer the voltage will drop also what
your reading is voltage at no load..
which is always a litle higher.