Re: 24VAC power supply

[Matt Ion <soundy106@xxxxxxxxx>]

On 10/11/2009 11:30 PM, Christopher Glaeser wrote:
> The Altronix ALTV244175ULCB Power Supply can be configured for 24VAC or
> 28VAC.  However, when configured for 24VAC, a DVM indicates 27.8VAC at the
> power supply.  If the specifications in the manual for a security device
> 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".  24VAC 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.  Since line voltage
can often vary by 5% or more, expect your output voltage to vary
accordingly.