Re: 24VAC power supply

[Matt Ion <soundy106@xxxxxxxxx>]

On 11/11/2009 5:02 AM, nick markowitz wrote:
> On Nov 11, 4:44 am, 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.  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.
>
> 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.

This is true too.