Re: Dumb question ...

Jeff Strickland wrote:

"Rich Webb" <bbew.ar@xxxxxxxxxxxxxxxxxx> wrote in message news:gugp5392rv1fj1hgb7ccucfnd3j8ggv4iu@xxxxxxxxxx
On Tue, 29 May 2007 23:35:17 GMT, "Jeff Strickland"
<crwlr@xxxxxxxxxxx> wrote:

... mostly because I'm dumb.

What's the difference in a volt-amp and a "regular" amp?

I have a transformer that makes 24vAC, and is rated at 40 VA, but the amp
rating is only 1.67.

I have a lamp (fiber optic system) that takes 24v and 250W, which works out
to 10.4A. The VA rating does not give me the current I need, and when I plug
the light in, the voltage drops because the draw exceeds the power by a wide
margin.

http://en.wikipedia.org/wiki/Volt-amp is a starting point. To avoid
recapitulating what's explained better and in more detail elsewhere,
volt-amps and WATTS (not "'regular' amps") are the related
measurements.


Okay, so to distill it down, 40VA is not near enough to drive a 250w light?

Actually, this is a bit moot because another multi meter in my fleet has determined that the lamp is open. I can't explain why I couldn't figure this out before I bought the new power supply ...


Gee, that Wikipedia explanation is a bit hard to understand, so here is my attempt.

In D.C. circuits, the voltage peaks occur at the same time as the current peaks, so the power in the circuit is found by multiplying the voltage applied, i.e. if applying 6 volts causes 2.5 Amps to flow, the power dissipated by the circuit is (6 x 2.5) 15 watts.

However, in A.C. circuits, the effects of the components in the circuits can cause the peak current to not flow at the same time as the peak voltage occurs. So you may apply 6 volts a.c. to a circuit, and at some times 2.5 Amps a.c. may flow at some time, but because the 6 volts and 2.5 amps do not occur at the same time, it is, technically, incorrect to to same the power in the circuit is 15 watts, it is correct to say that the circuit draws 15 VA.

Daniel

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