Re: Dumb question ...

Sounds to me that the lamp is going to try to get its 10 Amps and will blow
up the transformer.
George


"Daniel" <dxmm@xxxxxxxxxxxxxxxxxx> wrote in message
news:465fe984$0$16345$88260bb3@xxxxxxxxxxxxxxxxxxxx
Watts is Power measure in DC circuits where as VA is power measurement
(sort of) in AC circuits because of possible phase shifts between the
applied voltage and the Current.

If, and that's a very big IF, the circuit is PURELY resistive, the the AC
Power will be the same as the VA rating.

40 VA transformer can, usually, very easily drive a 250 W lamp, but the
lamp will, most likely, be fairly dim.

Daniel


George wrote:
...In other words, VA is the power rating, similar to saying 40 Watts.
So a 40VA transformer cannot drive a 250W lamp.


"Daniel" <dxmm@xxxxxxxxxxxxxxxxxx> wrote in message
news:465d5249$0$13928$88260bb3@xxxxxxxxxxxxxxxxxxxx
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

--
Posted via a free Usenet account from http://www.teranews.com




--
Posted via a free Usenet account from http://www.teranews.com



.

Relevant Pages

  • Re: Underwater light (update)
    ... Household circuits are not 30 amps. ... In the event some licensed electrician does ... circuit breaker and things may be just fine. ...
    (rec.ponds)
  • Re: Buzz box output voltage?
    ... The welders secondary circuit is a coil. ... are called for by a welder to move about - these are inductive by nature. ... The current flowing in the transformer when there isn't a current flowing ... around 28 amps. ...
    (sci.engr.joining.welding)
  • Re: Underwater light (update)
    ... Household circuits are not 30 amps. ... In the event some licensed electrician does ... circuit breaker and things may be just fine. ...
    (rec.ponds)
  • Re: Double Pole Circuit Breakers
    ... I am drawing ten amps! ... Each lamp gets 12V at 10A. ... load calculation only. ... An Edison circuit is just a 240 volt circuit with a grounded ...
    (alt.home.repair)
  • Re: Newbie: Series/Parallel DC circuit current question
    ... I can't draw the circuit so I'll ... 100v/50ohms = 2 Amps ... enters a junction, the same value must leave the junction. ... being shared by three equally valued resistors in parallel, ...
    (sci.electronics.basics)