RE: [CAD_CAM_EDM_DRO] current rating of transformers

Yeah, but....

I still say that the thing that limits the secondary current is the wire
gauge used for the secondary winding.

I don't think many transformers are built using wire that's a lot heavier
than needing fro rated output current. Therefore, dropping the primary
voltage(thereby dropping the secondary voltage) doesn't mean you can now
pump more current through it to "get back" up to the VA rating.

Andy Wander
Verrex Corporation


-----Original Message-----
From: Jon Elson [mailto:elson@...]
Sent: Sunday, October 24, 2004 11:30 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] current rating of transformers


Andy Wander wrote:

>Jon:
>
>I could be wrong, but I think you're confusing transformer output with
>stepper input here...:)
>
>If I am correct, the current rating in a transformer has mostly to do with
>the gauge wire used, and if half the winding can take 10A, so can the full
>winding.
>
>

No, it is a bit more complex. If you use the 2-diode full-wave scheme
with the
center tap, each half of the winding draws current only every other
half-cycle,
thereby giving it a "rest" or reducing the duty cycle. Of course, you also
get half the voltage that way, compared to a full-wave bridge using the full
winding. That also explains why the transformers have VA ratings. If you
reduce the output voltage, you can get more current to equal the same V*A.

Also, the capacitor input filter draws current in pulses, which reduces
the rating
of the transformer further.

>
>

Jon