RE: [CAD_CAM_EDM_DRO] Variable Transformer

Jon:

That makes sense to me at first glance. I won't say I completely understand
it yet, but it gives me a direction to go in.

Thanks for the offer of the picture, but I think I will draw my own
instead-that's pretty much my standard way of explaining things to
myself(and to others) If you sent me a picture, I would just have to redraw
it anyway!

Thanks for the info.

Andy Wander
Verrex Corporation

-----Original Message-----
From: Jon Elson [mailto:elson@...]
Sent: Wednesday, June 29, 2005 9:39 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Variable Transformer

Andy Wander wrote:

>Jon:
>
>Thanks, this is very interesting.
>
>Can you tell me why there is an AC component across the cap when the "-" is
>not grounded, and not when it is? I have seeen this, but am not sure why it
>happens.
>
>

If you use a variac directly from the power mains to a bridge rectifier,
no terminal
of the capacitor can be grounded. During the negative cycle of the
power mains
hot lead, the minus side of the cap will be essentially connected to the
hot wire,
so obviously you can't ground this.

There isn't (much) AC voltage ACROSS the CAP, but the cap floats between the
negative peak and positive peak of the mains voltage, depending on the cycle
of the AC voltage at that moment. When the line voltage is near the +
or - peak,
then both cap terminals are connected to the mains by two of the diodes
becoming
forward biased, and the cap receives current from the line. This is
real hard to describe
in words. I could draw a couple of pictures that would explain it
pretty well.

Jon



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