Re: [CAD_CAM_EDM_DRO] capacitor

----- Original Message -----
From: "Jon Elson" <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, March 19, 2002 10:49 AM
Subject: Re: [CAD_CAM_EDM_DRO] capacitor


> Mike Snodgrass wrote:
>
> > Hello, I have a variac rated at 60A, and plan to rectify and
> > filter the current at my driver enclosure, to power my geckos. What
value of cap would I need? I realize it would
> > have to be rated at higher than required voltage. Also could I use a AC
cap ahead of the rectifier?
>
> This is extremely dangerous! A Variac is an autotransformer, and does not
> isolate the input from the output. You need to add a transformer of some
> sort to this, or the risk of electrocution or destruction of your computer
> and machine are very serious.
>
> Why on earth would you use a 60 A variac to power Geckos? The power
> loss in the Variac will likely be more than what is delivered to the
drives!
>
Hello Jon, The statement about the 60A variac is not set in stone. I also
have a 20A unit. The reason for the variac, was the higher voltage
capability. I had the larger
unit hooked into the input of my buzz box welder at one time, and after
going through the high-freq unit, I was able to tig weld thick foil. I
didn't think about the isolation
problem. I also had considered putting a scr chopping
circuit (retrieved from a welder) into the output , so as
current limit any type of driver I cared to use. Thanks for the advice and
the warning. Nothing sours a project quite
like being found dead at the throttle.




> An AC cap before the rectifier will serve no purpose. You need a
capacitor
> to maintain the DC voltage between pulses of the AC power line.
>
> Jon
>
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