Re: [CAD_CAM_EDM_DRO] Re: Sizing a power supply

Charles A Davis wrote:

> Hi Peter:
> Something that may be passing without really being noticed, "the
> isolation transformer" .
>
> This is a VERY important safety consideration. What I first noticed in
>
> this thread, was "buck-boost transformers". These may, or MAY NOT have
>
> isolated windings. In fact, a lot of 'buck-boost' devices are in fact
> 'auto transformers', which provide NO isolation.
>
> The main point of possibly deadliness, is that if you are not careful,
>
> you may end up with raw 110VAC directly connected to one of your
> 'stepper' power leads. Not affecting anything, until you inadvertently
>
> touch a finger or tool sometime.
>

Right, that's why I was careful to say what I said,

> Otherwise, you
> could use a 208/220 volt autotransformer in front of the isolation
> transformer to vary
> the output voltage.

but it bears emphasis to make sure that one of the transformers you
use has isolated windings. Test this with an ohmmeter, and you should
get infinite resistance from the wall plug terminals to the output
terminals. You generally can't make this test with AC and a DVM,
because the 10 Meg Ohm impedance of the DVM allows evan a tiny
capacitive coupling between the input and output windings to show
up as a significant voltage at the output.

Jon