Re: caps reversed

Hi Mariss,

Thanks for the description of what can be an interesting evening.
Fortunately the cap didn't explode or the "housekeeper" wil have lots
to say. Probably saved by the fuse. And to think that I had toyed
with the idea of leaving out the fuse for convenience.

And your hardy geckos still putting out nice red light after I
changed the fuse.

Thanks

andrew

--- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:
> Andrew,
>
> Reversing the polarity on an aluminum electrolytic capacitor
> depolarizes it. That means the ultra-thin coating of oxide
(isulator
> or dielectric) is de-plated and its insulating property disappears.
A
> large DC current begins to flow between the foil capacitor plates
and
> heats the electrolyte between them. The electrolyte fluid begins to
> boil, and that creates a pressure inside the aluminum can
sufficient
> to explosively rupture it should the safety vent not work.
>
> Or: Look at the size of the capacitor. It will explode like a
similar
> sized firecracker. There will be aluminum foil confetti all over
the
> place along with a really good spray of corrosive electrolyte all
> over the surrounding electronic circuitry. It is a mess to clean up
> but the "bang" is fun if you aren't expecting it. Hopefully the can
> will miss your face as it flies by at a few hundred feet per
second.
> Other than that, it's not a problem.
>
> Mariss
>
> --- In CAD_CAM_EDM_DRO@y..., "andrewyslee" <andrewlee@s...> wrote:
> > Hi,
> >
> > Just to remind those using G201 to check that the capacitors they
> put
> > on terminal 1 and 2. I may have blown 2 3Amp fuses because I had
> the
> > polarity on the z-axis reversed.
> >
> > When I switched on the driver, I noticed the LED on the z-axis
was
> > unlit. Thinking it might be the fuse, I switch fuses on the y-
axis
> > and the z-axis. Sure enough, the y-axis now is unlit, and the z-
> axis
> > LED light came on. But the joy was brief, as was the light. It
went
> > out after approx. 1-2 sec. On closer examination, I noticed that
> the
> > polarity of the 470uF was reversed.
> >
> > What is the effect of having the 470uF capacitor reversed?
> >
> > andrew