to Low ESR or not to Low ESR, that is the ... ( was Re: GECKOS 201

Hi Jeff,

interesting article and the web page added a neat saying about the

"The reliability of any piece of electronics is inversely
proportional to the number of electrolytic capacitors in it"

I do understand the ESR, but the 470uF at the input on the Gecko is
there to filter the ripple from the drives, or rather from the motors
as they are switched off. The 470uF is there as a safety valve so to
speak and will not enhance or detract from the performance of the
Gecko or the power supply.

I just don't see any major benefits from a low ESR vs. a more common
cap.

Dave

--- In CAD_CAM_EDM_DRO@y..., "jeffalanp" <xylotex@h...> wrote:
> Hello,
> The following information was taken from the web site:
> http://www.mainelectronics.com/captester.htm
>
> About ESR...
>
> So what is an electrolytic's ESR?
> Electrolytics depend on a water-based electrolytic, soaked into a
> strip of porous material between the aluminum foil plates, to
> complete the outer electrical connection to the aluminum oxide
> dielectric coating on the anode foil.
> The electrolytic has electrical resistance which, along with the
> (negligible) resistance of the connecting leads and aluminum foil
> plates, forms the capacitors equivalent series resistance.
> Normally the ESR has a very low value, which stays that way for
many
> years unless the rubber seal is defective. Then the electrolytics
> water component gradually dries out and the ESR creeps up with
time.
> The electrolytic gradually acts more and more like a capacitor with
> it's own internal series resistor.
>
> Heat makes it worse...
>
> If an electrolytic is subjected to high temperatures, especially
from
> heat generated internally as a result of large ripple currents, the
> electrolytic will start to decompose and the dielectric may
> deteriorate and the ESR will increase far more rapidly.
> To make things worse, as the ESR increases, so does the internal
> heating caused by ripple current.This can lead to an upward spiral
in
> the capacitors core temperature, followed by complete failure -
> sometimes ever explosive!
> The service life of electrolytics is approximately halved for every
> 10 degrees C increase in temperature and, surprisingly, many are
only
> designed for a few thousand hours at their maximum rated
temperature
> and ripple current. (A year is 8766 hours!)
> Switch mode power supplies place quite severe stresses on filter
> capacitors. Because of their compact construction, temperatures are
> high and the capacitors have to endure large ripple currents.
>
> Hope that helps some
>
> Jeff
> www.xylotex.com
>
> --- In CAD_CAM_EDM_DRO@y..., "turbulatordude" <davemucha@j...>
wrote:
> > This pops up occasionally.
> >
> > LOW ESR or not for the 470 Caps. I have read more opinion that
> > engineering on this, and am still not exactly sure why the low
ESR
> is
> > desired.
> >
> > The availability between a simple alum electrolytic and a low ESR
> > make the alum much easier to get.
> >
> > Does the low ESR offer any substantial benefits ?
> >
> > Dave
> >
> >