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

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
>
>