CAP's (once again) (was Re: another transformer question

Do not use a diode; that is asking for trouble! The returned energy
is in the form of a current. It will happily charge the little 470uF
cap way beyond the 80VDC limit. The diode prevents the much larger
filter capacitor from helping, along with the other drives that would
act as a load to this current.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "caudlet" <tom@t...> wrote:
> --- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:
> > Dave,
> >
> > They still are aluminum electrolytics. Low ESR simply means
> > low "equivalent series resistance". The bigger the cap (uF), the
> > lower the ESR. One thing I forgot to ask; what is your power
supply
> > voltage and what was the voltage rating of the cap that blew?
> >
> > Mariss
>
>
> Mariss: What have you seen in back EMF from motors under load? Is
> it possible that voltage coming back might be charging the smaller
> caps past their WVDC rating? What about negative spikes? Using a
> low ESR cap will help absorb some of the higher frequencies but its
> only as good as the ground you put on the ground lug. Most of the
low
> ESR caps I see now are three leads. Some of the controller
> units/power supplies I have seen have intergal overvoltage
protection
> using the old voltage sensing power transistor to turn on a power
> resistor to ground.
>
> I diode isolated the last unit I did so that each motor had its own
> isolated leg and could not shove voltage back into the main buss. I
> put smaller caps on the anode side of the diodes to provide
> additional isolation.