Re: What size capacitor should I use?

Ok...10 amp power supply with 5600uf cap...Vishay makes a 5600 in a
36DY type it is rated for a ripple current of 10.66Amps...If this is
the cap you have, you are right on the bleeding edge of the
spec...And that is assuming you used a computer grade cap with a high
ripple rating...If not you are way over the current limit...

But i suspect this is not your complete problem...With such low
capacitance you have little capacity for the instantaneous power
required for pwm drives...If you look at your waveform on the scope i
suspect you will see the begining edge at one level and the trailing
edge at a lower level...You are not delivering max power to the
load...Your wavform will look worse and worse with each motor
running...

Wally

--- In CAD_CAM_EDM_DRO@yahoogroups.com, erie <erie@s...> wrote:
> As a general rule, I use several smaller caps in a bank, with bus
bars.
> Why? well like most everyone else
> here, I have to scrounge, I have a supplier that has 10,000 uf 150v
caps
> and cases of them, at a fair price.
> I usually buy 50 or so at a crack, and when I'm getting low, order
more.
> 66% of max load is conservative,
> heck, I've got a 60 v 10A ps on my router right now, with 5600 uf
> capacitance, by the numbers waaay to small,
> yet scoping the rails during operation shows less than 1v p-p
ripple,
> with 3 201's set at 5.5A each. For a customers machine, it would
> probably have 20,000 uf or so, but I haven't seen any issues here
yet.
> As usual, YMMV.
>
> erie
>
> caudlet wrote:
>
> >--- In CAD_CAM_EDM_DRO@yahoogroups.com, Andy Wander <awander@v...>
> >wrote:
> >
> >
> >>Dave:
> >>
> >>The OP asked if he needed to do this "per drive, so that is where
> >>
> >>
> >the
> >
> >
> >>multiple power supplies came from.
> >>
> >>Several of us have commented that multiple caps will work just
> >>
> >>
> >fine; one
> >
> >
> >>person did say multiple caps in parallel would be better; I am
not
> >>
> >>
> >sure why
> >
> >
> >>that would be, but I am not prepared to dismiss it out of hand
> >>
> >>
> >without
> >
> >
> >>hearing the reasons why it might be better.
> >>
> >>Andy Wander
> >>Verrex Corporation
> >>
> >>
> >>
> >>
> >There are two reasons to parallel caps (well actually three).
Cost.
> >In our world of scrounged parts it's ususally easy to find caps at
> >the voltage required at smaller values. When you start looking
for a
> >35,000 to 80,000 mfd cap with a 100 volt rating they get more
scarce
> >($$$$). Next is the physical size. Smaller value caps are
typically
> >shorter and have less cross section per MFD so three 15,000 100VDC
> >caps will probably end up being somewhat smaller in total. The
last
> >thing is ESR (Effective Series Resistance). All caps have
> >capacitance (duh), resistance and inductance. The larger the cap
the
> >more ESR it has. Take 3 smaller caps in parallel each have
smaller
> >ESR each and in parallel they have 1/3 the ESR of one. ESR in
linear
> >DC power supplies is of little concern since it would limit the
> >ability to filter higher frequency waveforms but are used
extensively
> >in switchers as filters. Besides, I wanted to give everyone
> >something else to stew about (:-)
> >
> >Oversizing the power supply for the load offers no tangable
benefits
> >other than making the builder feel better. I think even the 66%
> >number is conservative. I find in the actual world the total
worst
> >case current draw (all motors under normal load) is closer to 50%
of
> >the nameplate values on a chopper system.
> >
> >Watts is watts. The average current is a factor of the
instantaneous
> >current times the duty cycle.
> >
> >
> >
> >
> >
> >Addresses:
> >FAQ: http://www.ktmarketing.com/faq.html
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