RE: [CAD_CAM_EDM_DRO] Re: What size capacitor should I use?

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


-----Original Message-----
From: turbulatordude [mailto:dave_mucha@...]
Sent: Wednesday, January 26, 2005 12:57 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: What size capacitor should I use?



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "A. G. Eckstein"
<a_eckstein@b...> wrote:

> Ron,
> I would base this on "per power supply". In other words if you have

1 power

> supply providing the necessary voltage/amps, then it would be one

(or more

> in parallel) to obtain the necessary capacitance. If you have 3

power

> supplies each rated at this voltage/amps, then yes you need 3 caps.
>
> The site that I mentioned earlier does not have a single cap rated

at

> 45KµF, so your best bet is as you have done and parallel the 3

15KµF caps

> which will give you the same total capacitance.
>

hunh ?????

70 volts, 12 amps. one power supply ?


"..So in your case, I would look at 80000*12/70 or 13,714µF and round
up to the next highest value with a voltage rating of at least
100V ...

Of course that is 80,000 for 60hz and 100,000 for 50 hz.


Where did multiple supplies and three times the power come from in
this thread ?


As Caudlet mentioned, most power supplies or way over sized for one
reason or another. Mine because I got the works complete and never
changed parts out.


But, for a Gecko, Mariss (the manufacturer) recomends sizing the
powr supply to about 66% of nameplate. So, one questions goes not
to power supply but motors. What is the total of the motors amps ?

If your power supply can handle 12 amps at 70 volts, but your motors
total 3 amps, then you need to take 60% of 3 amps (roughly 2 amps)
and then work the cap sizing by that. All the rest of the power
supply is 'reserve'


Also, there have been some recomendations on using multiple caps.
What is the reasoning behind that ? size ? effency ? cost ? some
other engineering reason ? or is that just a old wives tale ?

If the motors needs are 12 amps and the calculation shows 13kuF, and
a 15kuF is available, what possible benifit is gained by multiple
caps ?

Dave













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