Re: [CAD_CAM_EDM_DRO] Re: Just an idea

Mariss Freimanis wrote:

> Carlos,
>
> Thank you for the kind words and will do. The problem with caps is
> energy density, i.e. how many watt-hours can be stored per unit
> volume. Doing violence to a differential equation yeilds:
>
> C = I dt / dv
>
> If I is 25 Amps, dt is 1 second and dv is 2.5 volts (10% drop on a 25
> VDC charged cap), then C equals 10 farads or 10,000,000 microfarads.
> Figuring an energy density of 3000 uF @ 25VDC per cubic inch (Al,
> lytic) results in a capacitor volume of 3,333 cu-in or, a cube 15
> inches on a side. Possible but not practical. Can you imagine the
> BANG it would make if you reversed the polarity though...?

Delivering 25 Amps for 1 second to a big servo motor would send the
table
right off the machine, or topple the whole thing over! I literally was
worried
once, in the early days of learning the art of servo tuning, when I
caused an
oscillation, and the whole Bridgeport started rocking! I hit e-stop,
because
if the amplitude built up much more, the machine would have tipped over.

My servo system has the X and Y axes set for about 5-6 A max, and the
amps
won't deliver more than that. Also, unless this current is needed at
high
velocity, the power supply draw is less, because these amps use a
switching
technology. Usually these currents are seen at the beginning of a move,
where
the output current is high, and the voltage is low, because the motor is
not
turning fast at that point. Therefore, the current drawn from the power
supply
is much less than the motor current.

I have a DC supply with two ~ 80,000 uF caps in parallel. At one time I
had
disconnected one of the caps. While working on it, I managed to bump
the
connection so the two caps were back in parallel, and the bang it made
as energy equalized between the two caps sounded like a gunshot
(indoors,
which it was)! I wouldn't want to play with a 10F cap at 80 V!
Although, they
are starting to make supercapacitors for electric vehicle energy
storage, and
they would be bigger than this.

Jon