470/100 caps (was Suitable Cap for Gecko's

Hi Dave,

You'd have to ask Mariss for more detail, but from what I've read in
Mariss' white papers, I believe the cap is to supply the 20Khz current
pulses from the drives. This cap serves as a "flywheel". The flywheel
is not as effective if the circuit must go back to the main power supply
cap through long (18") leads. The Fuse it seems also contributes to
increase the series inductance/resistance of the power supply circuit.
I seem to remember a "low ESR" cap being specified for this, although I
didn't find a reference.

Mariss has recently stated that the cap also helps to limit the power
supply voltage, especially if operating near 80v (and high current), as
I recall.

I don't think the internal "logic" is affected by this cap. This is a
"motor" cap. The logic circuits take 5V. We want to keep the motor
voltage separate from the logic voltage! ;>)

Yeah, I really think I'm gonna add some local caps!

Alan KM6VV


turbulatordude wrote:

>
> Hi Alan,
>
> I assumed that the cap on the power input to the Gecko was just to
> stop the current/voltage from dropping due to the output and distance
> from the power supply.
>
> if that is all it is doing, then won't just about any style cap do ?
>
> I know very little about the differences, but thought the lower
> leakage offered benefits to microprocessors and analogue measurement
> and circuits that measured voltage. Doesn't the Gecko have an on-
> board voltage regulator so once the power is applied, it has to drop
> to like 7 volts before logic circuits start to get bored and stop
> working?
>
> Dave
>
> --- In CAD_CAM_EDM_DRO@y..., Alan Marconett KM6VV <KM6VV@a...> wrote:
> > Hi Dave,
> >
> > Thanks, I did something similar. Only I looked for low-leakage
> caps. I
> > think we want a better cap then a cheap electrolytic (Tantalum low
> > ESR's, I think). I couldn't remember the "low ESR" last time I
> posted.
> > All I found were 6v caps. Otherwise, I'd have a bag of 'em!
> >
> > Alan KM6VV