Re: [CAD_CAM_EDM_DRO] 470/100 caps (was Suitable Cap for Gecko's was Re: 8-wire 1/2coil stepper?

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 ?

No, it does more. It absorbs energy 'reflected' off the stepper motor,
and bouncing around the wiring. The very fast rise and fall times of
the currents in the power FETs in the Gecko drives can cause large
voltage transients on the DC power bus into the Gecko. There wasn't
enough space in the box for a sufficient capacitor, so it has to be
outside. If left out, and the main DC capacitor bank is too far away,
wiring inductance allows the voltage at the input terminals of the
Gecko to fluctuate wildly, enough to damage components.

> 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?

The on-board regulator was never designed to handle voltages that
change at 100 Volts / microsecond, which is possible in some cases,
without the external cap.

The real reason for higher-grade caps is for lower "ESR" (Equivalent
Series Resistance) which helps keep the voltage swings under tighter
control. Leakage current isn't a big consideration, here.

Jon