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

Hi Alan,

I did a search on Digi-key for capacitors and a matrix came up. I
put in 470 and 100 volts and found caps of that value. they were
about $2.70 or so. (at least the one I found was)

Jameco lists electrolitic caps of 470uf/63v for $0.25 each in lots of
10, or 29 cents each for one. none of higer voltage.

Mouser lists the 470/100 for $1.98 on last years CD.

Dave

--- In CAD_CAM_EDM_DRO@y..., Alan Marconett KM6VV <KM6VV@a...> wrote:
> And Good afternoon to you too!
>
> OK, I think I get it now. Thanks for the further explanations.
> Actually not a bad thing, as the inductance effects are not as bad
that
> way!
>
> I hadn't thought of using my 'scope for inductance measurements.
Not
> since college!
>
> Alan KM6VV
>
>
> mariss92705 wrote:
> >
> > Alan,
> >
> > Good afternoon! A full step sequence is where A and B are the
> > windings, + and - is the "direction" of the current thru the
winding.
> >
> > +A +B, +A -B, -A -B, -A +B
> >
> > After this, the sequence repeats.
> >
> > For microstepping, pretend "A" is sine and "B" is cosine
magnitude.
> > Then "+" and "-" are the "signs" for the sine and cosine
functions.
> >
> > For the full step sequence (nothing more than a single-bit
> > approximation of the sine and cosine functions), the motor moves
1.8
> > degrees on each "sign" change. Being sine and cosine
approximations,
> > the sign changes occur every 90 "electrical" degrees. 360 degrees
in
> > a cycle, therefore 4 full steps per cycle.
> >
> > You can use a bridge to measure inductance but your reading will
be
> > high because it is taken at zero DC current. Magnetic saturation
> > effects (where you are on the B-H curve) will cause the working
> > inductance to be somewhat lower.
> >
> > I prefer to measure working inductance directly from the V/L slope
> > measured with a 'scope. Read the "delta I" over a "delta t"
period on
> > the 'scope. As an example, say you measure a 300mA change in
winding
> > current over a 12uS time span and you are using a 72VDC power
supply.
> >
> > The inductance will be 72V times 12uS / 300mA, or 2.88mH if the
slope
> > was linear.
> >
> > The cap is fine for power supply voltages up to 50VDC.
> >
> > Mariss
> >
> > --- In CAD_CAM_EDM_DRO@y..., Alan Marconett KM6VV <KM6VV@a...>
wrote:
> > > Hi Mariss,
> > >
> > > Very informative! Another "keeper"! Thanks for the
> > clarification. Why
> > > is it 4 steps/cycle? Seems like something is changing (a
current
> > > through a winding) EVERY step?
> > >
> > > I see a "Fl = 2 PI F L" inductive reactance calculation! Can I
> > measure
> > > the inductance of "unknown" stepper motors with an L/C meter
(kit)
> > such
> > > as:
> > >
> > > http://www.aade.com/lcmeter.htm
> > >
> > > I think the operating frequency is 1K. I don't have an HP4275A
> > digital
> > > L/C meter, or or a B&K 878 digital LCR meter!
> > >
> > > Also, is this 470uf cap suitable for the Gecko's (only 63v,
couldn't
> > > find higher)?
> > >
> > > P10351-ND EEU-FC1J471L CAP 470UF 63V ELECT FC RADIAL
Panasonic -
> > ECG
> > > 470µF 63V ±20%
> > >
> > > Found in DigiKey's catalog (only a quick online search).
> > >
> > > Alan KM6VV
> > >
> > >
> > > mariss92705 wrote:
> > > >
> > > > Hi,
> > > >
> > > > I think the thing being missed here full-stepping vs.
> > microstepping.
> > > >
> > > > If you have a 5V 1A per phase unipolar rated, 8-wire motor,
then
> > you
> > > > would run it at 1A unipolar (half-winding) and it would
dissipate
> > 5W
> > > > (1A squared times 5 ohms).
> > > >
> > > > If you connect the windings in parallel, then the winding
> > resistance
> > > > is 2.5 ohms (1/2 what it was in half-winding). You can now
> > increase
> > > > the current to 1.41A and still dissipate 5W (1.41A squared
times
> > 2.5
> > > > ohms = 5W).
> > > >
> > > > What matters here is your torque (from the URL you referenced)
> > > > increased 30%. It should have increased 41%; the reason it
didn't
> > is
> > > > because the iron has magnetically saturated.
> > > >
> > > > If you are full stepping, you don't care. There is no negative
> > > > positioning effect from saturating the iron except for a drop
in
> > > > inductance.
> > > >
> > > > If you are microstepping you do care because saturated iron
means
> > a
> > > > non-linear motor and the microstep positions will begin to
bunch-
> > up
> > > > at the full step locations.
> > > >
> > > > An analogy is an audio amplifier. If you overdrive it with a
sine
> > > > wave, the output will limit or "clip" and produce distortion.
If
> > all
> > > > you are amplifying is a square wave, then who cares if it
clips?
> > > >
> > > > Second point. Take the same motor and drive it at 1.41A half-
> > winding.
> > > > You will not be able to tell it apart from the parallel
connected
> > one
> > > > at 1.41A torque-wise. The only difference is it will
dissipate 10W
> > > > (1.41A squared times 5 ohms).
> > > >
> > > > Third point. This 30% increase in torque occurs at low speeds
> > where
> > > > step motors usually have surplus torque anyway. It does not
get
> > you a
> > > > single extra oz-in of torque at high speed, where improvement
> > would
> > > > be appreciated.
> > > >
> > > > Inductive reactance becomes the bottleneck that limits the
winding
> > > > current. The drive may be set at 1A or 1.41A, it will make no
> > > > difference. 10 mH of inductance will have 62.8 ohms of
inductive
> > > > reactance at 4,000 full steps per second and will limit
winding
> > > > current to 0.5A for a power supply voltage of 31.4VDC.
> > > >
> > > > I = 31.4V / 2 pi times 1kHz times 0.01 Henries
> > > > 4 full steps is one electrical cycle, so 4,000 full steps/sec
=
> > 1kHz
> > > >
> > > > Mariss
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
> > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> >
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> >
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