Re: [CAD_CAM_EDM_DRO] Unipolar/Bipolar Parallel/Series?!?!?

In a message dated 23-Sep-01 14:44:00 Central Daylight Time,
weyland@... writes:

> Am I correct in assuming that I can just run short jumpers inside the motor,
> between screw terminals, to end up with only four wires coming out of the
> motor, instead of having all eight coming out and twisting two wires
> together at the Gecko?
>
> This may sound like a stupid question, but I have to ask it, because their
> are so many seemingly esoteric things I just don't know about electronics
> yet. (like the capcitor in the power terminals if the pwr supply is over
> 12 inches away???)
>

Weyland: There are surely ol' boys with more smarts and experience than I in
this area, but I have, by now, been there, done that, and I am too ignernt to
make up a story too complex for a neophyte to understand, so, I will try to
help:

You kinda "got it". An 8-wire motor can be "strung" to be a four- OR
six-wire (bipolar or unipolar). Remember: If you "parallel" the windings,
so that you have the equiv. of just-TWO windings (four wires), the total
current (that's "amps") draw will be TWICE what it is for each single coil
(or, if you had 'em series-strung as a "six-wire" motor). So, the lead-wires
will have to be appropriate. That is, you don't wanna be using #22 stranded
to conduct ten amperes for 17 feet!

Just be sure, if you really ARE using "screw terminals" that you either use
PROPERLY gas-tight crimps on fine eye-lugs under the screw-heads, or SOLDER
these onto the wire ends, and use bits of shrink-tubing over the "joint" once
cooled (make it look "spiffy", cause that's electrically-better! Yes, it
is!) OR, at least neatly twist 3/4" of stripped-end, TIN those ends, and
"wick" the excess solder off with the iron (tapping the tip on the edge of an
ash-tray, etc., to get the globbery gobs of amalgam/slag off the end of the
iron, each time!). Then, NEATLY bend a "U-loop" in that stripped end, just
so it will snugly hug the screw-threads as you push it on, under the
BINDING-HEAD screw-head, and snug it down. That's nearly as good as a
properly-done wire-lug end. But do NOT try to put TWO such "tinned ends"
under ONE screw, as the "mesh" ain't! It will cut, twist, wrinkle, come
loose, and short the next-nearest, ain't ain't a neat picture!

Capacitor? OK, with steppers and solid-state switchery such as ol' Marliss
has crammed into that tiny Gecko box, when things "change state" (from ON to
OFF, or ZERO to ONE), the "sudden current draw" is kinda like the force the
nail "sees" when the hammer hits its head. If you put more than 12" of wire
between the power-source and the Gecko's terminals, that wire, being a
resistance, though relatively small in numbers of ohms, is kinda like putting
a pinch of sponge-rubber between the hammer and the nail-head. The capacitor
"right AT the Gecko's terminals is kinda like filling that sponge with hard
epoxy, so the hammer's force will have more or less the same effect on the
nail, before the sponge and epoxy do what the WTC buildings did. Only, the
capacitor remains ready to do it again and again, with no dust! BAD analogy,
but, well, I are ignernt! Some might call this a "bypass" capacitor; others,
a "DC Filter-capacitor AT the load". Others, "good sense!". I opt for
all-three, particularly the last!

If your power-supply is not very good — say, poorly filtered (too small a
capacitor of its own), or unregulated, with an "open-circuit voltage" only a
volt or two above what you "want", then there is more reason than ever, 12"
of wire or even less!, for the 470 uF capacitor! (I just hadda go shopping,
and got some TINY 2200 uF caps that'd fit between the + and - input-terminals
of the 210 just fine (oh, but only 25 volt! I'd want more, say, double the
"want" voltage!). 25 is too close to 24, if that's what you would have, even
if regulated, in my opinion.

If you have specific questions like this, feel free to e-mail me direct. I
am "into" steppers, lately, having built four CNC lathes, and PCB drills and
plotters and such, in recent years. I am not a "degreed engineer", but some
say "he be de greedy engine, hear?!"

Jan Rowland, Troll



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