Re: [CAD_CAM_EDM_DRO] Bipolar stepper wiring

In a message dated 11/26/2002 3:33:45 PM Central Standard Time,
erhart01@... writes:

> Can someone explain ... using appropriately small words ... what the
> functional difference is between wiring an 8 wire stepper in series or
> parallel for bipolar operation? I have 3 PowerMax nema 23 motors that are
> 2.8 amp in series and 5.6 amps in parallel. I understand how to wire it,
> but I would like to know what it means to motor operation to be wired one
> way or the other.
>

George: You say you "understand how to wire it"; OK, then you understand
that you are making ONE "longer" winding (more turns) out of two, when you
wire two windings in SERIES. That draws the smaller current, has FOUR times
the inductance. It is the INDUCTANCE that "stores" energy, so the stepping
must be slowed down to permit this "stored energy" to dissipate, for each and
ever step. This smaller current has less "kick", so this takes relatively
longer. Thus, while you might "get away" with a lower-current power-source,
you are SPEED LIMITED.

However, if you wire two windings in PARALLEL, you have the SAME number of
turns, the SAME inductance as one coil, but effectively a "new" effective
winding that can handle TWICE the current. Thus, you can "punch" ;that 5.6
amps into the limited inductance, and REVERSE direction (stepping) faster,
but with the same net POWER (E·I). A better way to do it, if the drive you
have at hand will permit the higher current.

(there are FOUR windings in all for an "8-wire" stepper, and whether series
or parallel connected as described above, there are "two effective" windings,
each with two terminals, i.e. a "4-wire motor")

To reword this explanation: Windings with fewer turns of THICKER wire [in a
stepper motor] can permit faster stepping with lower voltage, but higher
current. Windings with MORE turns (thinner wire) mean you will have lower
current, but higher voltage (to maintain force at low speeds), but the higher
inductance means only slower stepping is possible.

Forgive, as this explanation requires cerebral material in excess of that
I possess, so I have prolly got SOME of it a bit twisted, but HTH
anyway!

Jan Rowland


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