RE: [CAD_CAM_EDM_DRO] Re: QUESTION ABOUT SERIES OR PARALLEL ON STEPPER MOTORS - ref post 52721

As far as I understand it....

a stepper motor coil can be thought of as a perfect resistor in series with
a perfect inductor.

considering a static (holding) state

The magnetic field in an inductor (and hence stepper torque as the coils are
inductors) is proportional to amps X turns

Whether the coils are in series or parallel, there are still the same number
of turns on each coil, and the wire of each coil is still the same
thickness, and can therefore take the same maximum current in each coil, so
series or parallel there is still the same STATIC field strength available,
its just that in SERIES the voltage required to push the maximum current
through the stepper coil's resistance is twice that of a PARALLEL connected
pair.
and in PARALLEL, the current is twice that of a SERIES connected pair.
(Voltage X current = power, and that stays the same in each case)



However in a dynamic (i.e. moving) state, it's a totally different kettle of
fish...



With a constant voltage across an inductance, the current will increase at a
constant rate against time.

The inductance of the parallel connected pair will be 1/4 that of the series
connected pair

Quarter the inductance and the current will increase at four times the rate.

This means that the current in the parallel connencted stepper coil pair
will increase to a level where it is limited either by the control
circuitry, or the internal resistance of the motor 4 times faster than the
series pair. As I said at the top, stepper torque is proportional to
current, so limit on torque will be reached at a much higher speed,
(theoretically 4X faster) for a parallel connected pair than series.

Whilst on this subject, this is the reason why current controlled drivers
are used with supplies at a much higher voltage than the steppers are DC
rated at. The high voltage is there to force the current in the coil
(inductor) to rise more quickly, up to it's limit, but in this case it's
limit is controlled by the current controlling driver, rather than the
stepper motor coil's DC resistance.

Has that confused anyone further?
Nig



-----Original Message-----
From: turbulatordude <davemucha@...> [mailto:davemucha@...]
Sent: Thursday, February 13, 2003 1:33 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: QUESTION ABOUT SERIES OR PARALLEL ON
STEPPER MOTORS - ref post 52721



The serial vs. parallel speed question was tossed around by the pros
from Dover a little while back.

This is real close of an explanation. if you want more, read the
whole thread.


Message 52721 "jeffalanp" <xylotex@h. . . > Date: Tue Nov 19, 2002
12:56 am Subject: Re: Running Unipolar steppers with a Bi-polar
driver?

"Mariss, OK, OK, I got it (I think). The inductive time constant for
both parallel and series motors will be the same (t=L/R, the time it
take to get to 62. 3%). But to overcome the increased inductance and
resistance in a series wound motor (compared to parallel), I would
need to double the voltage to achieve the same time as parallel. "

There was more on the post, time to charge the coil, discharge it,
then reverse direction, that sort of stuff. but this is enough data
for most of us to understand the differences.

Or the short and sweet, series goes thru a longer wire and that takes
more time. You can did deeper and get more data.

Dave





--- In CAD_CAM_EDM_DRO@yahoogroups.com, Alper YILDIRIM
<yildirimalper@y...> wrote:

> Hi,
> Take a look to the following site:
>
> http://www.microkinetics.com/contab.html
>
> For the bipolar series and parallel connections the
> time constant L/R is same. For parallel connection,
> inductance lower 4 times but resistance lowers 4 times
> too. So the time sonstant does not change.
> Can someone explain why parallel wiring allows higher
> speeds according to this approach.
>
> Best regards
> Alper
>
> Jon wrote:
>
> ""Yes. In almost all cases, the parallel connection
> is better. It
> provides lower inductance,
> and therefore, higher speeds, than the series
> connection. The only
> time
> to use series
> is if your stepper driver cannot supply the current
> needed for parallel
> connection, and
> if high speed is not important. (The fix is to get a
> driver that CAN
> handle full rated
> current in the parallel mode.)
> Jon""
>
>
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