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

Jeff -

An interesting problem - without knowledge of the motor's current rating,
it is a little difficult to advise on a current setting for the controller
cards.

From your earlier posts, it sounds like the original drives may well have
been simple L/R drives (using power resistors in series with the motor
coils to limit the current). If this is so, then you should be able to work
back to the motor current rating; divide the supply voltage by the ratio of
the motor coil resistance to the series power resistor value to get the
voltage needed to drive the max current. From I=R/E you can then work out
what current that voltage will drive through the motor coil
resistance. However, to do this successfully, you would need to know what
the drive circuitry really is - whether it is a "simple" L/R drive, or a
more sophisticated drive (a bi-level chopper, for example). If the latter,
then it may not be so easy to determine by this method.

An alternative "empirical" method might be to hook one motor up to a drive,
and adjust the current up until the motor gets warm (giving enough time
between current increments for the motor temperature to stabilize).
Steppers are generally designed to run warm; if you set the current such
that the motor gets warm (but not too hot to touch) you probably are not
far off the right current setting.

Regards,
Tony

At 11:04 13/02/2003 -0500, you wrote:

>Guys:
>
>I really appreciate the input. I'm a newbie at this and your discussion is
>very helpful. As a follow on question:
>
>I have the following challenges:
>The DC power supply of the NC controller I'm cannibalizing puts out 130V. I
>don't know if this eventually reached the motors or was reduced somewhere
>else in the old NC drive section before reaching the drives. (There was a
>short circuit somewhere in the unit, so I disconnected all the controls,
>drives etc so I could work on the power supply). I can rewire the taps on
>the transformer to give me either 62 or 68 volts DC, both of which fall
>below the range of the 80v max of the CMD260 drives I bought.
>
>Based on the input you guys gave (my NEMA 42 steppers are unmarked and
>undocumented) I'm going to try running them in parallel. I really don't
>want to generate sparks and a puff of smoke. What would you recommend the
>current setting on the drives to be placed at (they go as high as 8 amps)?
>Should I drive them with 62 volts or 68 volts?
>
>Thanks in advance,
>
>Jeff
>
>
>-----Original Message-----
>From: turbulatordude <davemucha@...> [mailto:davemucha@...]
>Sent: Thursday, February 13, 2003 8:33 AM
>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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Regards,
Tony