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

Thanks for all the help. One last group of questions based on a couple of
suggestions from Tim Goldstein. I've tried to lay the variables out clearly
so it's a little long:

To bring you up to speed:
I have tentatively identifies my 8 connection unmarked NEMA 42 stepper
motors which are directly connected to my Bridgeport Milling machines X,Y
and Z axis as the following:

2.1 volts, 9 amps (based on a photo of a nameplate of a similar motor and my
winding resistance being within 25% - .29 ohm measured to .23 ohm calculated
based on nameplate in photo values)

max voltage at 25 times rated voltage would be 52.5 volts DC

I have two power supplies from the original NC controller, each with a
transformer about half the size of a shoebox (an informal, but descriptive
specification for both of them) and capacitors the size of beer cans.

Each transformer has 105, 115 and 125 volt taps on the primary (currently at
115v)

Each transformer has a double wound secondary

The first transformer has its two 12 volt secondaries wired through
individual rectifiers and capacitors and then in parallel on the D.C. side
for an output of 16.7 volts DC

The second has two 44 volt secondary windings (with 22 volt center taps)
wired in series for a final power supply output of 130 volts DC

Now to the questions:

1)
Which of the following power supply setups makes most sense (the apparent
best voltage has both secondary windings in series - how does this affect
its ability to handle three NEMA 42 steppers):

Using the 125 volt primary and 44 volt secondary would give:
115/125 * 44 * 1.414 = 57 volts (10% too high based on 25 times rated volts)


Using a 105 volt primary tap and a 22 volt secondary tap on the same
transformer would give:
115/105 * 22 * 1.414 = 34 volts

OR

Using the 105 volt primary tap on the other transformer with the two 12 volt
secondary windings in parallel:
115/105 * (12+12) * 1.414 = 37 volts

2)
Tim Goldstein suggested that I wire my 8 connection stepper at half coil. I
have a diagram showing parallel and series connections (and a 6 terminal
motor diagram of a half coil connection). Any suggestions where I can find
a half coil connection description for an 8 terminal motor? What do I lose
if I wire it this way (is there a free lunch?)

3)
Since I'm changing the voltage in the power supply from either 16.5 volts or
130 volts (depending which supply I use to about 35 volts, can I continue to
use the same capacitors? (and same size bridging resistors)?

Thanks much for all of the assistance.

Jeff

-----Original Message-----
From: Tim Goldstein [mailto:timg@...]
Sent: Saturday, February 15, 2003 3:32 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: RE: [CAD_CAM_EDM_DRO] Re: QUESTION ABOUT SERIES OR PARALLEL ON
STEPPER MOTORS - ref post 52721


At 25X over voltage it will run quite hot. At more voltage it will run even
hotter. The 25X value is empirically derived as the general upper limit
based upon the motor heating. It is not a absolute limit, but you have to
consider the potential you will damage the motor by over heating it.
Personally I find that even at 25X the motors run hotter than I like. Not
that it is beyond the spec, but I don't like having the motors at a
temperature that will cook meat. If it was my machine I would likely set it
up with 36 - 48 v and wire it as half coil. Series will seriously limit your
max RPM and parallel takes a lot of amps. Half coil cuts the amps while
giving almost all the speed of parallel.

Tim
[Denver, CO]
Sherline products at Deep Discount
Mach1 & DeskCNC with credit card ordering www.KTMarketing.com/Sherline Now
selling Visual Mill

> -----Original Message-----

> The nameplate on his motor rates it at 2.1 volts and 9.2 amperes.
>
> Is it OK to drive this at 62 volts DC? I read that the
> voltage should not exceed 25 times the rated voltage which
> would be 52.5 volts.
>
> Since the application is a direct connection to the XY and Z
> axis of a Bridgeport Milling machine, (and since the drive
> tops out at 8 amperes) is it better to try running it at 8
> amperes in parallel or at 4.5 amperes in series?
>
> Again, thanks much for all your help.
>
> Jeff