Re: servo voltage question

Mike, are you talking about this motor...And what pulley ratio are
you running and what rapids do you have...

900 RPM AMETEK, #965922-101. Permanent magnet DC motor rated 38 VDC
nominal. Reversible, ball bearing. Max. rated rpm is 1300 max.
Armature current before permanent demagnetization is 12 amps. Torque
constant is 50 oz-in per amp. Terminal resistance 20 ohms +-20%.
Voltage constant is 37 VDC per 1000 rpm. When tested on 38 VDC, we
recorded the following data: No-load spedd 1100 rpm @ 0.260 amp. With
a 100 oz-in load the shaft speed was 900 rpm @ 2.3 amps. When tested
as a generator at 1000 rpm, the output was 5.8 amps @ 12 VDC. Shaft:
5/8" dia. X 1-5/16" long. The opposite end of the shaft has a turned
down diameter and a flat mounting area with two sets of tapped holes.
This was probably originally intended for an encoder or tachometer
mounting. This shaft has an outside dia. of 3/16" and is approx. 3/8"
long. We do not have the encoders whtat were mounted on this motor,
but suitable encoders are probably available from encoder suppliers
if required. The motor has five #10x32 tpi tapped mounting holes on
the shaft end of the motor body. Electrical connections are via 3-
1/2" long flexible wires. Dimensions: 4" dia. X 4-1/2" long
(excluding shafts). Stock #DCM9951 $44.95



Wally






--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mike Phillips"
<mikep_95133@y...> wrote:

>
> I run the 38vdc Ameteks in my BP retrofit at 75vdc for 3 years now.

It

> quadruples the horsepower which translates to more accuracy through
> better holding power. Rarely do they even get warm.
>
> Mike
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...>

wrote:

> > cnc_4_me wrote:
> >
> > >What power supply voltage do you use for servos with a pwm
> > >drive...Example, if your motor is rated for 40VDC do you use a

40VDC

> > >power supply or do you use something higher like 70VDC...
> > >
> > >
> > I've been having a minor war with Mariss Freimanis at Gecko over

this.

> > You have to know how the voltage rating of the motor was written.
> > If it is an absolute voltage limit, never to be exceeded, then

you don't

> > want to go over it. This will be true for "real" servo motors

made by

> > such makers as Electro-Craft (now Reliance Electric), Yaskawa,

Fanuc,

> > etc. Those motors also have a peak current rating, which is also
> never to
> > be exceeded.
> >
> > But many motors sold in the servo market have a very different

voltage

> > rating.
> > Makers such as Ametek use this. It is a "bus voltage" rating.

You can

> > connect
> > the motor to a DC bus of that voltage with the motor stationary,

and

> it will
> > not be harmed. To illustrate, the typical Ametek motor, sold by
> > Camtronics and
> > many others, has about a 4 Ohm armature resistance, a 12 A peak

current

> > rating, and a stated 40 V maximum voltage. Simple Ohm's law

calculation

> > states you can NEVER even obtain 12 A through this motor with a

40 V

> > power supply. I = E/R or 40/4 = 10 A! Now, with the motor

running at

> > 1/2 its rated speed, the back EMF will be about 20 V. That

subtracts

> > from the
> > applied voltage, so you'd only have about 20 V left to drive

current

> > through the motor.
> > With a 40 V power source, you can only get (40-20)/4 = 5 Amps!

If you

> > want to
> > spin the motor faster, there's even less current possible. So,

by

> > limiting the supply
> > to the 40 V rating, you lose at least HALF the possible power

output of

> > this motor.
> > But, you can't "erase" the magnets in it with only 40 V. If you

turn

> > the voltage up
> > a bit, the only thing standing between the the motor and

destruction of

> > the magnets
> > is the servo amp's current limit. If you trust that current limit
> to do
> > its job, then
> > you should be able to safely turn up the supply voltage to get

rated

> > performance
> > from the motor.
> >
> > Now, that gets you into the safe operating area discussion. The

motor

> > CAN be
> > made to safely deliver maximum rated speed and maximum rated

torque

> > simultaneously
> > for only some time interval. If you need both at the same time,

you'd

> > better not
> > demand it for more than a fraction of a second a couple of times a
> minute.
> > Really massive industrial servos are designed to survive more

severe

> > service than
> > lighter commercial-grade motors, and those often don't come with

safe

> > operating
> > area curves. So, you have to use some common sense in how far

you are

> > going to
> > push things. And, of course, a Gecko drive will happily deliver

10

> A to
> > a locked
> > Ametek motor until the smoke comes out. I've seen it happen!
> >
> > Anyway, Mariss warns to strictly adhere to the manufacturer's

ratings.

> > But, I hope
> > I have shown that at least with some motors, you absolutely

cannot even

> > achieve rated
> > performance if you do that.
> >
> > Jon