How do you test a DC servo motor

On Jun 5, 3:53=A0pm, Ignoramus23517 <ignoramus23...@NOSPAM.
23517.invalid> wrote:

I don't know about 4 big pins.  Should just be +/- pins for power.

The set of small pins would be the encoder (or resolver) for feedback.

In any case, apply power to the main power pins and it should spin.  A
good first test would be to ohm out the windings.  "Normal" will be
3-4 ohms.  If you have a set, it will give you a population study for
normal.

Do you have an asking price in mind?

JW

A DC servo is just a DC motor with a feedback device. Resolver and tach for
old ones, encoder for new ones. Check motor operation by hooking large wires
to a 12 volt battery.

Many fanuc servos are AC brushless units, quite a different animal. I don't
know of a way to test them without connecting to a servo drive.

karl

Thanks, guys, I posted a followup in a separate thread about actual
testing.

i

On Fri, 05 Jun 2009 15:53:22 -0500, Ignoramus23517


They're almost certainly brushless motors, which are essentially
3-phase permanent magnet synchronous motors. The "many small pins" are
the connections for the commutation feedback, which is most often 3
Hall effect sensors that tells the drive the angular position of the
rotor. If there are more than 10 pins or so, there may be encoder
connections mixed in there as well.

You can drive a brushless motor with a VFD (without the commutation
feedback), but getting the VFD's parameters set properly is not
trivial.

If the resistance of the motor's 3 phases is equal, and it generates
an equal voltage on all 3 phases when you spin it, the motor itself is
probably OK. I'm not sure what you could with limited equipment to
test for other potential problems like a failure in the Hall sensors,
insulation breakdown, or a demagnetized condition.

--
Ned Simmons

Ned Simmons wrote:

Old Fanuc DC servos have yellow end caps and have brush ports with screw
caps, newer Fanuc AC servos have red end caps and no brush caps. If I
recall, the DC also have round bodies and the AC have square bodies. In
either case the big connector with small pins is for the encoder and the
smaller connector is for the servo.

One prong is for motor ground, another one has no connection at all

The other two go to the brushes, connect a car battery to them see if it
spins

The other connector goes to the encoder, suggest dont mess with those.

--

Ignoramus23517 wrote:

1) Find nameplate.
2) Identify model and/or part number(s)
3) Google "Fanuc" plus numbers from step 2.
4) Proceed with testing based on motor specs located in step 3.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Experience is the worst teacher.  It always gives the test
first and the instruction afterward.

short out all the big pins together and try to turn the shaft.  There should
be a high resistance to rotation.
Remove the short and the motor shaft should turn easily.  This is a quick
test but does not necessarily test every parameter of the motor.  The
encoder and tach generator will not be tested.

I would be interested in purchasing the motors if you are going to sell
them.

John