Re: [CAD_CAM_EDM_DRO] Blown g201 is it the motor?

barker806 wrote:

>Hello There seems to be a problem with the set up that I have on a
>machine. There is 208 3 ph (Delta) going to a transformer. The
>transformer is single phase with two legs of the 208 on the primary
>side of the trans. coming off from secondary side I am getting 53 VAC
>which I have both legs fused. after the fuse there are three full
>wave rectifiers. From the rectifiers all the positives are conected
>to all the positives and all the negitives are hooked to all the
>negitives, ground and the ground of the drive. the power from the
>caps goes through a fuse to than a drive with a voltage of 76 volts.
>
>I have this same setup on an other machine and it works well...
>
>Here is what happend
>I hooked up the Z moved it up and down worked very well
>then power down
>Hooked up the X moved very welll
>then power down
>Hooked up the Y turn on the power and there goes a drive and it blew
>a fuse The drive died and the 10amp fuse blew going to the
>rectifiers. the 3amp fuse at the drive did not blow (May be a slow
>blow) .
>The x and z drives are still working very well when I took the Y
>drive out.
>
>The drive reads a dead short from the Power ground pin to the 24 -
>80v pin as well one of the motor coil pins The enable / disable pin
>from the y drive if hooked up (No power) will disable the other
>drives. (It didn't do that before)
>
>What I need to know is what will cause that failure to happen. I
>DON'T want to hook up an other drive (I have others on other
>machines) because it blew on power up. So what will make this happen
>I have checked and there is no coil to ground fault that I can read.
>the motors are Bridgeport series 2 steppers and with 40V I can get 30
>in per min and at 74 I get 70 in per min (I like the higher voltage).
>
>

First, take an ohmmeter and check every wire to the motor for continuity
to ground. Most likely with this spectacular a failure, it has a grounded
connection somewhere, either the motor or the wiring. The Geckos do not
have any way of detecting a grounded motor, and the fusible element becomes
the high-side transistors. But, you say you have already checked this.

If this doesn't show any problem, check the wiring against one of the
working
motors. You should read a low reading (a couple of Ohms) between the two
wires of each phase. There should be no continuity between one phase and
the other. (It is easy to get the two phases mixed up, and this is
supposed to
be bad for the Gecko.)

If you STILL have not found a problem, then try comparing the winding
resistance between this motor and one of the known good ones. It will be
hard to get an accurate reading on such a low resistance with a plain
DVM, though. But, a significantly lower reading is an indication of
a possible burned-out winding. You might make the readings directly at
the motor to exclude the resistance of the cable. If you find something
that
looks significant, you can try a D cell across each phase. You should get
a sharp click from the motor when yo do this. You can then apply force
to the motor and gauge the holding torque.

Note that a single shorted turn dramatically reduces the inductance of a
motor winding, and can cause the Gecko drive to go up in smoke. It won't
significantly affect resistance ratings or holding torque with the D cell!
But, it might make a decidedly weak "clunk" instead of a sharp click.
These kinds of defects can be very hard to diagnose.

Jon