Re: Allen Bradley Servo Drivers

David L Anderson wrote:

> From: David L Anderson <daveland@...>
>
> Hey servo guys
>
> I have a set of 3 allen bradley 1388 DC PWM servo drivers and the
> transformer (3 phase). I also have one baldor servo motor with tach and
> encoder in unknown condition. I have several questions if someone is
> familiar with this setup.
>
> 1) Can I use a rotary single phase to 3 phase converter to run the
> transformer for these drivers? How about the "static " converters. I don't
> have 3 phase power. ( note that the drives are .75Kw continous and 3.75KW
> peak for each axis)

Depending on how the transformer windongs are set up, it may make more
sense to just get a suitable single-phase transformer with the right output
voltage and hook it up to the servo amps. the 'static converters' are really
just starting caps, and would definitely not work.

> 2) The drivers can drive 700 watt servo motors (150V 10 amps Cont 25 A
> peak). I have no data on the baldor motor since the name plate is
> illegible. any other way to identify it?
>
> 3) the motor feels a bit "grindy" can I open up the encoder end without
> destroying anything?

Do this with great care. The encoder may be integral, with the disc attached
directly to the end of the motor shaft, or it may be adapted to the motor with
a flex coupling, and have its own bearings.

> Possibly a worn bearing? How about connection
> diagrams? Can this motor be sent out and rebuilt?

Sure, but you'll have a heart attack when you find out what a bunch of
thieves the CNC machine tool service people are. They charge what they
can get away with, not what they are worth. Like the guy who was quoted
$1500 plus 4 hours minimum work time at $150/hr., plus 2 hours commute
at $65/hr. to replace a gel-cell memory backup battery on an Allen-Bradley
CNC control. He did it himself for about $35.

> 4) Would this be a good setup for EMC if I bought the servo-to-go board and
> used it to drive the 1388 drivers? I would still need to buy two more servo
> motors with encoders ($1000 a piece for new Baldors with 1000 line
> encodes).

Assuming the servo amps are designed for +/- 10 Volt input, they should
work fine with the STG card.

> I would like to get the existing motor operational and use it to prove that
> all three drivers are functional. Any help would be appreciated.

Do these servo amps need a tach input? Do they derive velocity from the
encoder signals? It sounds like they run a DC bus of about 170 Volts, DC.
A step-down transformer set up to produce 120 V AC output, and then
run through a bridge rectifier and a filter cap would do that. These parts
are probably on the servo amp, but using a single-phase input, the filter
cap might need to be increased.

Jon