Re: [CAD_CAM_EDM_DRO] big lathe, big motors may have both armature and field windings

Doug Fortune wrote:

> Big Iron Veterans and Motor experts:
>
> I have a 1980's vintage Jones & Lamson lathe
> (12,000 lb class, 20/30 HP spindle, 3.5" spindle bore,
> 18" swing), in other words, "Heavy Metal". Actually,
> I've got two of them, and this is the smaller one.
>
> The current Allen Bradley controls may or may not
> be ok, but that doesn't matter because it is being
> retrofitted to PC control (besides, someone lost the
> 8" boot floppy!). I know that software for constant
> surface speed cutting and threading isn't quite there
> yet, but I'm sure we'll have it sooner or later.
>
> The main spindle drive ("Reliance Electric SuperRPM DC Motor")
> is labeled 3 phase 240V 72A, and also field winding
> "STR SHUNT" 240V 3.18A, hot amps 2.50/.40
> and there are four wires going into it: two thick cables,
> and two (say 14 GA) wires.
>
> I therefore assume the motor is a 2 wire armature,
> 2 wire field universal AD/DC reversable motor.

I severely doubt that a 20/30 Hp motor is a universal.
The nameplate describes it as a DC motor, anyway!
A universal motor requires that the field flux reverses
60 times a second with the armature flux. Due to the
large inductance of the field winding, that is just impossible.

>
> ( What does the "hot amps 2.50/.40 " mean?).

Hot means that the measurement is taken after the winding
has warmed up to operating temperature. This often makes
up to 10% decrease in field current, as the resistance of copper
rises fairly rapidly with temperature.

The two numbers are current for the low range/high range
motor speeds. You run 2.5 Field amps for low speed, and .4 A
for high speed. The 3.18A must be the worst-case cold
field current draw. The 3 phase 240 V 72A must be the
input to the rectifier for the armature. it may use an SCR
rectifier setup.

>
> There is a Reliance V*S SpindleDrive variable spindle
> speed control unit about 14"square x 4" thick that
> seems to convert the 480V AC into 240V DC, and it looks
> Ok. I think I might be able to use it as-is if I can
> figure out where the input speed control is (probably
> a +/- 10 volt analog signal?) and maybe control that
> manually with a pot, or through the PC with a D/A card.

Yes, it is fairly likely to take something like +/- 10 V.

>
> Q#1
> If anyone wants to give me an opinion on any aspect of
> the above main spindle motor, please do.
>
> -----------------------------
> The two servo motors are a mystery: Kollmorgan Corp
> Inland Motor Division Model TTR-4030-102-A
> continuous 15V 20 Amps 10 lb*ft torque ie 1920oz*in
> peak 67V 90 Amps 45 lb*ft torque ie 8640oz*in
> max rpm 2000
>
> Like the spindle motor, they have four wires too,
> two thick, two thin, and I am presuming the two thin
> wires are also for the field winding (control circuit).
> But maybe they are merely for a brake, I don't know.

I first thought these were for a tach, but your next sentence
indicates they are not. Most Kollmorgen motors are
permanent magnet, but it is possible that they are not.
You might see what they are connected to at the servo amp.

> Atop the motors is a DC tachometer (18.9V/1000 rpm)
> that seems to be separate from these other four wires.
>
> Q#2
> Does anyone have an opinion on these? If there were
> only 2 wires, I'd be tempted to hook up gecko's
> (80 V and 20 A) and let her rip. If the motors fry,
> I'd have them rewound for 80V and 20A and try it again.

I doubt you can get the motors rewound. A number of
Kollmorgen motors have printed windings made out of
printed circuit boards. Many servo motors can't even
be disassembled without special keepers to prevent
demagnetization of the magnets. I suspect the Gecko
drives may be too small for these machines. You might
try to get info on the existing servo amps to see what
their peak rating is. It may be that they never delivered
the full peak rating to the motors. But, I'll bet they delivered
more than the 20 Amp continuous rating of the motors.

>
> I guess I have to take one of the motors out and take
> it to a specialist to see what they are (Inland doesn't
> answer my email inquiries). But if someone here has a
> good idea of what the two extra wires are (or has some
> old documentation or specs), so much the better.

I doubt you will find such a 'specialist'. Most motor repair
places won't even look at a DC motor of any type, and start
backing away slowly with a stricken look when you mention
servos. You might take an ohmmeter reading of the terminals
with the thin wires. Oh, yes, do they have odd colors, like
red and yellow? They may be thermocouple wires, to detect
motor overheating. This was fairly common on older CNC
systems. They may not even be connected!

Anyway, if they are permanent magnet DC (ratings sound VERY
detailed, yet no mention of field winding) you are not likely to
hurt them with a Gecko drive. But, you may not get the required
performance from them.

Why not use the servo amps already in the control?

Also, you don't make any mention of the encoders/resolvers
or linear scales used to sense position.

Jon