Re: [CAD_CAM_EDM_DRO] servo amps, power supplies; addl endearments

Hi Jack,

Yes, it sounds like you have the power supply built in. If you say
"isolated AC input power", do they want you to run it through an
isolation transformer? But there IS a transformer inside, unless it's a
control transformer. Need to find out! An isolation transformer keeps
you "ISOLATED" from a direct connection to the shop mains. You want to
be isolated. You do not want to have wires or hardware "above ground"
Make sure you are clear on this! ***SAFETY ITEM***. A typical isolation
transformer would have a 115V primary, and a 115V secondary. The two
windings are separate, no connection, and insulated for considerable
breakdown voltage. Think about the old AC/DC radios, with a "HOT"
chassis. Take the chassis out of the plastic case, And you can get
KILLED if you touch the chassis (depending on which way the plug was in
the wall outlet, bad filter or bypass cap etc.). ***SAFETY ITEM***

More below:

jmw@... wrote:

>
> Alan, Jon et al thanks for your thoughful replies to my previous post
> re servo amps and power supplies.
>
> After reading the docs for the Baldor UM4-100 amps-in-a-cage I've
> got, I'm starting to think that the power supply for the axes motors
> is built-in. i) The chassis has a transformer and cap each of which
> are half-beer can sized (12 oz, not a Foster's), ii) the specs call
> out "rated bus input nominal 70-105 VAC" and "nominal output voltage
> 100 VDC", iii) the chassis connections diagram shows "isolated AC
> input power 70/105 VAC," "logic and fan power 115 VAC," and black (-)
> and red (+) wires heading out to the motors, and iv) the catalog
> says, "The chassis includes the power supply, over voltage protector,
> and associated hardware," and finally v) poring over the docs for the
> terminal block doesn't reveal anything like "100 VDC in." I guess one
> way to find out will be to connect the thing to a motor and see if
> spins. Before doing that, however, I'd like to find out what an
> isolation transformer is.
>
> The "typical connections" diagram for the individual amp cards shows
> a tachometer with two leads going to + and - tach terminals, plus
> limit switches and interlock/reset, and something called "motion
> controller +/- 10 VDC signal" with leads going to "differential"
> and "signal input" terminals. So, what is "motion controller"? This
> sounds suspiciously like the brains of the operation, so I assume
> it's the soon to be released servo card Jon is working on.
>

the tachs are speed feedback from the motors, and the limit switches
shut things down if the axis travels too far. Interlocks are switches
that kill the voltages/movement if the wrong "door" is opened.
***SAFETY STUFF***.

The +/- 10v signal sounds like the "error" signal that drives the motor
amps. It has to be generated by servo controller electronics (motion
controller ?), the circuitry that compares the commanded position with
the actual position (encoders). You might need another Baldor board! I
don't know if Jon's board will do all of that! The servo system needs
something like a PID controller to do that stuff. Big Job. I think
Jon's board was doing rate generators? Jon?

> Where do the rotary encoders fit into this scheme? Do the encoder
> outputs run to the PC-servo card and that card sends output to the
> motion controller terminals on each amp card? Or are the encoders
> themselves the so-called motion controllers and there's another type
> of connection between the PC-servo card and the amps?

Ouch, not sure of your questions. Encoders are usually just simple
"optical switches". They send pulses (digital) or sine waves (analog) to
the motion controller. Try to find a big block diagram for the
equipment that you have sub-assemblies for.

>
> What is the relationship between the nameplate voltage on the amp and
> that on the servo motors. If "bus voltage" is 100 VDC does that mean
> I'm hunting for 100 VDC servos. I do understand that the continuous
> wattage rating of the motors should not exceed that of the
> amplifier. Whether the amplifier's ratings (100 VDC 6/15 AMPS
> cont/peak) is for _each_ motor or all three (or four) only the
> technical writers at Baldor know for sure.

Probably. There again, best to see what Baldor had in mind! Find the
required Baldor motor, and find a replacement's spec's.

Hope this has helped a bit. Again, please be CAREFUL with the "SAFETY
ITEMS"! We want to keep you around.

Alan

>
> Lastly, I've checked through the archives, but can someone suggest a
> source for Bport-sized PMDC servos w/ tach? Maybe some high stepper
> has a redundant pair for sale?
>
> As always, thanks very much for the carefull considerations my
> questions have gotten on this group.
>
> --Jack W.