Re: [CAD_CAM_EDM_DRO] servo amps and power supplies; terms of endearment

jmw@... wrote:

> I've got a servo amp with 4 boards, each rated to run a (permanent
> magnet DC servo) motor 70-100 VDC at 15 cont / 25 peak amps. The unit
> has an integrated power supply for its own requirements--but zilch
> for the motors.
>
> What I'm wondering is how the amp communicates with the power supply
> so as to vary the power supplied to the motors?

The amp takes constant voltage DC from the power supply, and modulates
it (by rapidly turning its transistors on and off) to produce a lower average
voltage to the motors. So, the amp doesn't have to tell the power supply
anything.

> Does the amp just
> tell the individual motors to run faster or slower and so each just
> pulls more or less from the well? Maybe the amp sends voltage and
> amperage codes to the power supply and it adjusts its output (but
> this would require a power chanell for each motor, right?) Maybe the
> full output of the power supply runs through the amp and four demons,
> one for each motor, regulate the flow to each motor.

Actually, there would be four 'demons' for each motor. These can be
thought of as 4 knife switches that can connect each motor terminal
to either the + or - terminal of the power supply. These switches
are actually transistors, controlled by some logic in the amp.

> As I've stated before, I'm not an EE. I figure I could probably
> figure out how to make a simple DC power supply, but depending on the
> complexity of the controll scheme I might just try and find one
> surplus.

A very plain, unregulated, DC power supply is all that is needed.
There is NO 'control scheme', that is all taken care of INSIDE the
servo amp.

Jon