Re: Power Supply Calculations

If your worldservo amps are the ones Dan Mauch has on his site,
the manual says they are looking for a 75V nominal supply (84V
shutdown). At that voltage, just about any powersupply design for a
geckodrive servo amp should work just fine. Your motors should have
plenty of torque, but your top speed will likely be reduced
considerably.

As far as an actual power supply design is concerned, you should
take a look at:
http://www.a-m-c.com/download/power_supply_selection.pdf

Generally, you will want a step down transformer that will get you
less than 53VAC, which will be run through a bridge rectifier,
getting you less than 75 VDC, but with a bunch of ripple. You will
need a fair chunk of capacitance to smooth this out, depending of
current draw. (I know there was a rule of thumb floating around about
this, check the archives). Total current capacity is a bit of a toss-
up. It really depends of how hard you are driving the motors, and in
how many axes. You would probably be fine with a supply that could
supply maximum current for just one drive. (The only time an amp
will draw full current is when you are trying for full torque at full
speed, which probably isn't very often.) One of the benefits of PWM
amplifiers is that Power In ~= Power Out (yes, you lose some from
inefficiencies, but it's not whole lot.) So you could very easily
get 20 amps at a low voltage (speed) from each amplifier, all from a
common 20 amp 75V supply.

Hope this helps.

- Cameron Murphy


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "natchamp_87" <mark@h...>
wrote:

> Is there a secret hand shake I'm not aware of? <just kidding>. I
> was thinking about this and wondering if I'd be better off using 3
> seperate power supplies rathar than one large one. Can anyone

please

> help?
> Mark
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "natchamp_87" <mark@h...>
> wrote:
> > Ok guys, I'm switching gears on my project and need some help.
> > Previously, I was going to use some AC drives for my brushless
> > motors so I didn't need a separate power supply. Now I do
> > because I recently purchased some WorldServo drives (so I can use
> > step/dir software) and need to figure out what power supply to
> use.
> > I'm having problems figuring it out. My project is retrofitting
> > a Bridgeport M-head. My motors are probably a little overkill so

I

> > know I don't need to max them out.
> >
> > Using the formula of Amps = 2/3rd of the motors rated amps I come
> up
> > with the following
> >
> > Motor RMS is 7.5, so 7.5*.6666 = 5amps However, do I triple this
> > (for all 3 motors) to obtain the whole power supply rated amps
> > requirements?
> >
> > The voltage part of the equation is hard for me because I don't
> > know what motor spec to use to multiple by 3.
> >
> > Here are some of the specs for my motors:
> > Stall torque 780oz
> > Peak torque 2,000 oz
> > Rated power 1,400 watts
> > Const stall current 10.6A peak
> > Const stall current 7.5A rms
> > BEMF constant 62 volts peak/krpm
> > Resistance 25c 1.2 ohms
> > Inductance 3.8 mH
> > Recommend bus Voltage 320 VDC
> >
> > Can anyone shed some light on determining what power supply I
> need?
> > Thanks a bunch.
> >
> > Mark