RE: [CAD_CAM_EDM_DRO] Re: Servo motor voltage

Yes, I picked up the R value wrong from your specs... I will use the 1 ohm value since it is higher.
Ldi/dt+Ri+Ke*kRPM=(small if controlled)+1*8.9+25*2.100=61.4V
So in this case the 66V power supply should be sufficient if it can source 8.9A continuously.

If the speed is 0 and the max current is used, then the voltage is
1*44.5=44V (momentarily)
so again the 66V should be fine... but I would verify the 1 ohm is still valid at 44.5A. Also verify the power supply can handle the peak currents.

Some other advice, make sure there is sufficient capactiance and a diode to prevent regenerative current from the motor during braking from wrecking the power supply. I recently purchased a powersupply designed for servo amps that you may be interested in. It is from Copleycontrols. http://www.copleycontrols.com/motion/amplifiers/accessories/
The 65V, 15Amp continuous powersupply fits the bill. It can handle 2.5xcontinuous current rating in peak cases, so it should suit your application. (I ordered mine from www.clickautomation.com) I haven't received it yet, but expect it to be good based on other friends' experiences.

Darcy

-----Original Message-----
From: bru103 [mailto:bru102@...]
Sent: Tuesday, April 01, 2003 8:40 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Servo motor voltage


I'm a new guy just following along....but I wonder if Darcy might
have picked up the wrong value for "R" in the formula. If I
understand the calculations, 4 ohms is being used, and that isn't
the spec...it was .75 to 1.02 ohms at 4 AMPS, not 4 OHMS. If I got
it right, that makes a big difference in the required voltage.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Parker, Darcy "
<dparker@p...> wrote:

> I think you may need more than 66V.
> Ldi/dt+Ri+Ke*kRPM=(small if controlled)+4*8.9+25*2.100=88.1V
> (Ldi/dt) should be small if controlled because i is proportionate

to Torque and you can control

> the rate of change of torque. Also L tends to be small...
>
> If the speed is 0 and the max current is used, then the voltage is

4*44.5=178V (momentarily)

>
> Your estimates may be too high, or you may want a higher voltage

power supply (and servo amp with higher rating)or a combination of
the two.

>
>
> -----Original Message-----
> From: Chris Baugher [mailto:cbaugher_yahoo@b...]
> Sent: Tuesday, April 01, 2003 1:26 AM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] Re: Servo motor voltage
>
>
>
> Hmm, I guess I'm not sure where you got the 48V from. 48V was for

the

> transformers I'm looking at. Anyway, here are the motor specs I

have:

>
> 3 Electro-Craft DC Brushed Servo Motors, Model E712
>
> 37.51 Oz-In/A
> 25.0-30.5 V/KRpm
> Motor Terminal Resistance .75-1.02 Ohms @ 4A.
> Maximum Terminal Voltage 60V
> Maximum Continuous Speed 2100 RPM (No Load)
> Maximum Peak Torque 1500 Oz-In.
> Maximum Peak Current 44.5A (I think - the scan I have is very

blurry)

> Maximum Continuous Stall Torque At Max Motor Temp 300 Oz-In.
> Maximum Continuous Current 8.9A
>
> So what I want to know is if a 66V supply will be ok for these

motors.

>
> C|
>
>
> On Tue, 1 Apr 2003, Mariss Freimanis wrote:
> > Chris,
> >
> > The motor has a rated RPM at 48VDC, at 66V its RPM will be 66/48

or

> > 1.375 times higher. The motor's rated power is its rated

continuous

> > torque times RPM. At 66V it will produce 1.375 times more power

than

> > its rating. I just don't think that is a good idea for long life
> > reliability.
> >
> > Mariss
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, Chris Baugher
> > <cbaugher_yahoo@b...> wrote:
> > > On Tue, 1 Apr 2003, Mariss Freimanis wrote:
> > >
> > > > Chris,
> > > >
> > > > If you don't ask the motor to go faster than its rated speed

at

> > 48VDC
> > >
> > > Ok, well the max speed is 2100 RPM and the max voltage is

60V. So I

> > > should limit the motor speed to ~1700 RPM? What's the

reasoning

> > behind
> > > that?(I'm not doubting you I'm just curious)
> > >
> > > > and if you don't load the motor past its rated torque then

your

> > 66VDC
> > > > should be just fine.
> > > > The 5V stuff makes it impossible to overload the motor; in

your

> > case
> > > > you'll have to take care not to.
> > >
> > > That makes sense.
> > >
> > > C|
> >
> >
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