G203V Power Requirements

[Big John T]

I have G203v drives and the steppers are 2.8A/phase and 3.08 volt. I'm looking at an Antec power supply and there is two choices near what I want. A 56 volt and a 63 volt. The 56 is 18.18 times the stepper rating and the 63 is 20.45. I'm building a plasma cutter so speed is the need not power.

Is the 56 volt the better choice for this application?

If I use three of these steppers the total is 8.4 amps.

Is the 600 watt plenty big?

Thanks
John

[Richards]

Either power supply should work just fine. The 63VDC power supply would give just a little more speed and a little more heat, but, I really don't think you would notice the difference. I have used a Variac on my 70V power supply to lower the voltage while testing different motors. One thing that really surprised me was that lowering the voltage 10% or so had very little real effect on the motor's performance. My feeling is that if you need to tweak the power supply/motor combination to get the last bit of speed or the last bit of torque that you would be better off getting a bigger motor. Normally, I like to size the motor and power supply so that I can use about 15X the motor's rated voltage. Then I like to size the motor so that I can run the motor at 500 to 1,000 RPM (with a belt drive transmission). With the Oriental Motor stepper motors and the G202 and G203 stepper drivers, that gives me excellent reliability and excellent performance.

[Big John T]

Thanks for the reply Richards. Interesting that you noticed little or no change in performance for a 10% drop. I had a conversation with someone at Gecko that was very knowledgeable on the subject. He gave me the same sort of info that once you reach a point any increase in voltage is negligible in performance.

He told me to get the voltage needed empirically to take a 24 volt power supply and find the fastest speed that the heaviest loaded servo will go then do the following math to arrive at the desired voltage for the supply.

(Speed you want/(Speed you got * .9))*voltage used = voltage needed

John

[Richards]

Here's another forumula that Mariss posted that computes the maximum voltage that you should use depending on the inductance of the motor: Voltage < 1000 * SQRT(inductance)

As an example, one of the Oriental Motor PK296A2A-SG3.6 motors that I normally use is rated at 1.5mH inductance per phase. Using the forumla, 1000 * SQRT(0.0015) = 38.73 Volts MAXIMUM. I've run that motor on power supplies ranging from 27VDC to 35VDC with perfect results. Another motor, the PK299, is rated at 6mH per phase, so 1000 * SQRT(0.006) = 77 VDC MAXIMUM. I run that motor with a 70VDC power supply. It works perfectly. A third and final example is the PK299-F4.5 motor that is rated 2.5mH, so 1000 * SQRT(0.0025) = 50VDC MAXIMUM. I've used that motor with power supplies ranging from 35VDC to 45VDC with perfect results.

NOTE: Not all motors are created equal. The Oriental Motor stepper motors have been perfect for all of my applications, but I've had very limited experience with other brands of motors. If you use this formula and your motor seems to be excessively hot, turn down the voltage until the temperature is acceptable. Stepper motors are designed to run hot, but there's no need to stink up the place with fried insulation. My motors are rated to withstand an 80 C. temperature rise. For my own purposes, I limit the temperture rise to 60 C. So far, I've never lost a motor (and I've had dozens of them chugging away for over fifteen years).