Power Supply Voltage

I have a question about the voltage form a power supply and the stepper motor. I've searched the forum and got some hits that seem to pertain to my question, but my electronic skills are limited and i'm not sure I fully understand the info in these posts.
I'm working on my first build and over the years have collected parts for building my own machine. I retired recently and no longer have access to a cnc router. Currently I have a new 70V@ 5A full load automation direct power supply, G203 geckos, 2 Lin Engineering 6.3 amp motors I plan to use. I believe the motors are 48V. Can these be used with this PS? Do the drives control the amount of voltage to the motor? Would I be better off buying a 48V - 12A power supply?

I think you'll need a power supply that can put out more amps. You have to figure that at least two motors will be running at the same time, and at full capacity that would be 12.6 amps, which is a lot more than 5. You'll need at least one more motor for a 3-axis machine; many builds use 2 slaved motors on the X axis. The Gecko 203 drives can handle 80v, I believe, so you'd get best performance out of a power supply that approaches that voltage output. I'm not sure what motors you've got, but you could ask Lin Engineering Stepper Motor Manufacturer | Motion Control | Lin Engineering about them and what power supply they'd recommend, given you're using those Geckos. Usually the voltage marked on a stepper is nowhere close to the amount of voltage they want.

I think the 70v supply will be enough for at least 3 motors. They don't continuously draw the maximum power. What is the motor inductance?

Really? If even one of these motors draws its maximum amperage, that's more than that PS puts out. But often 2, 3, or even 4 motors have to run at the same time in a router. I'm not seeing it working for very long on that PS with those motors.

Thanks for the input. The whole electronic side of the machine is where I fall short on knowledge, but I've gained a good bit from this forum and I believe I have a general idea of how the components work together. What puzzles me is it seems that although a motor is rated at 48V that doesn't seem to be what's required to operate it. Same with current. I plan on having 4 motors (looking for additional to those I have) 2 on the Y, & 1 on the X & Z axis. The LIN's inductance is 2.1mH per phase. It seems that if they were all 6.3 amp they would need over 25 amp to run them. I do understand they don't all run at once or at full capacity so the total amperage can be less. As far as the voltage I'm having trouble understanding how 70 volt can run 48V motors. Does the controller or drive regulate how much voltage is drawn by a motor? Can I run say 2 - 48V motors and say 2 - 24V motors off the same 70V Power Supply? I think I'm going to look for a 48V toroidal with more amps, or should I look for a higher voltage and amperage PS? I see a 63V @15.9A listed on ebay.
I do appreciate your knowledge and input to these possibly not so brilliant questions.
GC

The drivers will drop the 70V down to whatever the motor needs, but will produce more heat as a result. Watch them carefully and reduce power if they get too hot.

I think you will need more current, but could be wrong. Try it and see.

I like using batteries. A stack of 4 12 volt motors in series with a 48 volt "cart" charger and a nice set of fuses would do you good.

I think I'm starting to understand. Another question. The gecko's are rated at 7 amp max. Does that mean that no more than 7 amp can be drawn on the drive or that no more than 7 amp can be connected to the drive from a PS?

The 7 amp rating means that you should not set the current higher than that, otherwise the drive might run hot.

If you want to be very conservative, Gecko's rule of the thumb is to get a power supply rated at 2/3 of the 4 motors' rated current. That's 16 amps in your case. The voltage should be around 45-50v volts for 2uH motors. Your motors might run hot at 70v.

Awerby, in the same way that an arc welder can supply 100 amps from a 15 amp outlet, motor drivers can supply more than the supply's rated current to the motors. The power rating (VA) is what matters.

Drivers are current regulators. 7 amps means it can be set to supply up to 7 amps to a motor without frying. If the power supply can't keep up, then it won't supply as much to the motor. If the motor can't handle what it's being supplied with, it will fry.

I ordered a power supply from Antek yesterday and it's just about exactly what H500 said.
Power 800W
Output Voltage 50V current 16.0A
Now my big dilemma is for a board. I seem to have narrowed it down to the smooth stepper or the PDMX 422 smart bob with a PMDX 134 motherboard for the geckos. With the smooth stepper do you also need a BOB? Any thoughts?

1. The 2/3's number is very conservative. max motor current is drawn if you stall a stepper. When running normal loads we measure about 1/3 of the max current rating. A lot of our power supplies can read and monitor total motor current and the DC volts so its not speculation. It would be highly unlikely to have all three or four moths all stalled at the same time. Voltage gives you RPM (charges the coils faster) and current gives you torque. The Drivers are current limited and allow each pulse to provide the full current BUT power is based on Voltage X current X duty cycle. A short pulse has very little average power in it and motors have electrical inertia so they run on average power. The higher the motor inductance the more voltage you need to get the same RPM (longer it takes to charge the coils with each pulse. That power supply lots of other things will burn up before the power sully even starts to struggle! The good news is it leaves you open for expansion to more drivers and more motors.

2. You did not state the purpose of the table so your choice of the Smooth Stepper cannot be commented on. The ESS is a better choice of this is a shop with other noise sources. In some circumstances it can limit you choices for lower cost THC if this is a plasma or mixed use table.

TOMcaudle
www.CandCNC.com

The table will be a wood router in a home shop. I don't think there would be much in the noise source area, but I could surly be wrong.
Another question: If I use 2 motors to run the gantry back & forth, do both motors need their own drive? I read somewhere about slaving them in mach 3. Not sure what that means.

Quote:

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Originally Posted by shopteacher

Now my big dilemma is for a board. I seem to have narrowed it down to the smooth stepper or the PDMX 422 smart bob with a PMDX 134 motherboard for the geckos. With the smooth stepper do you also need a BOB? Any thoughts?

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You never /need/ a BOB. They just make connections convenient. The stepper driver needs two (maybe three) signals: Step and Direction (maybe Enable).

The average cheap $15 parallel port is more than capable of providing Step and Direction signals for up to 4 axis via the 8 parallel data lines. And even most laptops can provide that. Some have "weak" ports that could use amplification, but why use you nice new laptop when an old WinXP desktop is basically free and will run Mach 3 or whatever better than Win7/8? Same for old desktop with Linux and EMC or Linux CNC or whatever they are calling it this year.

I'm sure the SmoothStepper and other USB based motion control boards can also generate the step and direction signals just fine.

So it boils down to this: You just need to get the signals from whatever produces them to the drivers. Wires do that. If you want to be able to plug and unplug, then you need wires with a connector. The BOBS just makes it easy to connect those wires.

Now, the enable can be a bit trickier as you usually run one enable line to all drivers. And so that one source has to drive 3 or 4 drivers... but even then, it usually works just okfine.

But it blows me away that anyone would pay $55 for the PMDX-134 and then /still/ have to pay for the cable.

Whatever.

Thanks James. You've provided me with a lot of good info in these last couple of posts. I think my lack of knowledge and inexperience is showing through:rolleyes:

Knowledge and experience comes from asking and doing. You're winning just by trying.