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# Thread: Power Requirements

1. ## Power Requirements

I am new to this forum. (ooh nooo!!) I need some help picking the right power supply for my CNC wood router.

My Setup:

I built this 3-axis router 6 feet long and about 1.5 feet wide.

Motors
3 Superior Electric Slo-Syn Stepper motors:
M092-FD09
300 oz/in
2.5v
4.6A
Drivers
3 MBL 536 Bilevel Drivers (Anaheim Automation)
Controller
I am using an embedded controller(uCsimm) that runs embedded linux (uClinux) to send the control signals to the stepper motor drivers. The embedded controller has an ethernet controller built in, so I have the machine in the garage and a 40 foot long ethernet cable that winds its way through my kitchen into a ethernet hub in my office. (I've tripped over this cable a couple times and almost crashed through a wall) . I've also designed a 2D CAD/CAM program using Visual C++. It works fairly good for my setup. All this frustrating work and you know what? I'm not wearing a dress just yet...

My current problem is the following: I was powering the drivers using a 28v switch mode supply and a 5v supply ( the ground of both supplies were tied together as well as the ground from my embedded controller) no filter capacitors. The machine has never runned smoothly, so I want to change over my power supply to a linear mode supply. I'm also looking at a higher voltage 50-70v for the power supply. Can one of you great lads tell me how to go about calculating the power requirement for my setup. I would appreciate it very much...

2. I'm assuming that each phase is rated at 4.6 amps? If so then 4.6 amps times 2.5 volts is 11.5 watts per phase. What are the limits of the drivers?

3. Originally Posted by ViperTX
I'm assuming that each phase is rated at 4.6 amps? If so then 4.6 amps times 2.5 volts is 11.5 watts per phase. What are the limits of the drivers?
Thanks ViperTX,

Yes, the stepper motors are rated 4.6 amps/phase.
The drivers are rated at 10 Amperes/phase max operating current and 70vdc max.

I would like to use a 70 vdc power supply. I am unsure about how much current the power supply needs to supply if I am running 3 motors at the same time?

I read through a white paper on geckos website. Basically, they say to multiple the 4.6 amps/ph times 2/3 to determine the current supply. I come up with a total of 9.2 amps to run three motors. So I would be looking at a 650 watt power supply if I want to supply the drivers with the maximum, 70 volts. Can someone explain the theory to me or give me some formulas ...please

4. Well, I would stay below the driver's maximum voltage say 50 vdc or so. Also since your phase windings have a max amount of power dissipation I would find out what that is....the reason you see so many problems mentioned on this website about burned steppers and drivers is that everyone is exceeding the limits of both devices and waiting until something burns up.
The only thing that extends the time before you run into problems is the PWM that the drivers use....so your maximum power dissipation is only achieved for some small amount of time...but eventually you do hit that "gotcha" time.

5. If you take each phase at 4.6 amps and you have 2 phases per motor and 3 motors....then theoretically your total current requirements are 9.2 amps per motor times 3 motors = 27.6 amps....take 2/3 of that and the result is that your supply should be able to supply about 18 amps...if you intend to build your own supply let me know....cause there is some other stuff to be aware of.

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