I picked up a pair of Nema 34, 637 oz./in. steppers off ebay which I will either use to upgrade the Nema 23's I currently have on my router now or use for a new project in the future but I am wondering what size power supply I should get?  The motors phase current is 6.3A.
I am thinking I will use a 48VDC switching power supply but not sure what amperage it should be.  I have seen some good deals on 48V/5A supplies but not sure if one of them would be adequate to run two motors.  Perhaps one for each motor?

Any ideas fellas?


Carl 

Build your own, Bob Campbell has a good article on how to do this and work out what you need.
You will find it here http://www.campbelldesigns.com/files/power-supply-part-1.pdf

Hood

Thanks Hood.  That is a very good article. Building your own power supply seems like it could be more expensive then buying a ready made one though, since you have to buy all the seperate components.  The Toroidal transformer I would imagine is not under $30.00?  The 48V/5A switching power supplies I was looking at were $30.00.  I guess it all depends on what size power supply would be best for my motors and whether one was available ready made or I need to build one to get the exact specs I need to get the most out of the motors.

The one problem I have at the moment is that I am not sure what is the voltage of the stepper motors.  I don't have them in my hand yet since they haven't come in and the the data sheet on them doesn't list a specific voltage.  It just shows a chart that shows the Torque and the speed at given voltages (24vdc, 45vdc & 75vdc).

Here is the datasheet.  It is model M-3431-6.3 http://www.motionsolutions.com/images/size%2034%20motor%20&%20encoder.pdf

Watch what you are doing with switching power supplies, some drives dont like them.
 The voltage of your steppers is really not important as you will be wanting to supply a lot more volts than what they are rated at, I think the usual figure is min 5x max 20x, most steppers I have seen are 5V.
 You are best to run steppers on as high a voltage as your drives will allow.
Hood

You can run them at any voltage between 24 and 75.

You will need 6.3A per phase per motor so 6.3A * number of phases * number of motors = size of power supply. (roughly)

Graham.

I plan on using Gecko 201 or 202 drives.  Depending on which ones I find at a good price. 

Also my motors are 4 wire so does that mean they have 2 or 4 phases?

Carl

If your using Geckos, the required current per motor would be 6.3 x 2/3, or 4.2 amps per motor. See the Gecko docs.

Now what do you do when the motors you use don't all have the same specs?  Do you use the same formula when trying to figure out
the power supply required?  For example I have two of the motors that I listed below but I am looking for one more Nema 34 motor that has about the same holding torque but it is doubtful I will find one with the exact same specs unless I try and purchase a new motor direct from the manufacture at a much higher cost.

So if I use the formula mentioned further below,  6.3A * number of phases * number of motors = size of power supply, for the first two motors do I just take the same formula and use that for the third motor and add the two totals together?

Thanks,
Carl

Heres what Gecko have to say about it.
"The easiest factor in choosing a power supply is its current rating. The current rating of the supply
is based on your motor choice. The drive will always draw less than 2/3 of the motor’s rated
current when it is parallel (or half-winding) connected and 1/3 of the motor’s rated current when it
is series (or full-winding) connected. That is to say, a 6 Amp / phase motor will require a 4 Amp
rated supply when parallel connected and a 2 Amp rated supply when series connected. If
multiple motors and drives are used, add the current requirements of each to arrive at the total
power supply current rating."
Hood

Ahhhh.  Ok...  Now do you take that Amperage value and multiply it by the number of phases?

For example.  If my motor is rated at 6.3A per phase and I take 2/3 of that value, gives me 4.2A per phase in Biploar parallel but the motor has two phases so do I multiply 4.2 by 2 giving me 8.4A for that one motor?   Is this correct or do I just take the 4.2A as my value for the one motor?

Sorry for so many questions but with my first machine I just used a 24VDC power supply which is under rated voltage wise for the steppers I was using.  This time around I want a power supply that will get me the max performance out of my motors but going with more power doesn't leave me much room for error. 

I just picked up the third and final motor off ebay so now I can go ahead finalizing power supply requirements.  It's a PacSci Powerpac Nema 34 , 3.3A Bipolar series, 65V, 97W.  It's an 8 wire motor so I need to decide if I am going to connnect them in Bipolar series or parallel.  Can't remember which one is better.  It's been awhile since I did this with my other machine so I have forgotten alot that I learned.

Thanks for all your help everyone.  I would really be up a creek without a paddle if it wasn't for people like you guys.