"Ballast" Resistors - Pls Check my numbers!?

[JohnnyVegas]

Just want someone to look over my numbers before I order.

I have 3 stepers, 3v 3A each. All Identical.

To start I'm building this board tachus42's 3 Channel Discrete Unipolar Baord.

I am constructing a simple power supply with output at 32.5VDC 10amp.

This board needs a chopper or resistors placed on each motor.
According to my calculations I need:

**7ohm & 63 watts MINIMUM.**

First, is this correct?

Second, the best resistors I found are at digi-key and are $11/pc. I need 2 in series on each stepper. Before I commit can someone check my numbers and confirm my selection?
Link to 3ohm TEH70P3R00JE-ND
And, of course, a 4ohm version in series. 5% tolerance at 70 watts puts me in the 63watt range nicely.

I have been reading and learning so much this past month I think my brain has turned to JELLO!

Thanks so much for anyone whom can help!!!!

[pminmo]

No. Your calculations are incorrect, you need basically 10 ohms at 90 watts. But I can't say that I would advise spending the money to do that. You will wind up with a full step driver that you won't get much speed from without resonating.

[JohnnyVegas]

Since I'm going off your site: Which combination would you suggest?
The power supply is the basic supply plans from your site also.

[pminmo]

Do you have the motor mfg/pn?

[JohnnyVegas]

Originally Posted by pminmo Do you have the motor mfg/pn?

I purchased from HobbyCNC: Middle choice
http://www.hobbycnc.com/products/stepper-motors/
#23-205-DS8 285oz-in bipolar rating, 205oz-in unipolar rating. 3v, 3A, 200 S/R, 2.2mH, Size #23, Dual Shaft, 8 wire

FYI: I have not built the Power supply YET so I am still considering your other version you created. I did, how ever build the entire machine. The electronics are my final stage.
These motors are to get me started. I am planing in the future to really upgrade these to more top of the line when I get over the CNC learning curve.

[pminmo]

Picstep would be the best match.

[JohnnyVegas]

Thanks PMinMO.
I went ahead and began building the 4 axis on your site with the PicSteps.
I completed the 4 axis. Great design BTW.

I tried to register for your website but it wont take my email. It's a hot mail account.

Thanks for the help. Your website was/is a great resource.

Here's a pic of the completed 4 AXIS I just built:

[pminmo]

Really nice looking pcb! What did you use for silkscree/lettering process?

[JohnnyVegas]

Originally Posted by pminmo Really nice looking pcb! What did you use for silkscree/lettering process?

I came up with a DIY approach I never seen anyone use. I took video and lots of pictures of the process. Once I organize them (PICs/Videos) this week I was going to post a tut. The way and method should be easily done by anyone with basic supplies and can also be done on pre-made purchased boards also. Very easy and it seems to come out pretty nice.

Now that I see that it has worked I am going to try another idea on the PicStep board and try to refine it.

[JohnnyVegas]

I put some more pics and things on this thread
http://www.cnczone.com/forums/showthread.php?t=86707

[JohnnyVegas]

Here is another link to my newest screen process for my picstep boards:
http://www.cnczone.com/forums/showthread.php?t=87333