Need Help!- Steppers Volts and Amps How Many How Much

[Mr.Chips]

I see a lot of steppers out there, many are not specifically designed for CNC, so some of them have very attractive prices.

I’m looking for a stepper in the range of 400 oz/in.

My PS puts out 35V and
My Driver cards have these specs
.5-2.5 Amp Current Limiting
8V - 32V Supply
Unipolar Style

What would be the Min and Max Stepper Voltage spec I should look for?

What would be the Min and Max Stepper Amp spec I should look for?

Thanks

[ger21]

For best performance, get as close to 2.5 amps as possible and the lowest possible voltage. You want the highest current at the lowest voltage. Lower voltages give better performance, but as amps go down, volts go up.

[Mr.Chips]

Originally Posted by ger21 For best performance, get as close to 2.5 amps as possible and the lowest possible voltage. You want the highest current at the lowest voltage. Lower voltages give better performance, but as amps go down, volts go up.

Thanks Gerry

"as amps go down, volts go up"
Do you mean that in general a .5 amp stepper will require 100V for it to work effecently?

[ger21]

You want to run it from 10-20 times the rated voltage.

[pgconcepts]

I'm looking into purchasing a new stepper controller board and new steppers to boot. I'm looking at Unipolar, 2.4V 2.4A 1.5mH at 6000g/cm, which I take as about 530oz/in.

this is the link to the ones I already have:
http://www.jameco.com/webapp/wcs/sto...oductId=237543
They're about 265oz/in, but at 12V 0.38A and 30mH =/

Using the steppers in the link above, I have a 24V PSU, but since they're 12V steppers, I assume their inductance, 30mH, really hampers their torque at high-speeds.

here is the link to the new ones I'm looking at getting:
http://www.jameco.com/webapp/wcs/sto...oductId=237569

If I were using the new steppers, I would assume a drastic change in performance; however, I'm concerned about heat, if I were to run with 24V. A question comes to mind about this. The motors are directly connected to the driver without any other components wired to protect the motor from the voltage surging through at the much-greater-than-rated voltage? I'm hoping it's that simple.

[pminmo]

265ozin ? By my calculations they are around 42ozin. http://www.onlineconversion.com/torque.htm
If you buying new motors, consider some of these for around the same price:http://www.kelinginc.net/SMotorstock.html
Keling has about the best prices around.

[pgconcepts]

Thank you, pminmo. I think I can see where my calculations went wrong. I multiplied the ounces by the cm to inch conversion when I should have divided. The result is very close to what the online conversion calculator says... Seems like it should be exact, which is a bit worrisome for me.

grams / 454 = pounds
pounds * 16 = ounces
cm / 2.54 = inches
ounces / inches = what I hope is the right answer

I'm running a 4 TPI leadscrew, which turns very freely, but because of the coarseness, I believe torque is very important to prevent missed steps. I'm using a Dremel for the cutting head, which works fine... it would work better if I could traverse much faster to actually make a complete pass in a reasonable amount of time.

I think if I were to purchase some bipolar motors off the link you suggested, what would be a good driver for them? I'm thinking of buying a kit off of hobbycnc.com. What do you think?

I think just about any of the motors on the link you supplied would make a night and day difference on the performance of my machine.

[pgconcepts]

I think (3) of these steppers: http://www.kelinginc.net/KL23H276-30-8A.pdf
would provide me more than what I hoped to achieve, especially if I were to use this PSU: KL-320-36 36V/8.8A on this page:
http://www.kelinginc.net/SwitchingPowerSupply.html
These steppers offer a nice torque curve:
http://www.kelinginc.net/KL23H276-30-8AT.pdf

Each stepper is rated at 3.0A running in Unipolar mode.
I would assume that the very short burst of running all 3 axis would be fine if they really do pull a full 9A altogether. This would very rarely happen, but it would be nice to have the option of running them all continuously and simultaneously while never having to worry about over-stressing anything.

I'm on a tight budget, so I'm looking at this controller:
http://www.hobbycnc.com/products/hob...er-board-kits/

Has anyone had success with this board kit?
I'd like to hear any opinions about this configuration (Steppers, Board, PSU) or any other suggestions would be equally appreciated.

[MonoNeuron]

I have used this board and it's not too bad. It's not high speed but it's also not way too expensive for you. It uses the same drive chips that some photocopiers use so they can't be too bad. Remember, you get what you pay for but this drive is okay for what you want it for. I would use a 5-6 amp drive for the steppers as they don't see full power all the time. You could probably get away with a 4 amp supply. (at a pinch.)
Rich.

[pgconcepts]

Thanks, MonoNeutron, this board sounds better now with hearing some testimony. I'm curious about how many pps I can get out of it, since you say it isn't high-speed. I figure 1000-2000 pps is plenty fast enough for anything I'll do with this machine, if 200pps constitutes 1 rev on a 4 phase motor. (Can someone please kindly explain to me how that really works if it's different?)