stepper motor drives for high amp

[newguy]

Im new here so take it easy on me if i sound stupid. Anyway i have three slow syn unipolar stepper motors i came across that have the following specs.


2.64 volt
5.5 amps
450 hold oz ( thats a lot of torque )

Looking around i can find somewhat inexpensive drives for low amp but nothing for this high of amperage. I see there is a schematic for a higher amperage drive on this site that can be built somewhat inexpensively and ive built my own curcuit boards a time or two before but they never come out very good . ( they work , well sometimes they do ) Does anyone know of a fairly inexpensive route that i could get some drivers for these motors? Also if anyone here might have an excess of drives that will work on these i can come up with more of these motors and maybe we can work out a trade or something.

[balsaman]

Sell the steppers on ebay. Buy some that will work with a cheaper drive. What sort of machine you building?

Eric

[newguy]

4 foot by 6 ft router but i figure if i design it properly ill be able to use just about anything as the machine head. And as for selling them on ebay i thought about that but i would also like to take some of these motors and use them to make my lathe and possibly my mill cnc hence the need for torque.

[Mariss Freimanis]

Sounds like you have some M093-FD11 steppers. Those are excellent motors; hang on to them.

Mariss

[newguy]

yes those are the motors , pretty pricey to my understanding but i got them for pretty much scrap metal prices, along with some hardened rods and sleeve bearings.

[Chagrin]

Stepperworld.com's FET-3/4 is capable of handling up to 15 amps.

[balsaman]

I doubt it. The FETS are RATED at 15 amps, but there are no heatsinks, and no room for any. Also, the circuit board can't handle that kind of current. Also its a unipolar board, so the current limiting resistors needed to get any kind of perfomance would be HUGE. Gecko's are the only cost effective drive for those motors IMHO. You're looking at $345.00 plus powersupply. You would have a nice motor setup mind you.

I would build first, worry about the drive last.

Eric

[rvan]

Check out http:\\www.Stepper3.com

They sell:
(S3HPPWM) 3 AXIS 8 Amp Pulse Width Modulated Stepper Motor Driver

for $369.00 for three axis. Considering that you would need to buy three separate geckos at least $114, its reasonably priced. Note Gecko only sells Bipolar and Servo drives. Although you could use Gecko Bipolar drives to power Unipolar steppers, they will only operate under a fraction of their speed and torque capabilities.

With this board, you do not need power resistors to drive unipolar steppers. Its also allows you to use separate power supplies for each motor (see the user's manual for details), output power is controlled using on-board potentialmeters.

[ger21]

Although you could use Gecko Bipolar drives to power Unipolar steppers, they will only operate under a fraction of their speed and torque capabilities.

I believe that this statement is false. I've never seen anyone who has used both bipolar and unipolar drives recommend the unipolar drives. It seems like bipolar always gives better performance.

Its also allows you to use separate power supplies for each motor

I read the manual, and to calculate the current for the power supplies, you need to take the current rating for each phase of each motor, and add them together. So, (5.5 + 5.5) x 3 motors=33amps MINIMUM. Geckos, on the other hand, are much more efficient, only needing 2/3 of ONE phase rating for each motor. (5.5 x 2/3) x 3 = 11 amps MAXIMUM. This smaller power supply could save you quite a bit of money.

Another thing is that the Gecko 201's have 10x microstepping, versus 1/2 step for the Stepper3. With microstepping, you'll get much smoother running motors.

I'd keep the motors and buy Geckos.

Hopefully Mariss or someone else will step in and provide a more eloquent explanation.

[radio-op]

I'll give it a shot.
The highest torque is developed in bipolar mode due to the fact that the full length of each coil in the stepper are always energized. Whereas in the unipolar mode, the center tap on each coil is used and only 1/2 of each coil is energized.
As to the question of a bipolar drive and a unipolar motor, that is partly true. You can wire a unipolar motor(6 or 8 wire)as a bipolar, but you can not wire a bipolar motor (4 wire) as a unipolar. A bipolar drive will only drive a bipolar motor and a unipolar drive will only drive a unipolar motor. An 8 wire motor can be more useful because it will allow you to configure the most modes.
Rvan you are correct that a PWM or chopper drive is more efficient then a linear drive. In order to control current flow, a linear drive will require a bias resistor. The size will be dependent on the Voltage and the current rating of the motor. With the high current motors discribed, the resistor or network would be in the 300-400 watt range. A quick check at Digikey will show that to handle that much power will cost a arm and a leg.
By and large the most cost effective and powerful setup would be a bipolar chopper or PWM drive system.
Hope this helps,
Bill

[Mariss Freimanis]

If it helps, you can use the following as a means of calculating how much bang you get for your buck. It applies as a rough measure to all drives you may be considering:

Value = (Max Amps times Max Supply Voltage) / Price

Example: G201 is (7A times 80VDC) / $114 = 560 / 114 = 4.91

The bigger the number, the better the value for your money. Try this on some other drives and see what number you get.

Another one might be (2Amps times 36V) / $35 = 72/35 = 2.06

You are getting about 40% for your money with that one.

This number does not take into account microstepping, midband compensation and other factors that enhance a drive's utility.

Mariss

[ehiebert]

Value = (Max Amps times Max Supply Voltage) / Price

Hey that's a pretty reasonable value formula. It works out to power delivery per dollar. I like it!!


Eldon.