Stepper Power Question

[Cartierusm]

OK, so I'm building an automated machine for a specific operation and I'm going to use a stepper motors as I can control speed and location accurately.

Now I know if you up the volts you get better torque at higher speeds. SO what if I'm only going to be moving the stepper at 3 RPMs? What voltage would I need.

I'll be using 850 oz. in. stepper motors and probably wired bipolar parallel and use an inexpensive Probotix driver. At 3 RPM what oz in would I get and what power supply should I use?

[irving2008]

Originally Posted by Cartierusm OK, so I'm building an automated machine for a specific operation and I'm going to use a stepper motors as I can control speed and location accurately. Now I know if you up the volts you get better torque at higher speeds. SO what if I'm only going to be moving the stepper at 3 RPMs? What voltage would I need. I'll be using 850 oz. in. stepper motors and probably wired bipolar parallel and use an inexpensive Probotix driver. At 3 RPM what oz in would I get and what power supply should I use?

it all depends on the speed/torque curve of the steppers. The reason for running higher voltages is to push more current through the inductive reactance of the motor winding earlier in the step and so move the 'knee point' of the curve further to the right (maintaining torque at higher revs). Without the speed/torque curve and the motor specifications (inductance/resistance) its impossible to say, however the data sheets I have suggest that you should typically get 80 - 90% of the holding torque below 500 steps/sec on a big motor, thats 2.5 rps or about 180rpm...

[Cartierusm]

What kind of PS, since i'm not going for high speed can I get that torque with a 24V 6A? I'm trying to get all the torque I can, but don't want to spend a ton of money.

[Mariss Freimanis]

For 3 RPM, wire your motor in series and use as low of a supply voltage as the drive mfg permits. This will keep your supply as small and inexpensive as is possible. Your speed is so low that voltage will have no effect on performance.

Mariss

[Cartierusm]

Thanks, I was always unsure about voltage pertaining to torque.

[Mariss Freimanis]

Voltage determines how 'quickly' current can be injected into and removed from a winding. 3RPM is 20 seconds per revolution which means you have 4 tenths of a second to inject and remove current. That is an eternity in electronic terms.

Current determines torque. At this speed the required current is reached in a few thousands of a second, it stays there for the 4/10 seconds and is then removed. The time spent injecting and removing the current is a tiny percentage of this time at such a low speed.

That is why I recommend you wire the motor in series. A series connection requires half as much current from your supply as a parallel connection. Your supply has to only half as big as for a parallel connection. There are no drawbacks at 3 RPM.

Mariss

[Cartierusm]

In another thread in this section someone said this,"Make sure that the motor is wired bipolar parallel. I suspect that even the 4 wire motor is wired serial and that will kill the low speed power. Remember that the torque ratings are holding torque and the torque will drop off as soon as you move the motor. If you are using a 7/8" x 6tpi acme rod you will not have enough torque."

I know this is a different application but will wiring in series kill the low end torque? Thanks.

[Mariss Freimanis]

Torque = Amps times the number of turns of wire it passes through. In series, amps pass through twice as many turns of wire as it does in parallel. Only half as much current is needed for the same torque.

Mariss

[Cartierusm]

Thanks.

[TOTALLYRC]

Originally Posted by Cartierusm In another thread in this section someone said this,"Make sure that the motor is wired bipolar parallel. I suspect that even the 4 wire motor is wired serial and that will kill the low speed power. Remember that the torque ratings are holding torque and the torque will drop off as soon as you move the motor. If you are using a 7/8" x 6tpi acme rod you will not have enough torque." I know this is a different application but will wiring in series kill the low end torque? Thanks.

Hi, That was me.

Originally Posted by Mariss Freimanis Torque = Amps times the number of turns of wire it passes through. In series, amps pass through twice as many turns of wire as it does in parallel. Only half as much current is needed for the same torque. Mariss

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