Max rpm for stepper?

[KKamel]

hello all

iw just recieved my new stepper motors and after a bit of test running i can get em up to ~130rpm (400steps per rev).

These are the specs for the motor

Unipolar:
Rated Current 2.0
Phase Resistance 5.0 Ohms
Volt Phase 10V
Phase Inductance 29mH

And i was wondering if this is normal for this kinda motor or is it supposed to go faster?

My driver only does microstepping (400steps per rev) and it is set for 2.0A peak current per phase. Motor is 8wire and wired up as Parallel. Should the current be set as 2.0A or should it be more in the area of 4.0A when wired this way?


Hope you understand my scribbles

edit: Yay running much faster now after some fiddling feel free to give your thought anyhow

[jeffs555]

Generally, bipolar parallel current for an 8-wire stepper motor is 1.414 times the unipolar current. That is why bipolar connection gives higher static torque than unipolar. Static torque is directly proportional to current. However, increasing the current setting will do little if anything toward increasing your speed.

What power supply voltage are you using? Those are relatively high voltage, high inductance motors. Even wired parallel, they would be rated at 7 volts. To get the best speed, you generally need a power supply at least 8 to 10 times the motor voltage rating. In your case, that would be more than 50 volts.

[rexstep]

Steppers are current driven. Think of voltage as the pressure that forces current into the coils because that is it's function in powering steppers. My guess is your voltage is way low. Try a 60 volt supply (driver permitting) and see if your motor gets too hot to touch. If it does, back off to 48 volts and feel it again.

Remember that the main reason steppers lose torque as they increase speed is that it takes time for the current to saturate the coil. The lower the voltage, the longer it takes. Also, speed doesn't count if there's no torque left to push the load so run them nice and warm and you'll be able to get better speed.

But if you're really serious about getting more speed, lose the unipolar driver and drive that 8 wire motor in parallel configuration with a bipolar drive.

RL

[KKamel]

Thanks for your respons, im not after high speed actually im after high torque and low speed. What i wanted to do was just to test the steppers to see if everything was working ok.

The power supply im using is 24V so im guessing that would be a little low then, what effect would this cause? not so high speed and low torque on hogh speed? or will it affect my lowspeed/torque aswell?

im currently running these wired in a parallel connection and the driver is set for about 2amps per phase, is this correct or shall it be set for 4amps per phase?

also i tried running it wired in series however that wasent working well at all, very lowspeed and very low torque, same thing here what should the current be set at? 1.4*2amps?

[rexstep]

Ah, I misread your initial post and thougut you using a unipolar driver.

10 volts is unusually high for a rated voltage since that value is supposed to tell you the minimum amount of volts need to bring the coils to full current. But if you're at 24 volts, that means you are at only 2.4 X the rated voltage which almost certainly is hurting performance. You should probably triple the voltage but it might be cheaper to get a motor with a lower rated voltage and use the power supply you already have.

Now, you're wired in parallel which means you're configured for better high speed torque than low. Switch to series configured and you will have maximized the motor's ability to produce low speed torque voltage issues aside.

-RL

[jeffs555]

For most motors, the bipolar parallel current should be 1.4*unipolar current, and bipolar series current should be .7*unipolar current.

[bunalmis]

For most motors, the bipolar parallel current should be 1.4*unipolar current, and bipolar series current should be .7*unipolar current.

N*I importand factor for the saturations and demagnetization.

How did you find this numeric values?

[jeffs555]

The numbers are based on keeping the DC power dissipation(ie heat) in the coils the same. Power dissipation is equal to resistance times the square of the current. With a bipolar series connection, the resistance is 2 times the resistance of a single coil unipolar connection. To keep the power dissipation the same, the unipolar current needs to be divided by the square root of 2. For the parallel connection, the resistance is half of the unipolar resistance, so you can multiply the unipolar current by the square root of 2 and still have the same power dissipation.

This does not take saturation into account, and that is why I said for most motors. It is true that with these currents, N*I will be higher and if the motor was designed so that the unipolar current was close to saturation then it would be a problem. However most 8-wire motors are designed to handle the higher flux. If you look at specs for most 8-wire motors that list all three currents( unipolar, parallel and series), you will see that they are related by the square root of 2.