Question about behaviour of stepper motors

hello

I am new to the world of 3 printers.
I tried to use ramps with arduino and marlin firmware, and I began to give a command in manual mode to one of steppers. I tried both repetier host and pronterface.
I used my multimeter to see the current that one of phases of the stepper will draw.
I found that, the motor nearly does not draw significant current while rotation, and it usually draws a sigificant current when stops!
actually, when it stops, one time it drew 0.8 amps with making noise, and another time 1.25 amps with making noise(nothing changed, load is the same!), and even some times the meter gives me 0 with no noise at all, so the stepper draws 0 current at standstill.
I do not understand, is this correct? what is the correct behaviour of stepper that I send a manual command to it using repetier or pronterface?

For a good guide to how steppers and stepper drives work, have a look at this document from Gecko.

Your multimeter may not be showing anything meaningful measuring the high frequency current flowing through the stepper winding.

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Originally Posted by snowyskiesau

For a good guide to how steppers and stepper drives work, have a look at this document from Gecko.

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thanks for the materials!

thanks for clarification.
My motor is 1.7 A per phase, and the driver is 1 A max (without heatsink), so I wanted to check how much current the motor draws.
are not there any practical way to know how much current is drawn by the motor?

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Originally Posted by mamech

are not there any practical way to know how much current is drawn by the motor?

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Probably the best you can do is measure the driver supply current. That will give you the average motor current (plus any losses within the driver). Is there a particular reason you want to measure the current?

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Originally Posted by CitizenOfDreams

Probably the best you can do is measure the driver supply current. That will give you the average motor current (plus any losses within the driver). Is there a particular reason you want to measure the current?

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good idea, thanks.
yes, I have a reason. I want to use the driver to supply 2 motors instead of 1, so I wanted to be sure that the current drawn is below the maximum limit of the driver

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Originally Posted by mamech

I want to use the driver to supply 2 motors instead of 1, so I wanted to be sure that the current drawn is below the maximum limit of the driver

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I would say it is not a good idea to connect two motors to the same driver. Especially when the driver is rated at 1A and the motors are rated at 1.7A each. Any reason you cannot add a second driver?

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Originally Posted by CitizenOfDreams

I would say it is not a good idea to connect two motors to the same driver. Especially when the driver is rated at 1A and the motors are rated at 1.7A each. Any reason you cannot add a second driver?

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There are 2 reasons in fact:
1) the load on motors is very low, so they will never draw the peak current (or may be I am wrong?)
2) this design is a part of a product, so each component out means lowering the price of the product (unless it is obligatory component, which is what I am trying to know currently)

When running 2 stepper motors in sync there are 2 methods that I would consider. Both procedures use 2 stepper drivers, each attached to a single motor. From here you can either combine the step and direction inputs on the drivers, or use another available step/dir output or each, but slave one to the other in the control software.

The benefit of the first is that it only uses one step/dir output from the computer. If one motor runs the wrong direction, switch the wires on ONE phase to reverse the direction.

The benefit of the second is that the individual motors can each be "homed" and reversing of the motors can be done in software.

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Originally Posted by 109jb

When running 2 stepper motors in sync there are 2 methods that I would consider. Both procedures use 2 stepper drivers, each attached to a single motor. From here you can either combine the step and direction inputs on the drivers, or use another available step/dir output or each, but slave one to the other in the control software.

The benefit of the first is that it only uses one step/dir output from the computer. If one motor runs the wrong direction, switch the wires on ONE phase to reverse the direction.

The benefit of the second is that the individual motors can each be "homed" and reversing of the motors can be done in software.

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so do not you think it is reasonable idea to use 1 driver, as long as load torque is light on both motors, and the overall current will not exceed maximum?

All you can do is try. If it doesn't work you have these options.

With 3d printers it is quite common to run two motors on one driver on the Z axis.
At 1 amp your drivers are less than normal but may be usable if you are driving a fine screw such as M5 x .8 on the Z axis.
Wire them up in series so driver will deliver up to 1 amp to both motors. In parallel you could only provide 1/2 amp each..
Motors are limited in top speed with series connection but this is not a problem with z Axis.

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Originally Posted by george4657

With 3d printers it is quite common to run two motors on one driver on the Z axis.
At 1 amp your drivers are less than normal but may be usable if you are driving a fine screw such as M5 x .8 on the Z axis.
Wire them up in series so driver will deliver up to 1 amp to both motors. In parallel you could only provide 1/2 amp each..
Motors are limited in top speed with series connection but this is not a problem with z Axis.

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thank you very much for your answer.