How find the rated current of stepper motor without datasheet

Hi,
I have some stepper motor recoverd from old printers and scanners but I not find the datasheet.

For a correct driver setup I need to know the rated current: VREF = Rated motor current x 8 x Rsense,
but without a datasheet I not know it.

There is a way to find it with some tricks or measurements?

Thank you so much

i guess you're trying to determine the current for a power supply

if you know the voltage, you can measure the resistance and from that ~current. use that as the basis

gcjr:
i guess you're trying to determine the current for a power supply

if you know the voltage, you can measure the resistance and from that ~current. use that as the basis

Yes also but first to determine the Vref to setup correctly the A4988 driver.

Without the datasheet I not know the voltage, I find the wires for the two windings but for voltage and rated current I not know how can I do.

One motor is from a scanner with a 12V power supply so this means the motor probably work at 12V?

what do you mean by Vref?

One motor is from a scanner with a 12V power supply so this means the motor probably work at 12V?

probably

I mean the one i set by rotate the potentiometer on the driver, like the attached image

a4988.jpg

gfucka:
I have some stepper motor recoverd from old printers and scanners but I not find the datasheet.

Do you have any info about the voltages used by the printers?

If not I think all you can do is guess the current. You can measure the resistance of the motor coils. If the resistance is high (for example 30 ohms) then the current is probably low - of the order of 300mA. If the resistance is much lower (say 3 ohms) the current is probably about 1amp to 2amps.

All you can do is start with a very low current setting on the driver - the lowest that will get the motor working - and then gradually increase it while keeping an eye (a finger?) on the motor temperature. It would not be unusual for stepper motors to operate at a temperature at which they are uncomfortable to touch for more than a few seconds. The motors on my 3D printer get warm but I have never noticed them so hot as to be uncomfortable to touch.

...R

gfucka:
Hi,
I have some stepper motor recoverd from old printers and scanners but I not find the datasheet.

For a correct driver setup I need to know the rated current: VREF = Rated motor current x 8 x Rsense,
but without a datasheet I not know it.

There is a way to find it with some tricks or measurements?

Thank you so much

Try a DC current through one winding, gradually increasing in 10% steps until the stable motor temperature is about 50C hotter than the environment? Steppers are usually rated for a particular temperature rise. It takes a long time to stabilize in temperature so allow 5 to 10 minutes for temperature stabilization before each increase in current.

For low-duty cycle motors such as used in domestic printers and scanners the max rated current will probably be somewhat higher than this, as its assumed the thing is used occasionally only.

Robin2:
Do you have any info about the voltages used by the printers?

If not I think all you can do is guess the current. You can measure the resistance of the motor coils. If the resistance is high (for example 30 ohms) then the current is probably low - of the order of 300mA. If the resistance is much lower (say 3 ohms) the current is probably about 1amp to 2amps.

All you can do is start with a very low current setting on the driver - the lowest that will get the motor working - and then gradually increase it while keeping an eye (a finger?) on the motor temperature. It would not be unusual for stepper motors to operate at a temperature at which they are uncomfortable to touch for more than a few seconds. The motors on my 3D printer get warm but I have never noticed them so hot as to be uncomfortable to touch.

...R

Thanks for answer

One motor is from scanner with 12V power supply. If I know the voltage can I calculate the current?

I will measure the coils resistance and then let you know.

Do you mean if I "burn" mi finger it means the current is to high?

MarkT:
Try a DC current through one winding, gradually increasing in 10% steps until the stable motor temperature is about 50C hotter than the environment? Steppers are usually rated for a particular temperature rise. It takes a long time to stabilize in temperature so allow 5 to 10 minutes for temperature stabilization before each increase in current.

For low-duty cycle motors such as used in domestic printers and scanners the max rated current will probably be somewhat higher than this, as its assumed the thing is used occasionally only.

Do you means without a driver? So direct to winding?

At what voltage?

gfucka:
Do you mean if I "burn" mi finger it means the current is to high?

Yes.

The notion of 50C hotter than ambient in Reply #6 is more precise.

...R

All the motors I have salvaged have had some form of marking on them.

From that it is often a simple process to google and find a datasheet or somebody else who has used it for a new application.

Sometimes you may have to use the numbers on the motor but omit something from the leadin or trailing parts of the numbers to get going as they can be parts of a specific use code.

Throw the numbers in here or a good focused picture...or both ;D

Here some photos of recovered motors without datasheet.

After I will post others

Thanks

Images from Reply #11 so we don't have to download them. See this Simple Image Posting Guide

...R

gfucka:
Do you means without a driver? So direct to winding?

yes

At what voltage?

No, set the current, not the voltage. You need an adjustable current bench power supply to do this.

Please can you explain me what exactly is adjustable current bench power supply??
Thank you

Its a bench power supply with both adjustable voltage and current-limit controls. If you don't have one you can't do this.

Most bench power supplies are like this. If the load tries to draw more than the set current limit the voltage drops to prevent the current exceeding the limit. Very useful.