Stepper motor current calculating

[m_c]

I'm finally getting around to resurrecting an old engraver, but have drawn a blank on a suitable datasheet for the Z-axis stepper motor.

It's a Japan Servo KP46BM2-017.

The label says it's DC6V, and 30 Ohms.
Would I be correct in assuming the required current will be 0.2A (6/30)?

[JohnHaine]

Sounds way too low, would expect at least 1 amp. Are you replacing the drivers?

[m_c]

That's why I'm questioning it.
It is only a small pancake motor, so 200mA could be about correct.

Once I get the bench cleared, I'll stick 6V through a coil and see how much current flows.

[m_c]

Done a bit testing earlier, and it appears the numbers are about right.
Applying 6V results in 190mA flowing, so not that far of the calculate 200mA.

It also makes the motor noticeably cog when turned by hand while under power, and after connecting up the original control box, the amount of cogging feels very similar.

It does mean my plan to use some basic enclosed TB6600 drives won't work, so I'll have to go for something even smaller.

[Robin Hewitt]

The Voltage written on a modern stepper is usually down around 1 Volt. They don't expect you to use 1 Volt, they expect you to use maybe 36V to overcome the coil inductance and then limit the current so it doesn't go pop.

There was a time, long ago, when people used the L200 stepper driver chip and 6 or 12V steppers were quite normal.

If you can turn the motor with 6V applied then maybe you have coils in series? Even then it doesn't sound at all right.

[m_c]

Robin, it's only a very small pancake motor from the 90s I'd guess.
It's only a 4 wire motor, and I only applied power to one pair at a time.

I'd guess torque will be measured in fractions of Ncm. It's only moving the Z-axis on a small engraver, so not that much torque should be needed.

[JohnHaine]

Does it look like this one: https://i.ebayimg.com/images/g/1jgAA...j/s-l1600.webp ?

That looks like a standard hybrid stepper to me with 2-phase winding rather than "pancake" type.. If you check the 4 wires they should be in 2 pairs, each pair having a resistance of 30 ohms. The significance of the DC resistance is that it determines how much power is dissipated in the windings, not how much current is needed or how much torque is generated. Assume that you'll need ~1A per coil. Use a modern driver (preferably not the 6600). When driving with the correct current it should be virtually impossible to turn the rotor by hand. I usually get drivers from Stepper Online, they have a good range at reasonable price.

https://www.omc-stepperonline.com/stepper-motor-driver .

Modern stepper drivers, apart from allowing microstepping, allow you to operate the motor at a higher voltage that gives better acceleration etc. The driver acts like a switch mode power supply stepping down the supply voltage to obtain the rated current. This also means that if you set the coil current to say 1A the supply current is significantly less. Because this motor is quite old and has a high coil resistance you could probably use a 36V or even higher supply. You'll see that the drivers allow you to set the current limit - start low and increase it until you are getting enough torque and the motor can run fast enough/give enough acceleleration. Steppers can happily run quite hot (but not hot enough to burn you!).

[m_c]

Does it look like this one: https://i.ebayimg.com/images/g/1jgAA...j/s-l1600.webp ?

That looks like a standard hybrid stepper to me with 2-phase winding rather than "pancake" type.. If you check the 4 wires they should be in 2 pairs, each pair having a resistance of 30 ohms. The significance of the DC resistance is that it determines how much power is dissipated in the windings, not how much current is needed or how much torque is generated. Assume that you'll need ~1A per coil. Use a modern driver (preferably not the 6600). When driving with the correct current it should be virtually impossible to turn the rotor by hand. I usually get drivers from Stepper Online, they have a good range at reasonable price.

https://www.omc-stepperonline.com/stepper-motor-driver .

Modern stepper drivers, apart from allowing microstepping, allow you to operate the motor at a higher voltage that gives better acceleration etc. The driver acts like a switch mode power supply stepping down the supply voltage to obtain the rated current. This also means that if you set the coil current to say 1A the supply current is significantly less. Because this motor is quite old and has a high coil resistance you could probably use a 36V or even higher supply. You'll see that the drivers allow you to set the current limit - start low and increase it until you are getting enough torque and the motor can run fast enough/give enough acceleleration. Steppers can happily run quite hot (but not hot enough to burn you!).

This was definitely an older pancake motor, and not a modern hybrid stepper like your link.

I can't remember the exact drive I ended up using, but it was one of the small ones favoured by makers/3D printer DIYers, and set it as low as possible.
First one did stop working after not much running, which I thought was possibly down to the motor being high inductance, but it's replacement has been running fine when needed, so possibly just a bad driver to begin with.

I should maybe create a thread with the build, as I should really rework the 'temporary' stripboard I used to interface the stepper drivers to the DDCSV controller.