# what is phase resistance in stepper motor & how it is useful?

#### VETRIVEL MURUGAN

Joined Jul 23, 2021
12
it should be high or low.
I need higher running torque motor.
what should I choose high resistance or low resistance in motor for high torque

#### Ian0

Joined Aug 7, 2020
3,238
Simply the resistance of each winding.
Torque is proportional to the current * number_of_turns. The lower the current the more turns you can pack in.
That means that torque is about the same for all motors with the same frame size.
The difference is the inductance which varies with (number_of_turns)^2
High resistance means you need more voltage to drive it.
High inductance means that the L/R time constant is longer so the maximum rate of change of torque is lower.

#### VETRIVEL MURUGAN

Joined Jul 23, 2021
12
Simply the resistance of each winding.
Torque is proportional to the current * number_of_turns. The lower the current the more turns you can pack in.
That means that torque is about the same for all motors with the same frame size.
The difference is the inductance which varies with (number_of_turns)^2
High resistance means you need more voltage to drive it.
High inductance means that the L/R time constant is longer so the maximum rate of change of torque is lower.
This means I need to choose low resistance & low inductance. am I right?

#### Ian0

Joined Aug 7, 2020
3,238
This means I need to choose low resistance & low inductance. am I right?
If you have a low supply voltage and you want it to go fast! But it does mean you need a high current driver.
The most important choice on stepper motors is bipolar vs. unipolar. You can get a lot better performance out of bipolar, but the drive circuit is much more complicated.
You can drive two 75Ω/12V unipolar stepper motors from a single ULN2803, and they will work quite well. Driving a 5Ω bipolar motor of the same size will require a specialist IC.

#### VETRIVEL MURUGAN

Joined Jul 23, 2021
12
 Parameters MineBea Motor 3X Motion HOLDING Torque 26.5 Ncm 40 Ncm Phase resistance 2.8 ohms 1.3 ohms Rated Voltage 2.8V 2.2V Rated Current 1.0 A 1.7A Inductance 5.4mH 2.2mH

I am using Minebea motor now. is it possible to replace this with new 3X motion motor? How to compare this & how to choose best motor?

#### Delta Prime

Joined Nov 15, 2019
1,149
hello there,welcome to AAC!

Stepper motor torque
torque-speed factor (kTω),
(kT is the torque constant and ω the speed)
kT ω(t) = Voltage to compensate the back
EMF.
The torque is directly proportional to the current.
The back EMF is the abbreviation of back Electromotive Force. It corresponds to the voltage sensed when the rotor is
moving in a changing magnetic field.
the factors which influence the current, thus the torque, are:
Inductance (LdI/dt, L = winding inductance).
The inductance prevents the current to establish rapidly in the phases.
Resistance (R = winding resistance).
The resistance influences the maximal current set in the phase.
The back EMF
When the speed ω increases, the back-EMF proportional to kTω increases and the current decreases, hence
the torque decreases. This explains why we observe on the torque/speed curves of the data sheet.
So, a Permanent Magnet (PM) stepper motor will provide high torque for you.
The rotor includes permanent magnets positioned in order to alternatively obtain South and North poles, which can interact with the varying magnetic field of the stator. Rotation is achieved by alternatively energizing the stator coils A-B-C-D and attracting the North (or South) pole of the rotor to the magnetized stator pole. When no current is applied, a small torque is required to
move the rotor from its equilibrium position due to the interaction between the permanent magnets and the stator. This is indifferently referred to as residual, detent or cogging torque or torque resistance.

#### Ian0

Joined Aug 7, 2020
3,238
I've used Minebea motors, and they are good. I don't know about 3X Motion.

#### VETRIVEL MURUGAN

Joined Jul 23, 2021
12
by comparing the parameters in the table
tell me which one is best?
comparing to minebea
according to the table for 3X motion torque is high it is good.
but the current is high
rated voltage, inductance & resistance is low
is it possible to replace the minebea motor?

#### Ian0

Joined Aug 7, 2020
3,238
They look reasonably similar. Are they the same frame size? And the same length? Do you trust the data? Are they well made?
The smaller the gap between the moving parts the more efficient they are - but also the more susceptible to poor manufacturing.
Is there anything odd in the torque-speed curves? Such as resonances?
Will your drive circuit cope with 70% more current?

#### VETRIVEL MURUGAN

Joined Jul 23, 2021
12
same frame size & same length
no curve data provided in data sheet
regarding current Driver circuit can. But my product battery backup will Affect if the motor takes more current

#### Ian0

Joined Aug 7, 2020
3,238
The current is higher but the voltage is lower. If you have a current-regulating drive then the power will be about the same.
They should be equivalent, but you will only know if you try one.

#### VETRIVEL MURUGAN

Joined Jul 23, 2021
12
The current is higher but the voltage is lower. If you have a current-regulating drive then the power will be about the same.
They should be equivalent, but you will only know if you try one.
Thank you for the support & clearing all queries.
Thank you for understanding

#### Irving

Joined Jan 30, 2016
2,072
The motor time constant L/R is important with stepper motors - a large L and small R means current takes time to establish but will be higher than a motor with smaller L and larger R, so slower motor (i.e cannot handle high step rates) but higher torque. The higher L can be overcome by increasing drive voltage but then requires active current limiting to prevent coil overheating so a more sophisticated driver is needed.

The 3X motor would potentially be able to step >10% faster than the Minebea, however at the same drive current it will be about 10% down on torque.

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,078
The thing to remember is the 12V 6-wire unipolar motor can be a 24V bipolar motor, not using 2-leads. 5-wire, I can't remember.

#### Ian0

Joined Aug 7, 2020
3,238
The thing to remember is the 12V 6-wire unipolar motor can be a 24V bipolar motor, not using 2-leads. 5-wire, I can't remember.
5-wire has its two centre-taps tied together - difficult to use it bipolar.
There are 8-wire ones as well, and you can make them into unipolar or two different specs of bipolar depending on whether you connect the in series or parallel.

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,078
ian. Thanks for that. I only played with steppers once. Rorze drivers. They were cool. They had s-curve profiles and all sorts of stuff. They even had embedded programming. I was trying to make LabView drivers for them for a monochometer and i lost everything.

I was playing with a totally different monochometer.

We ended up buying a monochometer. It had the required filters, but out old one was actually better optically.

It was wierd, I specified a system base on the money I had available and the technology. technology wasn;t ready, but the money was. Odd place to be, We had to upgrade because of the PDP-11 going away.

I wish I had 20/20 hindsight.

#### Ian0

Joined Aug 7, 2020
3,238
It was wierd, I specified a system base on the money I had available and the technology. technology wasn;t ready, but the money was. Odd place to be, We had to upgrade because of the PDP-11 going away.

I wish I had 20/20 hindsight.
I remember the Vax PDP-11, there was one at Marconi when I did my apprenticeship. It was in an air-conditioned room, and, as an apprentice, I probably wasn't allowed in. I do remember there being an advertisement for a Vax vacuum cleaners pinned to the wall!