Stepper motors are commonly used in automation and control applications where precise positioning and motion are required, such as in 3D printers, CNC machines, and robotics.
When using a stepper motor in a battery-powered application, special considerations must be made to select the appropriate battery voltage and current capabilities. The battery must be able to deliver adequate power continuously to drive the windings of the stepper motor.
This article provides a step-by-step guide to powering a stepper motor using a battery.
Power Requirement of a Stepper Motor
When selecting a power supply for a stepper motor, it is important to calculate the required voltage, current, and overall power capability. Key factors include:
- Motor-rated current – specified in the datasheet, required current per phase Driving voltage depending on motor size:
|Motor Size||Driving Voltage||Supply Current/Phase|
|Nema 8 – Nema 17||12 – 24VDC||1 – 1.5A|
|Nema 23 – Nema 24||24 – 48VDC||2.8 – 4A|
|Nema 34||48 – 100VDC/30 – 70VAC||6|
|Nema 42 – Nema 52||110 – 220AC||6 – 8.5A|
Power formula –
P = nIV*1.2
3-axis motion control system using 3 NEMA 17 stepper motors, each with a rated current of 1.5A. To power the motors from a 24V battery pack.
n = number of motors (3)
I = rated current per motor (1.5A)
V = driving voltage (24V)
margin factor = 1.2
Plugging this into the formula:
P = 31.5A24V*1.2= 129.6W
So, For the 3 NEMA 17 stepper motors, the estimated power is around 130W.
Steps by Step Process
The following will provide a step-by-step guide on powering a stepper motor from a battery power source:
Step 1: Selecting the Battery
The battery must be capable of supplying the current required by the stepper motor on a continuous basis. The motor’s rated current will be provided in its specifications.
Step 2: Adding a Motor Driver
A motor driver bridges the battery’s higher voltage to levels suitable for motor coils, efficiently controlling stepping motion. Common choices are MOSFET-based or dedicated ICs such as Allegro A4988, which are well-matched to manage higher motor currents.
Step 3: Choose the Stepper Motor
Select a stepper motor that matches the motor’s torque, speed, step angle, and voltage requirements.
If necessary, motors can be custom-wound for lower voltages; specify the desired coil current. Leave a 50-70% safety margin on the current rating to accommodate losses.
Step 4: Add Current Control
Implement current control for safe motor-to-battery interfacing. Use a stepper motor driver IC, such as the ULN2003, to drive the coils.
Step 5: Connect the Battery
Wire the battery pack’s positive and negative terminals to the motor driver board. If necessary, add a switch to the connection for convenient power control.
Step 6: Apply Control Signals
Generate coordinated step and direction signals using a microcontroller. Connect these digital signals to the stepper driver IC. Sequence the signals precisely to achieve the desired motor rotation and positioning.
Step 7: Add Protection Diodes
Install diodes across each motor coil to provide a path for inductive spikes during coil switching. This prevents damage to the driver. Fast-switching diodes like 1N4001 are suitable for this purpose.
Step 8: Smoothing Power Fluctuations
Fluctuations in the battery output can cause issues with stepper motor performance. Adding a 1000uF 25V electrolytic capacitor across the motor power connections can help filter any voltage ripple or spikes.
Step 9: Select Proper Wiring
Use thick enough wires to handle the stepper motor’s current draw without excessive voltage drops. Refer to a wire gauge chart and the motor specs.
Step 10: Add an On /Off Switch
Install an on/off switch to disconnect power from the battery when the motor is not in use, preserving battery life.
Frequently Asked Questions (FAQs)
1. What Happens if the Battery Voltage Is Too Low for the Motor?
Answer: Too low voltage will reduce torque and speed, potentially stalling the motor. Custom winding or gearing may help.
2. Can Multiple Batteries Be Combined to Power a Motor?
Answer: Yes, batteries can be combined in series and parallel arrangements to provide suitable voltage and current.
3. What Happens if the Battery Voltage Is Too High for the Motor?
Answer: Supplying excessive voltage to a stepper motor can cause overheating, potentially damaging the motor and its driver. It can also increase torque and speed, potentially exceeding safe operational limits.
Powering a stepper motor from a battery requires careful selection of components and proper current control. Combining a suitable battery, stepper motor, driver IC, and microcontroller allows precise position control using a portable power source. Proper wiring and current management are key to success.