I have ordered a Nema17 (17HS4401) stepper motor from AliExpress to work with an Adafruit TMC2209 stepper driver. My stepper will be powered with 15V 3A from a USB-C PD module and that 15V 3A supply will also be passed through the step-down converter to step down to 5V 3A to power the ESP32 and TMC2209. I have read that the stepper can create regenerative current which will push back through the supply and damage components like my step-down converter. I can apparently use a brake resistor or a capacitor, but I don’t exactly know how to do it or what exactly to use. I wish to order the parts from Core Electronics, I already have a cart full of the components I am planning to use, but now I am on my final stage of going over it all and adding protection to prevent damage.
Parts in the circuit:
• Adafruit USB Type C Power Delivery (HUSB238)
• DC-DC Adjustable Step-down Module 5A 75W
• 17HS4401 Stepper (from AliExpress)
• Adafruit TMC2209 Stepper Driver
• FireBeetle 2 ESP32 C6 IoT Development Board
I think you might be referring to a PWM controlled brushed DC motor here. The voltage generated by the collapsing field here is the culprit. Cured by fitting a “Flywheel” diode. This appears across the motor windings and does not “push back” into the supply. I am not going to go into details here. Research is the key.
A low value “Braking” resistor can be used to assist motor stopping (regenerative braking) when the motor has to be stopped but that is a separate thing. A stepper does not need this. It will just stop and hold position where without braking a brushed motor will run on due to mechanical inertia.
I think that a purpose designed stepper drive board will take care of these worries for you.
Cheers Bob
Add a large electrolytic capacitor across VMOT (or across the input of your DC-DC converter).
It absorbs spikes, smoothing voltage backflow.
Typical values: 470 µF – 2200 µF, 25V rated or higher for a 15V system.
Works best in combination with a small brake resistor if you anticipate strong deceleration.
Hi Lost, Ahsrab
One other problem which is more apparent in PWM controlled brushed motors is connecting wire inductance when switching larger currents. This causes a “charge pump” effect and adds a voltage to the supply thus increasing the apparent voltage. This can be minimised by reducing this inductance. Have the supply wire length as short as possible and don’t coil up. Use a wire as large as practicable. Try NOT to use very small hook up wire.
This will minimise the effect. Fit this cap as close to the switching point as possible like the VMOT input to the driver. This will be more effective than across the 5V regulator.
I think in this instance a LM7805 linear regulator might be the better choice here as it will reliably get rid of any interfering beasties you happen to produce. Provided you have enough current capability available as being linear the current you get out will be the current you have to put in. These are good for up to about 800mA to 1A output.
Ashram. A brake resistor connects across a motor winding as is usually switched. As a stepper has many windings which one are you going to connect to and how are you going to switch it. It is not economical to leave such a resistor in place continuously as to be effective it has to be a similar value to the winding resistance and so will consume the equivalent to the stall current continuously. Not very efficient.
The is usually to prevent over run with a brushed motor. I may be wrong but I don’t think a stepper is affected by this or its positioning accuracy would be lost.
Cheers Bob
The stepper I am using will accelerate within 1 second to a peak RPM of around 150 to then decelerate to a stop. I plan to have it run at the set peak for 6 seconds with 1 second to accelerate and 1 second to decelerate to a stop, making for a total of 8 seconds. It will be pulling 1.4kg of force (0.21nm) against gravity. I am not entirely sure what the deceleration will cause as I don’t know a whole lot about electrical circuits or electronics in general. I have read that the stepper can/will push voltage back into the supply during deceleration, so I want to make absolute sure that it won’t fry my DC-DC converter as well as anything else connected to the DC-DC converter.
Would a “1000uF 35VDC Low ESR Electrolytic Capacitor” be enough for this, or would I require other protections?
The deceleration won’t be too bad for Nema17. Brake resistors are usually for big motors with a lot of kinetic energy. If you want to absolutely ensure that your Buck Converter won’t be fried, that capacitor should be more than enough for a 15V motor.
