For stepper drivers, what if the motor supply voltage is too low? - Page 1
Forum section: electronics / beginners

author: engineheat
author_rank: Frequent Contributor
timestamp: June 09, 2021, 09:36:10 pm
content: I ordered this driver for driving a bi-polar stepper motor:https://shop.watterott.com/SilentStepStick-TMC2100-5V-V2_1This is what the spec says:Motor voltage: 5.5...45VLogic voltage: 3.3...5VThe motor voltage goes to the VM pin in the image above. However, the spec mentions a voltage from 5.5V to 45V. I wonder if I can get away with 5V since I want to use a USB power bank that outputs 5V. The stepper itself can operate on as low as 3V.If not, can you recommend a simple, reliable boost converter? (I don't want something cheap that'll break soon)If yes, would it be possible to supply the same 5V to power the Arduino, the driver (VM and Logic voltage), and the motor itself (provided the motor draws less current than what the power bank can provide)?Thanks

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 09, 2021, 10:41:50 pm
content: Your power bank already has a stepup converter, as a Li-Ion battery typically has a voltage somewhere between 3V and 4.2V.A simple thing you can try is to just connect it and see what happens. These driver chips very likely have on-board charge pumps to generate enough gate voltage for the H-bridge Fets, and I can see a few possible outcomes:1. The chip just turns itself off when the input voltage is too low.2. The chip can not generate enough gate voltage and the motor won't work.3. The chip has marginal gate voltage and it will get hot quickly (Magic smoke, or thermal shutdown).Another thing you can try is to use another stepper motor driver. There are some 10+ variants in that same form factor.Another viable alternative is to just use two raw 18650 cells in series, especially if they have onboard protection circuits against deep-discharge.For an external Step-Up converter...There are literally hundreds of chips, and they usually all work. Just buy a few of the daily Aliexpress special.One of the boards I like is "XY-Lup". It has an USB connector for input, and output goes from less then a volt to 24V and it also has a display for voltage and current. It's probably not fit for you though, as output power only goes up to 3W.

author: rstofer
author_rank: Super Contributor
timestamp: June 10, 2021, 06:04:42 pm
content: You might gain some insight from "Jones on Steppers"http://homepage.divms.uiowa.edu/~jones/step/If your stepper motor will work in an acceptable manner on such a low voltage, go ahead and use the low voltage. It's done all the time on low torque/low acceleration applications.The thing is, motor windings are inductive and that limits the current rise time at each winding change. The motor can not run fast with much of a load simply due to inductance.So, voltage to the rescue! By applying many times rated voltage, the effect of inductance on winding current rise time is overcome. The only thing is, the driver needs to have current limiting to reduce the voltage after the rise time has been overcome.That's why the driver has a maximum voltage of 45V. It isn't to support 45V motors, it is to provide for over-voltage operation.You will note that the driver does indeed require an external current sense resistor to prevent overcurrent operation.https://www.trinamic.com/products/integrated-circuits/details/tmc2100/In short, you are taking the rounded leading edge out of the winding pulse.

author: rstofer
author_rank: Super Contributor
timestamp: June 10, 2021, 06:10:56 pm
content: If you read the Pololu "Overview" it talks about using a potentiometer to adjust the maximum current and using a higher motor voltage:https://www.pololu.com/product/1182The TMC2100 is supposed to be compatible with the Pololu deviceThis idea of using a higher motor voltage isn't necessarily good news for a small battery pack.

author: engineheat
author_rank: Frequent Contributor
timestamp: June 11, 2021, 08:51:54 pm
content: Okay, this is a really noob question, but here's the motor and the driver chip I got:The chip has M1A M2A M1B and M2B input.The stepper has brown, black, orange, and yellow wiring. Here's a schematic:According to this page:https://learn.watterott.com/silentstepstick/pinconfig/tmc2100/This is the connection:M1A Motor Coil 1M1B Motor Coil 1M2A Motor Coil 2M2B Motor Coil 2But it's still not obvious the right order of wiring since both black and brown corresponds to coil 1 in the motor schematic, so M1A and M1B can go to either black or brown and vice versa. And I guess the way I wire M2A and M2B will depend on how I wire M1A and M1B?Thanks

author: rstofer
author_rank: Super Contributor
timestamp: June 13, 2021, 02:30:24 pm
content: I can see where there is no definitive answer. Maybe just breadboard the 4 motor leads so you can swap things around.In the end, as long as you have the windings connected as a pair, the worst case is the motor has reverse rotation. Of course, 'reverse' has a pretty flexible meaning since the motor driver will be driven by a uC.https://electronics.stackexchange.com/questions/70643/how-to-reverse-rotation-direction-of-stepper-motorThere's a 'calculator' here that helps set up Vref for current limiting:https://learn.watterott.com/silentstepstick/faq/#how-to-set-the-stepper-motor-currentRemember the bit where I said you can use a much higher motor voltage as long as the current was constrained? Not that it helps for low voltage projects...