Can I use USB-only power to run a stepper motor?

Hey all,

I’ve got an Arduino Uno Rev 3 and an Adafruit Motor Shield v2.3 on top of it. My design requires sending input to the Arduino (numbers). Therefore, I need to have the USB cable always connected to the Arduino. I’ve got also a stepper motor (8V @ 0.4A) which is connected to the Adafruit Motor Shield (M1 & M2).

Is this generally okay for the USB port and the Arduino/Shield to run only USB power?

Your motor needs a motor supply.

That may come from the USB Port (5V @ 0.5A)?

Convert the ratings to Watt to compare them.

Even if it were arithmetically possible,
it's a bad idea to share the supply with fast switched inductive loads.

The Adafruit shield is there to prevent inductive kickback, as far as I know.

Do Adafruit provide a warrenty that covers possible harm to expensive PCs or Laptops ?

Kickback is a different problem, and I would also trust Adafruit in that respect.

Do yourself a favor, and get a separate power supply for the steppers.
Even if they are rated for 8V, most steppers are driven with higher voltage and current controlled.

Thanks for that constructive response. Are there any recommendation for mobile solutions? Battery?

Please tell us what the stepper motor is to do. Steppers are not very efficient and may not be the best choice for battery operation.

On page 52: https://cdn-learn.adafruit.com/downloads/pdf/adafruit-motor-shield-v2-for-arduino.pdf

It says:

You can't run motors off of a 9V battery so don't waste your time/batteries!
Use a big Lead Acid or NiMH battery pack. Its also very much suggested that you set up two power supplies (split supply) one for the Arduino and one for the motors...

Are they talking about this: Akku Racing-Pack für Carson mit Tamiya Stecker - 9,6V / 2200 mAh NI-MH Akku/Hochleistungs RC Pack Akkupack: Amazon.de: Spielzeug ?

The stepper needs to rotate a very light-weight piece of plastic.

that actually looks promising:

Yet this would contradict:

You can't run motors off of a 9V battery so don't waste your time/batteries!

Not getting it ...

Motors need the correct voltage to run. They also need the correct current. A 9V smoke alarm battery has the voltage but not the current capability.

Like I said, stepper motors are very inefficient and not suited to battery power.

That tells me a little bit, but not the whole story. Why a stepper?

In that thread you see a video of the setup from a solved problem: Stop stepper motor when IR beam breaks, reliable and independent (no additional power source; only USB power)

Sorry for spamming links: Since I am nearby a (mboile) laptop; would that be enough: USB to 2.1mm Male Barrel Jack Cable [22AWG & 1 meter] : ID 2697 : $2.75 : Adafruit Industries, Unique & fun DIY electronics and kits

So that would basically mean I got the power of two USB ports... ending up to provide 10V @ 1A?

The 9V thing is about the little rectangular batteries that were used for smoke alarms. They can't provide enough current to drive a motor for long, if at all, but people keep making that same old mistake because they bought a kit with one of those worthless batteries in it.

That's not to say that you couldn't drive a motor off a more substantial 9V battery.

The Arduino UNO has a 500 mA 'polyfuse' to keep it from drawing more than 500 mA from the USB cable.

8 Volts at .4 Amps is 3.2 Watts.
3.2 Watts at 5 Volts is 0.64 Amps (640 mA).

Even if you had a 100% efficiency DC to DC converter to get the voltage up to 8V you could not draw enough current from the USB cable to feed the stepper.

I would try a 2-cell 18650 Lithium Cell holder. That will give you a nominal voltage of 7.4V which will likely be adequate for your stepper AND your Arduino. Figuring 45 mA for the Arduino and 400 for the stepper you might get about four hours per charge.

Thanks for the detailed answer; I am wondering why I can run my setup (Arduino + Shield + stepper motor + ir beam breaker (soldered to 5V pin) for hours, with just USB power and no external source ... Why is all that working with no external power source?

Perhaps someone lied to you about the power requirement of your stepper.

No, the stepper specs are printed on it, and it is exactly that model: NEMA 14 Motor - Joy-IT

It is just weird to me that all this works without external power ...