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Stepper motor voltage vs performance
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Stepper motor voltage vs performance

by kadamr on Thu Aug 09, 2018 4:36 pm

Hi,

I have researched stepper motors and appreciate that the rated voltage isn't as important as the driving current or winding resistance. Still, there is one question to which I have never found an answer regarding stepper motor voltage.

I've read that if I run a low-voltage stepper motor (in the range rated 3-12V) above its rated voltage it becomes more efficient or it outputs more torque for the same current, so long as I'm using a stepper driver. However, for my application I only want to use AA batteries and can't provide a large voltage beyond say 5V (which is still above many 3-4V rated NEMA 17's).

Will the stepper driver step up the voltage such that so long as I'm within the stepper driver's input voltage range this doesn't matter as the stepper drive will step up to 30V or something?

Or must I use the stepper driver's maximum rated input voltage to get the best performance?

If I were to use the stepper driver's minimum input voltage will I really experience that much loss in performance?

I've read that using 40-80 V for a 3-12V stepper motor is ideal - there's no way I can achieve this with AA batteries. Should I be stepping up my battery voltage and is this even possible to that scale?

I'm assuming any chopping stepper driver will have similar features with regard to input/output voltage based on researching them - perhaps this is a poor assumption? I've never seen an output voltage quoted.

Please can you advice what the best approach is here? For reference - I'm making a panning motor for a heavy camera setup that must run reasonably quickly but also very, very slowly for time lapses.

Thanks in advance for any help!
kadamr
 
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Re: Stepper motor voltage vs performance

by adafruit_support_bill on Thu Aug 09, 2018 5:00 pm

I've read that if I run a low-voltage stepper motor (in the range rated 3-12V) above its rated voltage it becomes more efficient

Motor voltage ratings are best ignored - since they are not reported consistently from manufacturer to manufacturer. What you need to know is the current limit - and possibly the phase resistance.

Will the stepper driver step up the voltage such that so long as I'm within the stepper driver's input voltage range this doesn't matter as the stepper drive will step up to 30V or something?

No. Simple stepper drivers (such as the TB6612 drivers in the motor shield) do not boost or limit voltage or current. If using a simple driver, you need to know the phase resistance so that you can choose a supply voltage to keep the current within the limits of the driver and motor: https://learn.adafruit.com/all-about-st ... he-stepper

Some stepper drivers (such as the DRV833) have current limiting. This allows you to use a higher supply voltage - while keeping the current within safe limits. In these cases you need to choose a supply voltage that falls within the driver's rated range and configure the driver to 'chop' the current at a level within the motor's rated range.

The only real voltage limit for the motor is the voltage rating for the insulation on the windings. This is typically in the hundreds of volts or more.

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Re: Stepper motor voltage vs performance

by kadamr on Thu Aug 09, 2018 5:51 pm

Thanks for your fast reply.

There are two stepper motors I'm looking at - one is 12V, 350mA and the other is 3V, 1.7A and quotes significantly more torque. They are both similar prices and both NEMA 17, bipolar. Its not surprising that the second one has more torque due to its higher current rating, and therefore lower winding resistance.

I want to use 3-4 AA batteries so the 3V option seems all round better. Especially as it's a similar voltage to my microcontroller.

What am I missing? Is the second just a better option despite no price difference?

There are also very few options for low-voltage stepper motor drivers. Is the snag that I'm missing?
kadamr
 
Posts: 35
Joined: Wed Jul 03, 2013 6:29 pm

Re: Stepper motor voltage vs performance

by adafruit_support_bill on Fri Aug 10, 2018 6:07 am

the other is 3V, 1.7A and quotes significantly more torque.

The thing is, that motor was never intended to run at 3v. And the only way you will achieve anything close to the rated torque at 3v, is when the motor is not moving.

It is best to simply ignore the voltage rating. It is a mostly meaningless number. I run the "2.4v" rated steppers on my CNC with a 48V supply (and appropriately configured current-limiting drivers)
https://learn.adafruit.com/all-about-st ... e-law-4-10

I want to use 3-4 AA batteries so the 3V option seems all round better.

1.7A from AA cells might be achievable if you are using NiMH cells. But your run-time will be short.

The best way to start is by figuring out what torque you actually need for your project. Then work backwards from there to determine motor and power requirements.

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Re: Stepper motor voltage vs performance

by kadamr on Fri Aug 10, 2018 2:31 pm

Okay, thanks a lot, that's really helpful!

If I use a 12V battery supply (i.e. a 3s LiPo or 8 AAs) to run a stepper motor, how can I use that to power my microcontroller as well? I can't afford the space/weight for two battery supplies - plus it's not an elegant solution for the user (8 AAs for the motor and a separate 4 AAs for the microcontroller).

Could I use a 5V buck converter for the microcontroller? Will this cause any issues sharing the supply and can that be overcome easily?

Thanks!
kadamr
 
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Re: Stepper motor voltage vs performance

by adafruit_support_bill on Fri Aug 10, 2018 2:37 pm

The motors are going to be your largest current load. So choosing a primary supply voltage that matches your largest load requirements will minimize power losses due to voltage conversions.

The microcontroller will draw relatively little current - and buck converters are reasonably efficient, so a 5v buck converter to power the microcontroller is a good way to go.

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