Advice needed on power supply for stepper motor

Hi,
i want to control a stepper motor using a UNO and L298 shield. The stepper motor i intend to use has a 3V rated voltage and requires 2A / phase (see Attachment).

Being a newbie to this, i am wondering how to supply 3V - 2A to the stepper motor and 7-12V to power the UNO? Can anyone advise the best way to do this?

57BYGH420.PDF (50.6 KB)

Cheap and small stepper motors can be used with almost every stepper driver, but a 3A stepper motor is something else. A stepper motor should be used with a current in the first place. The voltage is not that important. So I think that the L298 might not be the best choice.

Can you search at Sparkfun.com for stepper driver ? The have a few different modern stepper driver boards.

An L298 is a poor choice for driving any stepper motor, and especially one that needs 3 amps. See the Thread stepper motor basics.

And note that a 3 amp motor is beyond the capacity of the "hobby" stepper motor drivers.

...R

Thx for your input guys.
i’m still a little undecided about this, as you both say the driver is unsuitable to drive a 3A stepper motor. Whereas, as far as i can see, the stepper i intend to use is a 2A motor. Assuming i am correct, then i think the driver card is capable of controlling the motor?

Shaarky:
the stepper i intend to use is a 2A motor. Assuming i am correct, then i think the driver card is capable of controlling the motor?

Sorry - I took the 3Amps from Reply #1 without checking.

For your 2 amp motor I would use a Pololu DRV8825 driver which can supply a little more than 2 amps. An A4988 would be right at its limit. You would probably need to add a heatsink to either board.

Of course you may find that in your project the motor would have sufficient torque without needing the full 2 amps - but you could probably only figure that out by experiment - adjusting the current limit on the driver board.

...R

When using a chopping driver you do not need a supply that delivers the full motor current since the energy will be converted in the motor windings.

not sure why everyone plain ignored your request and told you to use anything else.

as you can see people do not really care about applications, only their favorite way of doing things.

I am surprized that people do not say to use a teensy and never to use an UNO because the Teensy is faster and has a better ADC.

the first thing is the APPLICATION. what do you want to do. if you want to move a NON-CONTACT motor, that just located a thing, then the L298 is a PROPER driver and a good choice.

as comparison an L298 is a LM317 power supply, the chopper driver is an switched LM2596
I would wager that every person who says to use something else will use an LM317 on their own project.

the question is what are you trying to do ?

it appears that every answer is "I do not care what you are doing, use the parts I like" and for that I appologise for all those who are not well versed in engineering and steppers.

what you will see next is a slew of people telling you to use some extreemly high voltages like 12 volts or even higher, again without a clue to your application.

// rant mode off

the L298 will have a voltage loss through the driver itself. like any power supply, you can not feed it the same voltage as you want to get out of it.

second, without knowing your application, any discussion of power needed is just a disservice and poor engineering.

stepper motors like LED's have data sheet parameters. you can drive an LED with 50mA if you know what you are doing, even though the data sheet wants you to limit to 10 or 20.

Just because you can driver the stepper at 2 amps, do you need to ?
just because you can drive a stepper at 35 volts, do you need to ?

I would offer that it would be better to disregard all the bad advise so far and post your application. Then an intelligent discussion can occur as to the PROPER driver to use.

Shaarky:
Thx for your input guys.
i'm still a little undecided about this, as you both say the driver is unsuitable to drive a 3A stepper motor. Whereas, as far as i can see, the stepper i intend to use is a 2A motor. Assuming i am correct, then i think the driver card is capable of controlling the motor?

The L298 is a PROPER stepper driver and can handle the power you listed.

Please wait for the engineering and discussion about your application before throwing away perfectly good parts.

dave-in-nj:
The L298 is a PROPER stepper driver and can handle the power you listed.

Dave, I very much respect your entitlement to disagree with my approach.

If I edit my stepper motor basics Thread to refer to the A4988 and its ilk as “speciailized” stepper drivers will that adequately distinguish them from L298s and dispense with the need for these comments.

Also, it would be a great service to newcomers if you could write a Thread to explain how to use an L298 as a stepper driver. Then they could read your Thread and my Thread and make up their minds. I would be very happy to help with the writing - but the content must be yours.

…R

Robin2:
Dave, I very much respect your entitlement to disagree with my approach.

If I edit my stepper motor basics Thread to refer to the A4988 and its ilk as "speciailized" stepper drivers will that adequately distinguish them from L298s and dispense with the need for these comments.

Also, it would be a great service to newcomers if you could write a Thread to explain how to use an L298 as a stepper driver. Then they could read your Thread and my Thread and make up their minds. I would be very happy to help with the writing - but the content must be yours.

...R

Robin,

I highly respect your posts and think that your attempt at an introduction is a very valuable contribution and is very needed.

I am in the process of writhing the introduction to steppers and elaborating on the details that I see are often skipped in many of the replies in this forum. I believe that it would compliment yours.

If you were around in the days of the BasicStamp, no one used a pre-made driver, but the huge following used motor nameplate voltage and home-made H-bridges. the enormous amount of talent and huge diversity of devices that were made and powered and operated shows that one does not need to jump into specialty circuits and drivers in order to make a motor move.

I get a bit flustered when a newbie says "here is what I have and this is what I want to use", and then he is totally ignored and told to throw away what he has and to buy new parts. Especially when the application might call for exactly what he has. And doubly flustered when the application is not known by people giving the advise.

dave-in-nj:
I am in the process of writhing

I hope it is not that hard. :slight_smile:

And I look forward to it.

...R

dave-in-nj:
what you will see next is a slew of people telling you to use some extreemly high voltages like 12 volts or even higher, again without a clue to your application.

Actually we don't need to. The OP has chosen that motor for some reason (which we also do not know) But a motors task is to produce torque by converting electrical energy to mechanical. The holding torque of the motor is 0.9Nm so the required torque must be below that. The OP does not state at which speed he need the torque. So all advice given here is of general nature. And if you should make some general statements oabout stepper motors they are:

  • Use a current controlling driver. Driving a stepper with constant voltage is asking for trouble. The driver can be chopping (most are) or linear. And since most chopping drivers provide microstepping use that as well
  • The higher the supply voltage the better the performance. There is a upper limit for that though at about 32sqrt(L) where L is motor inductance in mH. For this application the upper limit is 50V. The lowest voltage at which a stepper should be driven is 4Vmot in this case 12V. Below that voltage the motor will not perform satisfactory with a constant current driver.

When connected to a chopping driver the current demand on the supply will be about 0.7A

the stepper motor is designed first by the number of turns of the winding.
the winding resistance and amps are used to calculate the voltage.

the motor voltage is the result of a calculation of the MAXIMUM current for the motor based on the physical construction.

the nameplate voltage is the voltage than can be used on said motor at a constant state to deliver the maximum current. the minimum current is that needed to move the motor from one detent to the next. any value in between should be selected by the application. and I am all for doubling that CALCULATED value.

the OP has not offered the actual application so we do not know that it is not for something like a speedo or tach needle and the only power requirement is to move the shaft of the motor. an application that does not require maximum current.

It seems that the application is ignored and if the OP chose a motor that offered 10 times the power, the suggestions would be the same, to drive it as hard as you can to get 'better' performance. how many orders of magnitude over the required power is needed ?

What is being proposed is that the motor is unconditionally required to reach it's maximum torque, in the shortest time possible, regardless of the actual application.

what is not being considered is that as power increases proportionally with the voltage, the iron losses increase as the square. I have seen posts on this forum that people have recommended to start at 24 volts, and then add a fan to help remove the heat because the motor will get hot. and totally ignore that in that case the motor was moving a magnet, in a non-contact application at speeds of 10cm per second. (just above the speed of paint drying)

what is not considered is that the higher the voltage, the more 'snap' the motor will have and even to the point of making audible noise.

my point is that if you require that motor move a distance in 1 second and it can move that in 1/10 of a second, what engineering reason can anyone give to require that it to be done in 1/1000th of a second ?

ie: the application should come before the details of voltage selection and before the selection of a driver for the motor.

Robin2:
I hope it is not that hard. :slight_smile:

And I look forward to it.

...R

thanks for pointing out my spelling..... windoz recently blessed me with an update that now has a firewall preventing my aircard from connecting to my network. I am booting to Ubuntu and the spell check turns itself on and off at will, often after I correct one word.

I fear that my normal bad spelling and frequent spelling mistakes will be multiplied without the help of intelligent software.

I think this debate may be over the OP's head. If he knew
(and understood ) what any of you are saying he obviously would not have posted. You need to explain to the OP why the L298 andthe Pololu A4988 are APPLES & ORANGES. One is a golf cart and the other is a race car.

You have all made a good start...

@OP ,

You might want to read this.

Wow i wasn't expecting to find all this. Sorry guys i have been busy elsewhere, and just got round to revisiting this.
In summary, i think its fair to say i should have explained a little more about the first project my son and i decided to do after i gave him a starter kit for Xmas.

Our project is to automate the roller blind in his bedroom. We have a number of ideas on how we can control it, but neither of us are clued up on motor drives. I measured a force of approximately 1 KG currently needs to be applied to manually move the blind, using the 50mm dia pulley wheels and cord. Doing some maths, and allowing a generous bit on top, it appeared i needed a fairly biggish stepper motor to achieve the required holding torque. i found a motor, and then looked at the driver needed. The L298 board seemed to capable of outputing the 2A / phase needed, but my concern was the 3V rating on the motor. The ardino UNO board works on a higher voltage supply, and i assume that we need to step the motor supply voltage down?

I hope this throws a little more light on what we are trying to do. We have not yet purchased any components, and are open to any advice as to the best way to proceed.

Shaarky:
but my concern was the 3V rating on the motor. The ardino UNO board works on a higher voltage supply, and i assume that we need to step the motor supply voltage down?

One of the reasons I wrote stepper motor basics was to throw some light on the question of stepper motor voltage - did you read it? If there are things you don't understand please let me know.

Regardless of what sort of driver you decide to use, the Uno voltage has nothing to do with the motor voltage because the motor needs its own separate power supply.

...R

Hi Robin,

I have read though your guide, and it did lead me to believe that the board and motor needed separate power supplies.

what I'm trying to figure out is how best to provide those supplies preferably by using a single power source with enough voltage for the boards and amps for the motor, but somehow stepping the voltage down to supply the motor...maybe using a potentiometer? How would you approach this? can I use a single power source, or does it have to be 2 separate power supplies?

Since you will need a supply for the motor, it will probably be a higher voltage supply (9V to 12V if you use
a chopper driver) so you could add an LM2596 buck switching supply to step down the voltage to 7V for the
UNO Vin ext. dc power barreljack). They are cheap on ebay.