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How should I choose a power supply for a stepper motor, if the motor requires 7V and 1A? Should I buy a power supply of exactly 7V and current of minimum 1A?

Daniel
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aneesh cool
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    Step back a bit. Do you know how to *control* a stepper motor? – Eugene Sh. Feb 23 '18 at 18:51
  • Through stepper driver – aneesh cool Feb 23 '18 at 18:52
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    Cool. And this driver, do you have it's specifications? You don't connect the motor to the power supply, you connect the driver. – Eugene Sh. Feb 23 '18 at 18:52
  • Iam using sg90 servo motor .I was generally asking how to choose a power supply.I give power from a battery into bread board.servo is connected to arduino – aneesh cool Feb 23 '18 at 18:54
  • Rated current is usually quoted at max per coil. Since you normally drive a stepper with two coils active some of the time, you need to double the current. You can use 7V if you want, but as @EugeneSh. mentions, you will lose a little volts across the driver. – Trevor_G Feb 23 '18 at 18:58
  • @Trevor_G But the voltage should not exceed 7 volt ryt??.So if the rated current is 1A should I buy 2A supply??.Iam sry iam jus started learning electronics – aneesh cool Feb 23 '18 at 19:01
  • Not necessarily, if the driver is a current control driver, the volts can be a bit more. Just make sure the driver can handle the difference. You need a bit of margin on the amps too. If you get a 2A supply and try to draw 2A the supply might limit on you depending on tolerances, plus the supply will be running at it's max and run hot. A 3A or 4A would be more reliable. – Trevor_G Feb 23 '18 at 19:04
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    The driver might be smart enough to take a very different voltage and convert it to whatever is needed. – Eugene Sh. Feb 23 '18 at 19:05
  • I got 4 sg90 servo voltages 1.5V each and i dont know the currennt rating.How can I give power supply to this servo now.Iam connecting my servo to arduino and for PS bread board – aneesh cool Feb 23 '18 at 19:13
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    The SG90 is not a stepper motor. It is a servo motor for remote control vehicles. As such, you don't need a driver as you would with a stepper motor. You can drive it from software using an Arduino. Power to the servo, ground and control signal wire to the Arduino, add a dash of software and you have a computer controlled servo. – JRE Feb 23 '18 at 19:21
  • @JRE Iam running 4 servos which needs 7 volts.How to give them power supply.I used a battery of 7 Volt and current of 0.1A but the servo did not run.I connected the battery terminal to bread board and connected the servo to the bread board.but its not working – aneesh cool Feb 23 '18 at 19:24

1 Answers1

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The SG90 is an RC servo, and can easily be controlled by an Arduino using the servo library.

The SG90 is intended (like most servos) to be operated from battery voltage around 5V. They usually work just fine on anything from 4.5V to 6V.

I doubt that an SG90 will really draw 1A. I am currently running a couple of much heavier servos (30kg as opposed to the 1.5kg of the SG90) on a single 5V supply rated for 2A. I am operating the servos at the upper limit of their load rating, and the 2A power supply is good enough.

A 5V powersupply rated for 2A would be more than enough to handle your little SG90s.

A single 5V , 1A supply would probably handle all four of them at the same time just as well.

I in fact ran a couple of 10 kg sevos from a 5V, 1A supply for a while. That did tend to over heat and shut down, though.

I see in a comment that you connected it to a battery and it didn't run.

That is correct. A servo will not run when only connected to power. It MUST have a valid control signal as well. You can generate that control signal with your Arduino. Refer to the Arduino reference page I linked above. It includes some tips on connecting your servos to an Arduino, as well as a couple of examples. (The examples include code, a schematic diagram, and a wiring duagram.)

These servos will not rotate like a regular motor. They are intended to position the shaft in response to the control signal. They rotate only 180 degrees, and with the correct signal you can set the shaft to any position in that range.

Servo ratings are weird. In the datasheets they are rated in newton centimeters of torque, sometimes in inch pounds. Then they advertise them in kilograms. A 1.8 newton centimeter servo is advertised as a 1.5kg servo. The conversion from newtons to kilograms is OK, but the centimeter is ignored - even though that is the thing that makes the difference between a force and a torque.

JRE
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  • Thank you very much.But generally should we choose a power supply of exact voltage rating and little more than current rating?? – aneesh cool Feb 23 '18 at 19:40
  • See the question referred to in the comnents. In general, yes. Voltage exact, current can be more. – JRE Feb 23 '18 at 19:45
  • I read that and iam confirming it as iam not from electronics background and thanks for your explanations – aneesh cool Feb 23 '18 at 19:46