Build a voltage step down circuit for stepper motor

[georgio17]

I want to build a step down voltage circuit for my stepper motor.
The supply is a 12V DC battery
The rating of motor is 3.2V and 2.8A
How am i supposed to step down the voltage to 3.2 and for that particular current level.
What components are required?
A circuit diagram would be well apprciated..

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I would like to manually build one but can the micro stepping units also in the above site be used (This is in case i can't build the circuit)
Thanks!!

 

[chuckey]

Just use a (12-3.2)/2.8 ~3 ohm resistor at 30W per phase. Proper stepper drivers use a constant current output via PWM. This will help in keeping the stepper's speed up.
Frank

 

[Krishna Patil]

Easy way to do that would be L298 driver IC with a heat sink. I think you can supply 12V to drive motor but accordingly place sense resistor to limit the current. Since voltage is 3.2 V and current is 2.8A. If you use 12V then maximum current is 0.75A

If you use a sensing resistor greater than 2.678 ohm ( use nearest value possible ) , this would make 2V(V sens) when around 0.75A current is flown through load and current is limited and motor will be safe.

 

[georgio17]

Thanks for your help.
i didn't understand.. do you mean that i should connect a 3 ohm 30w resistor at each of the 4 outputs of the motor driver or one of it at the input of the motor driver.
Or did you mean something else cause i am a beginner in such projects so i get confused.
Thanks.

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And also i have another problem.
I am using a 12V car battery so i require 3.3V and 3A current to power the motor and i also require the 5V to run the micro-controller. Any idea how to do it using just a single source?

 

[Krishna Patil]

If you are confused about connecting motor driver, then here is explanation
Look at the datasheet of L298. Place a 3ohm, 5W resistor in between pins 1 and 15. output pins connect to motor. Input pins to microcontroller. Enable pin to PWM of microcontroller, if you want to control speed or else place it logic high.

Vs - Supply Voltage from your battery ( 12V ) . Stepper motor can take voltages more than rated voltage. but current should within limit. So for 3.2V max current is 2.8 A . If calculate for 12V then it is 0.75A.

Vss- Logic supply voltage ( +5V)

If you run microcontroller on +5V , it would draw few milliamps. It is well within limit of 7805 regulator which is 1A. Use that regulator. So that you could run on single power supply.

 

[D.A.(Tony)Stewart]

If you are a newbie to using bridges and steppers you might want to master understanding of how it works before you attempt to design it. Understand the trade-off with torque, speed , current limit, heat loss, noise, vibration. also complexity, smoothness of of micro-stepping vs torque & speed.


Get the kit https://www.robokits.co.in/downloads/RMCS1104_MicroStepperDriver.pdf

 

[georgio17]

Thanks for your help..
I have built the circuit as sown in the diagram
Without connecting the motor i am getting the output after the pics at 5v which is correct and also i am getting output after the driver at 12v but its fluctuating.
But when i connect the motor, the motor does not turn at all..
I have found out the sequence of the motor and connected as per that but still motor does not turn..
When i just touch the motor to the battery directly 1 wire at a time it moves but it does not rotates while in the circuit.
Please help..
Thanks..

 

[chuckey]

I do not understand why you have taken the Isense inputs to +5V, they seem to be earthed in other circuits*. Have you got the phases of the motor correct?, try swopping over the wires to any one motor coil.
Frank
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[georgio17]

Sorry...
This is just reference..
I actually connected a 3.3ohm 5w fusible resistor across pin 1 and 15 as said by Krishna Patil

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otherwise can you tell me what motor driver specs to search for on ebay.
Can this be used??
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OR

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OR
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Cause i am in an urgency now and if my circuit does not work i need to buy one as backup..
Thanks again for your help..

 

[D.A.(Tony)Stewart]

If you want to build a DC-DC converter, you want to know the Stall current or winding resistance.

Here is one chip that works https://www.ti.com/lit/ds/symlink/tps54428.pdf

 

[georgio17]

Anyways i decided to buy a motor driver but i wanted to know which one cause i have the follwing problems..
My stepper motor NEMA23 19kgcm torque
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I want to know if this one is ok
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because
i want to program the motor to run in steps after a while so how do i go about connecting it to the driver?? I mean that the output of the MC goes to which ports of the above driver so that it rotes the way i programmed??
Another thing is that i may have to continuosly supply current to prevent the motor from moving because of the weight..Due to this a high current is required to drive the motor.. I am hoping will this be be able to bear the heat generated??
Thanks for all your help

 

[D.A.(Tony)Stewart]

It is best to consult with supplier giving load specs, in torque, friction and inertia and ask for supply requirements, but controller seems to have suitable options. Understand any current derating in spec for continuous use in full winding mode. Dont use an undersized motor.