# Can i use 12v voltage regulator and a variable 0 to 30v dc power supply to control my 12v dc motor speed?

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I got a 12v dc motor with output power: 3.4 watts rated speed : 170 rpm rated current: 0.9A

Currently I has a variable voltage dc power supply which can varies the voltage from the dc power supply from 0 to 30v and a LM7812 voltage regulator.Can i slow down the motor speed by decreasing the voltage from the dc power supply because i still unsure what is the exactly speed is suitable for my motor to rotate in my final year project?

Beside that there is a lot of thing that confusing me and i need some justification. 1) Some people say if i use the 12v L7912cv voltage regulator in my circuit,the current that pass through the voltage regulator is not high enough to activate my dc motor.this is the link of the data sheet http://pdf1.alldatasheet.com/datasheet-pdf/view/88595/STMICROELECTRONICS/L7912CV.html.

2) Some people say if i use resistor to control my motor speed,the resistor will easily get burn up. 3) The goal of the dc motor is to rotate a rotating disc and the rotating disc is in direct contact with a flate surface so there is friction between them.So if in ideal case ,if i buy a 12v power supply and directly connect to the motor .Due to the friction and the load,the rated rotating speed will decrease and is suitable for my project.So in my circuit board do i need to buy any other stuff beside a 12v power supply?

I would like to say thanks first to anyone who reply me this question because i really need help to solve my fyp orject.Thanks a lot.

iceng3 years ago

Do you know how to measure motor current with a \$5 digital multimeter ?

mong73 years ago

@iceng thanks for your advise.I just found out it is a negative voltage regulator.Is there any difference to set up my circuit with negative voltage regulator and positive voltage regulator.

3 years ago

You should expect that a different polarity regulator will use a different circuit configuration, else there would be no advantage to the manufacturer of the dual regulators in fabricating different part numbers in a capitalistic society.

Early desk top computers were very dependent on a plus five, a plus twelve and a minus twelve power supply voltage because of the dynamic RAM ICs using different complimentary mirror circuits to provide the needed power.

iceng3 years ago

You need to take some measurements of actual current of your motor under actual load then decide if a 1Amp 7812 could run the motor.

BTW your pointer to a LM7912 is a negative -12 volt 1 amp regulator.

If your current requirement is greater there are ways to make higher current regulators.