DC motor voltage control

[ivan3k]

I want to build a circuit to control the rotation speed of a slot car motor. The motor (0-10V/2A) will be supplied by a 0-30V/3A DC power supply.

The rotation speed will be controlled by the analog output (0-10V/5mA) of a National Instruments data acquisition board.

To sum up, I need a circuit to vary the voltage of the motor based on the change of daq AO voltage.

Any ideas would be awesome.

 

[audioguru]

Usually, Pulse-Width-Modulation, not simple voltage, is used to control the speed of a DC motor. Then the speed does not change much when the load changes.

Your power supply voltage is 3 times too high but additional circuitry can reduce its impact.

 

[ivan3k]

I would prefer to use voltage to control the motor speed because the LabView interface of the analog output is easy to implement. I must use the daq board since the motor is part of a bigger experimental setup. The setup includes other sensors; the data acquisition and the motor control have to be made simultaneously.

The load of the motor will be constant.

Regarding the power supply, the voltage can be varied to meet the maximum voltage of the motor.

 

[crutschow]

Here's a simple voltage-controlled PWM circuit using a 555 oscillator and a comparator. You can put the control voltage at the comparator input instead the pot.

 

[ivan3k]

Thanks for the replies, audioguru and crutschow.

Here's a simple voltage-controlled PWM circuit using a 555 oscillator and a comparator. You can put the control voltage at the comparator input instead the pot.

As I'm not used to some components, I have a doubt about how to connect my control voltage in the comparator instead of the potentiometer. Also, do you find that it is necessary to isolate the daq control circuit from the circuit that powers the motor? If so, how do I do this isolation? By an opto-isolator?

I found this **broken link removed** that pretty much does what I need, but again, is it possible to use my control voltage?

 

[ivan3k]

Thanks for the replies.

I modified the proposed circuit to suit my needs. The modified circuit is below.

I still have a doubt. Do I need to connect the negative from the control voltage in the ground of the circuit?

 

[audioguru]

I still have a doubt. Do I need to connect the negative from the control voltage in the ground of the circuit?

If you do not connect the negative from the control voltage to ground then the (+) input of the comparator will not have any control voltage and will not work.

 

[ivan3k]

Do you think that is wise to isolate both circuits by an opto-isolator?

 

[crutschow]

Do you think that is wise to isolate both circuits by an opto-isolator?

Don't see any particular need for isolation unless there's some reason you need to keep separate grounds.

 

[ivan3k]

My concern is about the different current levels, as the control circuit has 5 mA and the motor draws about 2A from the power source.

 

[audioguru]

My car's starter motor draws a few hundred Amps and its clock draws less than 1mA and they have exactly the same ground.

My city draws hundreds of thousands of Amps and my house draws a few hundred Amps and they have exactly the same ground.