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Driving a DC motor from the output of an Op-Amp

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Arjames090686

New Member
Hi All,

I need to build a circuit that would drive a motor based on the error value of an Op-Amp.

I would need to set a reference voltage of lets say 230v (using a potentiometer??). The actual voltage would be the output from a variac (lets say 220v. I would then need the output from the Op-amp circuit to drive a motor (assuming dc) that is connected to the adjustment dial on the variac either clockwise or anticlockwise in order to adjust the output voltage from that device.

Any suggestions on how to do this for an amateur!!
 

Chippie

Member
Sounds dangerous for me using such high voltages........

Start with something a bit lo level and work from there.....

look at how a servo works..
 
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Arjames090686

New Member
it ok. i am working supervised in my place of work by design engineer! :)

i am doing an ONC in electrical/electronic engineering and this is for my project. work gave me the project so now its mainly research and trying to build whilst supervised.
 

tcmtech

Banned
Most Helpful Member
I asume your trying to make aself adjusting constant voltage source device of sorts.

A set of reference voltage sources with two op amps could possibly give you a high/lo set of reference points and resulting dead band between them. If one triggers the motor through a relay that tells it to turn up the variac output until it reaches its preset dead band and the other is set up to tell it turn it down if it goes past it preset point you could feasibly have a self maintaining voltage source with a rather slow response time.

Ideally if you needed a stable AC voltage source a constant voltage transformer would be far more accurate and have much better response times in the area of less than a full cycle of the alternating current source.
 

Boncuk

New Member
Hi,

use a low voltage output transformer (6 to 24VAC) connected to the output of the variac. Rectify that voltage and feed it into a window comparator. Use a very stable reference voltage.

Use the outputs of the window comparator with a narrow window to control the motor pot for the variac.

Boncuk
 

Arjames090686

New Member
thanks all.

i suggested using transformers to the supervisor in work and he asked me to try doing it by building a circuit etc. as it is a college project he wants me to learn a lot more by doing it that way.

i found some Forest M Mimms books and one was on Op Amps, the window comparator was in there and i noted down alll the details. I liked the idea of having the deadbands and i assumed this would be the way of doing this.

sat down yesterday with my colleague in work and he helped me select a 'type' of motor that i may decide to use. It was either a Bi-directional AC motor or a geared dc motor. I now have to find out how to drive it from the output of the comparator circuit.

It's a struggle and a lot of information to take in but all good fun!!!
 

mbarazeen

Member
you can find a similar one in a fully automatic AC voltage regulator that is comercially available. it is with a DC motor to adjust the tapping pointer of the toroidal coil of the regulator.
try to get one old such regulator and draw the diagram :)
 
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