Speed Motor Control without PWM by Potentiometer

Hi All

I have a question. can I control the speed of 12 v dc motor by Lm293 IC and Variable resistor.

I want to do this without PWM and just by Variable Resistor.

Thanks in advance

There is no such IC as an LM293. You are probably talking about an L293 which has four push-pull switches that are on and off with logic and controlled with PWM, not linear with a variable resistor.
About 100 years ago they used a huge heavy very expensive variable resistor to poorly control the speed of a 12VDC motor. The variable resistor got very hot.

A high power potentiometer was also called a rheostat
"back in the day". Idea being that you were controlling
the current flow (rheo-) more than the applied voltage
(potentio-) although the two are obviously related.

"Can" you? Sure. Over some range, with some large
waste heat and probably a brief bad smell followed
by small fireworks. A well designed big-heat-sink
linear amplifier could be controlled by a potentiometer
if you really, really wanted to forego switching driver
efficiency.

Then again there are many PWM chips that will let
you apply a voltage to the error amp + input and
feed EAOUT to FB, and get a fairly linear(ized) duty
cycle vs voltage transfer function. Range may or
may not include zero....

Hi,

Can you give an explanation why you want to do it the old, poor, power consuming way?
Where is the benefit?

Klaus

No doubt the potentiometer will burn at some position, probably at a low ohm setting. You'll know when you hear a sizzling sound and smell acrid smoke. They are not made to pass much current. However you can use a transistor as a variable resistor. A potentiometer is suitable for applying a range of bias current, from full-Off to full-On. I use this method in my own homebrew power supply.

The LM293 is a comparator, not much use here at all.

As other have pointed out, the simplest speed control is by adding resistance in series with the motor power feed. The problem is twofold, firstly, much of the excess power is dumped in the resistance and secondly, it makes the motor speed more vulnerable to the load on it. For example, adding a mechanical load to a 12V motor when it is fed directly from 6V will slow it down. Adding the same load to the same motor fed from 12V but with a resistor to drop it to 6V will slow it much more or even stop it.

The reason is that a motor will draw more current as it's load increases, if the power source can provide it, the motor input power will increase. If the resistor limits the power it can draw, the voltage goes down instead and the motor might stall.

Tell us: do you need to control the speed or the motor power? If you need to control the speed, either by analog methods or PWM, you need a feedback mechanism that controls the motor voltage from the shaft speed so it can regulate itself.

Brian.

Mak2100 said:

Hi All
I want to do this without PWM and just by Variable Resistor.

Thanks in advance

Click to expand...

Why would you want to do this?