Running DC Motor without Arduino

I was trying to power a '130 size' DC motor without an Arduino, using only a breadboard power supply (5V). However the power supply seems to get hot after a few seconds.

So I tried using resistors but even the smallest resistor would stop the motor entirely. Then I tried a potentiometer but that started to smell funny after a few seconds. I also tried an L293d, now the motor was slower but the power supply got hot again.

The power supply is not supposed to get hot, right? Why did using resistors not work out? Am I approaching this completely wrong?

In general you cannot control the power to a motor with a resistor. Maybe if you have a very low value resistor (say 5 ohms) with a high wattage it might work but it is very wasteful of energy, and the resistor will get hot. Read up about Ohm’s Law.

If the power supply gets hot it is because the motor is drawing more current than the power supply is designed to supply.

Try testing the motor with a pack of 3 x AA Alkaline cells (4.5v) or 4 cells (6v). If you have a multimeter that can measure up to 10 amps them try measuring the motor current when powering it with the batteries.

…R

Power supplies have two ratings, not just voltage. There's also maximum current. So what is the current rating of your 5V power supply? It's also important what load you have on the motor, because that determines how much current it needs.

Steve

Many thanks for the replies!

Robin2:
In general you cannot control the power to a motor with a resistor. Maybe if you have a very low value resistor (say 5 ohms) with a high wattage it might work but it is very wasteful of energy, and the resistor will get hot. Read up about Ohm's Law.

Somehow I hoped that increasing the resistance would decrease the current, but apparently, that's not how it works. So how does it work when I control the motor with PWM? Then it just alternates between drawing zero and too much power?

Try testing the motor with a pack of 3 x AA Alkaline cells (4.5v) or 4 cells (6v). If you have a multimeter that can measure up to 10 amps them try measuring the motor current when powering it with the batteries.

I tried a 9V battery, but then the motor would not move at all. I will be looking for a multimeter soon.

slipstick:
Power supplies have two ratings, not just voltage. There's also maximum current. So what is the current rating of your 5V power supply? It's also important what load you have on the motor, because that determines how much current it needs.

I'm using an MB102, which according to the data sheet has a "Maximum output current: 700 mA". The Motor was running with no load. The motor data sheet says "No-load Current: 70 mA max".

derari:
Many thanks for the replies!
Somehow I hoped that increasing the resistance would decrease the current, but apparently, that's not how it works.

That is how it works. But you need to have a very low-value resistor or else the current is reduced so much that the motor can't work.

I'm using an MB102, which according to the data sheet has a "Maximum output current: 700 mA". The Motor was running with no load. The motor data sheet says "No-load Current: 70 mA max".

That suggests that the power supply should be OK - but it would be wise to measure the actual current being drawn by the motor.

Sometimes "maximum output current" is the max for a short period - such as 5 seconds - and the continuous current can be a lot less.

...R

Increasing the resistance does decrease the current, but that's not how we do power electronics any more,
because it wastes lots of power whereas PWM can easily be 95%+ efficient.

For battery use wasting power = less battery life, otherwise it means lots of waste heat to get rid of (which
generally means electronics less reliable and much larger and heavier and hotter and noisier).

Modern switch mode power conversion can handle kW of power in a surprizingly small space and weight,
PWM control of motors is one of the simplest examples of switch-mode power conversion.

Robin2:
That suggests that the power supply should be OK - but it would be wise to measure the actual current being drawn by the motor.

Ok, I measured the current. When powered with the AC adapter, the motor uses between 1 and 1.6A. When powered by a battery, it uses 0.35A (and does not move). Both numbers are without load.

Since this is clearly outside the supposed range (70mA no load, 500mA stalled), this means the motor is damaged in some way, right?

derari:
Ok, I measured the current. When powered with the AC adapter, the motor uses between 1 and 1.6A. When powered by a battery, it uses 0.35A (and does not move). Both numbers are without load.

Since this is clearly outside the supposed range (70mA no load, 500mA stalled), this means the motor is damaged in some way, right?

if the motor rotates with one power supply then it is unlikely to be faulty.

If you want help you need to be more precise.

What is the output voltage and current for the AC adapter?
Is the AC adapter designed to output AC or DC?

Exactly what battery did you try?

...R

Now I measured all components

The AC/DC adapter provides 9V and 0.5A (according to the data sheet it should go up to 1A). With the adapter, I measured 5V and 2.5A on the breadboard power supply.

The battery is 9V and 0.35A. The power supply with battery is 5V and 0.5A.

I hope this helps to shed some light on my issues.

Robin2:
if the motor rotates with one power supply then it is unlikely to be faulty.

If I understand correctly, the motor should not draw 0.35A without moving (without load).

If the AC/DC adapter is supposed to produce 9v and is only producing 5v it means that you are very seriously overloading it and it will probably go on fire.

Why not follow the advice about batteries that I gave you in Reply #1

...R