DC motor keeps wearing out

Hey there! I'm trying to do a very simple project where I have a DC motor run for roughly 10-12 hours a day continuously but I'm finding that after a week or two the motor will be noticeably weaker and eventually stall and then just not work anymore. I've changed out the motor twice already and they've all done the same thing.

The motor I'm using is a 6V 20RPM 7.5Kg.cm: Metal DC Geared Motor - 6V 20RPM 7.5Kg.cm -DFRobot

I have the logic on my Arduino Nano and to have a button to start/stop power to it, and then the motor is connected directly to a power source. It's connected to a chain and sprocket and it runs very smoothly the first few days of operation. Is it the load that's causing it to wear out over time? Would a different motor like a stepper be better for this application?

I know little about the application so can't comment on that particular motor's suitability.

Is the motor under a lot of load compared to its capability. I think that I would try a much stronger motor to see if it would live. Pololu has a line of quality motors.

What motor driver are you using?

Do you put any lubrication on the bearings? The exposed bearing shows it is a simple brass or bronze sleeve bearing. Without lub, you get what you are experiencing.
If the motor just quit , then the brushes would be suspect, but just slowing is bearing problem.

Paul

It sure is. Running a motor for such a long time, 10-12 hours likely exceeds the duty cycle of the motor. Many small motors self destruct by running for that long time. The cooling is not good enough, or is absent.
I've got a micro mill, an MF70. Measuring the spindle motor temperature, motor running without load, the temperature just keeps raising. Of course I toasted the first motor letting it work.

To run a motor like You do, 10 - 12 hours per day You really need to find a sturdy motor made for continuous running.

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Have you dissected one to see what "wore" out?

  • Brushes (not likely) wear is proportional to current.

  • Overheating, perhaps shorted inner windings, probably the most likely.

  • Mechanical, not likely from your description but could be bound up.

I would guess @Railroader hit the nail on the head. If the motor overheated it is possible (likely?) one or more of the inner windings heated enough for the wire insulation to break down. This would lead to a small number of shorted turns at that point.

Is the motor completely closed? If open can you add a small computer fan to cool it?

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@johnRob
Spot on. My motor was clearly overheated and the isolation in the rotor windings was toast, short circuited, inside. At the brushes and the collector there were sparcs like new years fireworks. The RPM of the motor was like twist and shake.
As I said, running the motor for a long time made the temperature curve point upwards without any sign of settling. That was measured on the new, spare part motor.
Heavy duty stuff is required for 10 - 12 hour continues running. Chinese hobby motors is the wrong choice.

Thanks for all the great replies!

I have an L298N motor driver, but after it's worn out even connecting it directly to a power supply it won't run. The motor seems to have a lot of lubrication on it already and it starts to become weak and slow and eventually quits.

I have dissected the gearbox and it doesn't look like a mechanical issue because the gears still turn freely.

The same motor I have used on applications where it isn't dragging along with a chain & sprocket and I've been able to run it for the 10-12 hours a day for up about a month now.

@Railroader now I'm wondering if running it intermittently (a few minutes on, a minute off) would help or if eventually I'll be back in the same place? I will be looking at some heavier duty stuff for sure. I started looking at stepper motors but maybe a heavy duty DC is more worth it?

The on / off ratio will have to be such that the rotor can cool down before restarting. It will have to be off much longer than on due to the poor heat transfer between the rotor windings (where the heat originates) and the outside world.

Any brushed motor will wear out if run continously even if its loaded lightly. Even if windings are intact, if not the brushes then the commutators will wear - faster or slower depends on the thickness or materials used.

The only brushed motors that last long are the small tape motors simply because of light duty, light construction and not-so-continuous usage.

Even so I have come across tape motors that have commutators worn to the extent that the motor intermittently stops - only its belt coupling with the flywheel maintains rotation but at the cost of speed variations.

IMHO, the only motors that can run continuously are ones that do not use brusher - bldc, stepper, or induction. That's why ACs and fridges use induction motors in them.

Any brushed motor will wear out if run continuously even if its loaded lightly. Even if windings are intact, if not the brushes then the commutators will wear - faster or slower depends on the thickness or materials used.

UPDATE: (some words were corrupted)

This statement is NOT valid for many motors. Our brush type fuel pump motor is rated to last 15 years or more at automotive usage rates. the difference is we pass the fuel through the motor to keep the windings cool.

What information did you use to inform the choice of this motor?
Realistically you need to know the amount of power it will be required to produce.
converting the units 7.5 Kg.cm = 0.73549875 Nm
and using the max figures (no load speed and stall torque) that is about 1.5 Watts.
again using the max quoted figures
Locked-rotor current: 0.6 A * 6V = 3.6 watts

That is very little power for doing any real work.
So the motor is working very hard and likely the internal gears will be getting very worn.
Basically you need a more powerful and robust motor.

Hi,
If you run the motor under no load then load it, is there a significant drop in speed.

What is the motor driving?
How much current does the motor consume under load?

Thanks.. Tom.. :grinning: :+1: :coffee: :australia:

Running on 6 Volts is max so it will get hot, and run not very long so use PWM to run it slower. and yes sometimes not lucky as it is a toy.

As far as I know, DC Motor connection with L293D Driver requires freewheeling diodes.
Hope this link helps : Understanding DC motor freewheeling

The "D" in L293D means that the diodes are built in.

The L293 lacks freewheeling diodes.

@TomGeorge If I run it under no load it reads about 35mA, and when I run it under load it seems to read up to 100 mA. There doesn't seem to be any drop in speed at first but over time it starts to have speed drops under load.

I can feel it heating up over time but it doesn't feel extremely hot and more of just a warmer temperature.

But it seems like the general consensus is a more robust motor so I'll be looking into that. Thanks everyone! :slight_smile:

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