# increasing life of DC motor

#### p_lin

Joined Aug 10, 2010
3
Hi,

I'm working on a project that uses a miniature pager motor (6 mm diameter) serving as an actuator for a feedback control system. It is a coreless DC brushed motor.

I read that the expected lifetime of these motors is only 100 hours and I'm looking for any recommended ways to increase the life span. Any ideas??

My application is switching directions, and I've reduced its operating voltage to 3.8 V (average ~2 V) -- motor is rated to 4.5 V. I think there could also be some arcing between the brushes and commutator that I can reduce. I've read a little about arc suppression circuits, would this help and how do I implement one?

some commercial vendors (e.g. maxon motor) rate their 6 mm brushed coreless motors to 500-1000 hr lifetime. But they cost 75 bucks! the pager motor I'm using is 3 dollars and works fine (other than the rated life). any thoughts would be appreciated!

#### mcgyvr

Joined Oct 15, 2009
5,394
what do you need for a lifespan?

#### p_lin

Joined Aug 10, 2010
3
what do you need for a lifespan?
I'd be happy with 200 hours, any more would be awesome

#### marshallf3

Joined Jul 26, 2010
2,358
First thing to do is add caps across the input terminals, both a low ESR electrolytic and a regular 0.1 uF or better disc/film cap.

Another plus would be a current limiter circuit, don't let the motor have any more than it needs to do its job.

#### p_lin

Joined Aug 10, 2010
3
First thing to do is add caps across the input terminals, both a low ESR electrolytic and a regular 0.1 uF or better disc/film cap.

Another plus would be a current limiter circuit, don't let the motor have any more than it needs to do its job.

Would the two capacitors need to be in parallel and with different values? What value would you suggest for the ESR electrolytic?

I'm controlling the motor with a microcontroller and a toshiba TB6612FNG motor driver. Can I just do the limiting in software (put an upper bound on the control signal's output)?

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#### marshallf3

Joined Jul 26, 2010
2,358
In parallel yes, and I'd go with something like 100 uF + 0.1 uF These would mainly serve to help absorb spikes and transients as the motor operated.

I'm unsure of how to work with these newfangled microcontrollers but a current limiter is just that, something adjustable that only allows a certain amount of current to flow in the output circuit, usually by limiting the output voltage. In doing so you won't be feeding any extra voltage or current to the motor that it doesn't need to do the job, thus power is kept at a minimum therefore strain on the device is also kept to a minimum.

#### Audioguru

Joined Dec 20, 2007
11,249
I think the simple bearings on the cheap motors will dry out (the oil) then the bearings will very quickly wear out.
The brushes and commutator will also quickly wear out.

#### marshallf3

Joined Jul 26, 2010
2,358
That happens too, but he just wants inexpensive ways to potentially increase the life of the motor. Unless you had a slew of them you ran until they failed then dissected them to find the most common nature of the failure all you can do is cover the easy bases.

Joined Jul 7, 2009
1,583
First find out what the failure mode is at the end of life (contact the manufacturer). Then see if you can do anything to eliminate that failure mode or increase its failure time. If the manufacturer won't respond or help, then put 5 or 10 motors on test and determine the failure mode(s) and lifetimes yourself.

You'll learn a lot from the effort -- and you'll know whether to continue to invest effort in this motor or pay more for something that meets your needs. The advice the others have given may or may not help -- but with failure information, you can know exactly what problem you're trying to fix.

#### Audioguru

Joined Dec 20, 2007
11,249
A pager motor does not run for a long time so compromises are made in its design to make it cheaper.
Electric model airplanes are powered with a similar motor but it is designed to last much longer than a pager motor. Hobby stores sell a little airplane motor for $11.99CAN to$14.99CAN.

#### SgtWookie

Joined Jul 17, 2007
22,221
If you are going to put more than about 1nF capacitance across the motor, and you are planning on using PWM, then you will also need to use an inductor between the IC and the motor, or you will risk burning out the IC very quickly.

The capacitor will appear as a dead short across the IC's outputs, particularly if the PWM is low-speed.