If an electric motor starts making a horrible noise, or it just stops, what do you do. Is it broken, is it repairable?
The article below, sets out to describe easy electric motor fault finding & diagnosis (without a test meter). What to look for, when trying to identify an issue. Why it’s stopped, why it’s making a horrible noise, or why it’s not going very fast… So hopefully, it will help you decide if an item is repairable, or destined for the junkyard!
We can break the motor diagnosis down into four distinct groups:
* Electricity can Kill *
As with any electrical device…
Make sure the power is disconnected before examining by:
Video giving hints and tips on fault finding an electric motor:
If the motor smells horrible, it’s usually a bad sign. It’s often because the motor has got too hot. The windings (wire) in an electric motor are covered in a varnish, the insulation is often made of plastic and has started to melt. Burnt varnish & plastic stinks. Dependant on how hot the electric motor has got (and for how long), it may be too late! The insulation may have broken down and shorts in the wiring may have occurred?
If something has burnt out, this can often mean it’s too expensive to repair. However… It may be worth checking, (Just in case the motor was switched off before it fully overheated)?
An electric motor in a bad state, may be unsafe to use… The insulation may have partly broken down and may start to fail under load.
If it’s safe to run the motor…
Does it sounds a bit rough? If the motor rotates, sound is a good indicator of where a fault may lie…
If you see smoke (or feel heat) it can be dangerous! The motor could be about to catch fire..!
The noise can come from a number of places (in no particular order)…
Can make noise due to:
They can be cleaned, or flushed out with a thin spray oil, then more oil or grease applied. Or, they can be replace with new, (info on replacing bearings can be found in the following article – How to Measure & Buy a Replacement Bearing ).
The noise can also come from…
Dust and debris can get in and clog up all sorts of places. It can block airflow for cooling, get into switches and speed controllers and cause the motor to rub and bind against the casing. In the case of ventilation fans, it can stop the fan blades rotating.
Clean out and make sure the motor can breathe (cooling). Prevent obstructions that slow or stop the motor from turning.
If the brushes are worn, they can cause more sparking, erratic running of the motor, juddering, etc. This can make additional noise.
If the commutator is worn or dirty (usually carbon dust from the brushes, or from sparking). The lack of electrical contact, or rough a rough running surface can cause erratic running, slow speed and additional noise.
Can be caused by any of the reasons above, but may also be due to impending doom! If there are any faults, or the insulation is starting to break down, the motor may start misbehaving, drawing more current, making more noise.
Some times the rotating speed can create vibrations (especially fan blades).
Things to look out for:
Has something come undone. Is it rattling around inside the casing?
Something bent, or not assembled correctly? It’s not unknown for a motor casing not to be correctly re-assembled after being taken apart. Especially with power tools and their plastic casings that can flex prior to assembly. A slight misalignment when screwing back together could mean something starts to rub, misalignment of the brushes, etc.
Carbon brushes pass electricity to the motor armature.
Please note that you can get more expensive (and often more reliable) brushless electric motors.
So, carbon brushes aren’t always fitted.
Electric motor carbon brushes are often housed in brush holders. These allow the brushes to slide in and out (with the aid of a spring). As the brushes wear, they are pushed by the spring against the armature to ensure there is electrical contact.
Just remember that…
If it works, it’s only a temporary fix. A repair must be made as soon as possible, or more damage may occur…
If the carbon brushes are worn, they can…
If the electric motor is run in this state, it could start running on the springs, damaging the armature?
A double edged sword… Sometimes the brushes can damage the armature, sometimes the armature can damage the brushes!
If the brushes wear away completely, the motor can end up running on the springs. The brush springs are a lot harder than carbon and and can wear the commutator. In most cases the springs can short out and blow the commutators, causing complete failure. Therefore, don’t run the motor on the springs, (you can usually tell by the noise and excessive arcing).
If the armature commutator is worn or dirty:
(or, it’s a Brushless Electric Motor?)
If yes, then it could be a defective starting capacitor. The capacitor gives the motor an additional boost to get it spinning. Once running, the motor has its own momentum to keep it going.
It can be a simple fix to replace the starting capacitor.
Please note that not all electric motors are fitted with Thermal protection...
Some electric motors are fitted with thermal trip to protect the motor from overheating. They are often placed near to the motor windings, where heat can be generated.
The are often two types of thermal Protection:
Resettable thermal trips break the supply to the electric motor. The resetting process often requires you to wait for the motor to cool.
Non-resettable (a fuse):
Non-resettable thermal fuses are often quite small, so it may not be immediately obvious that the motor has one fitted.
I’m using the term ‘Gizmo’s’ for any additional items, bells and whistles that may be fitted to an electric motor…
Switches, speed control and gizmo’s can go defective. There can be a number of reasons why, and the list is not exhaustive.
Generally, all you can do is check for the usual electrical faults. However, electric motors generate heat and often have a fan to draw in air for cooling. These fans pull in dust and debris which can cause issues. If the motor is used in a process that generates dust, then there may be even more of an issue?
If you’re not sure what you need, sometime it’s a good idea to have a look? The list below may give you an idea of what’s what’s available, what to look for and how much it costs…
Carbon Brushes, Bearings and Electric Motor Parts:
|Carbon Brushes||UK – https://ebay.us/cb4GSd|
|USA – https://ebay.us/G76O4P|
|AUS – https://ebay.us/99GlEP|
|Bearings||UK – https://ebay.us/M31arH|
|USA – https://ebay.us/psNjrB|
|AUS – https://ebay.us/gpFsei|
|Bushes||UK – https://ebay.us/I58idr|
|USA – https://ebay.us/s3y4UM|
|AUS – https://ebay.us/VvTMaU|
|Armature||UK – https://ebay.us/6mrh6j|
|USA – https://ebay.us/WRQAny|
|AUS – https://ebay.us/9ym1YY|
|Test Meter||UK – https://ebay.us/HuZBxX|
|USA – https://ebay.us/olyfrh|
|AUS – https://ebay.us/hW13GS|