Why does a hammer make my electric motor work?

[ScottInso]

I have an electric lawnmower motor which doesn't like to start
-but when I tap the center shaft lightly with a hammer it almost starts, as I jostle the unit around it continues to almost start
-but when I really wack the center shaft, then it starts fine and runs Ok until it cools down, then it doesn't restart

it this a deep mystery about electric motors or and obvious part that need to be replace?

Big thanks for this forum and anyone who care to help

 

[itsmoked]

It likely has carbon brushes and they're either worn out and need replacing or are so clogged with debris that they are NOT reliably contacting the armature commutator bars. Whacking the shaft allows just enough bar/brush movement to get something going. This will shortly cease to work.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Bill West]

Knowing that earned me a bottle of the good stuff one time. Our hobby group had a place in the woods with a very senior resident caretaker. The starter on his old car got intermittent preventing him from going into the local town. Buddy and I jacked the car up in the mud, pulled the starter, flipped the beveled brushes over in the holders and in 15 minutes he was good for another year.

Bill

 

[dArsonval]

A Hammer and a Mallet are very useful tools in getting an electrical apparatus to obey.
The "blows", the impacts... they jostle electrical connections. They "jiggle" things around.

It takes a life-time of field experience to fully understand the use of these primitive tools.
They work just like the words uttered during their use. [They are very effective ; )

John

 

[JASGripen]

If you feel confident you can take apart the electric motor and clean the surfaces of the stator and rotor.
You probably got it wet and rusted a little just enough to prevent it from starting to spin. I have seen this on pump motors where it seizes up after prolonged time of heavy water condensation in humid environments or from lack of use.

I might be wrong but you should mow your lawn more often to prevent this from occurring.
Hammers are very good on starters in an emergency, but by the time you get to the sledge hammer you should probably replace the starter =).

 

[waross]

It depends. You don't always use a hammer.
My old Ford station wagon with a loose screw that mounted and grounded the starter solenoid.
Usually it started but not always.
If it didn't start i honked the horn and the vibration may allow it to make contact and start the engine.
Sometimes not.
Stage two. Kick the underside of the dash board. Then it would usually start.
Sometimes not.
Last stage. Get out, walk around and kick the right front fender.
That always worked.

A customer complained that his Automatic Transfer Switch was making a loud noise.
The ATS was based on a pair of magnetic contactors. When a magnetic contactor does not seat properly it vibrates and makes a lot of noise.
I made a fist and then hit the side of the ATS enclosure with the side of my fist. Hard.
The impact caused the contactor to seat and all the noise went away.

I almost forgot the intermittent relay in a mill. I located the panel by hitting the panel supports with a 2x4.
Once I found the panel containing the faulty relay I used a heavy screwdriver handle to hit the relays in turn until I located the bad relay.

Oh and I forgot about the power threader that the boys started with a hammer.
A new threader was delivered to a job site.
One of the electricians was a hard worker but not very bright.
The old Rigid Threaders had a multi prong plug between the switch and the motor.
If the switch or motor needed to be replaced it was plug and play.
The boys decided to have some fun and pulled the plug, under the machine, partly apart.
Our friend tried to start it and it wouldn't start.
One of the pranksters stepped up to help him while holding a three pound hammer.
Our friend became upset that the new machine may be damaged by the hammer.
He was reassured.
"Don't worry, the residual magnetism gets cross-fluxed and the electrons get saturated. It just takes a gentle tap to unflux it and it will start."
Our friend had his eyes on the hammer and didn't notice that the prankster had one hand under the machine.
As he gave the machine a gentle tap he squeezed the plug together and the threader started.
The boys started the machine for our friend a couple of times and were set for another start when they saw the executives from the head office approaching on a site tour.
Everyone faded out of site except our friend. He had a pipe to thread and carried on.
As the group came up to him, he smiled and turned the machine on.
Nothing happened.
He picked up the three pound hammer, smiled at the executives and gave the machine a gentle tap.
Nothing happened.
He hit it harder and nothing happened.
He panicked and started beating on the machine with the three pound hammer.
The tour looked at each other and left as fast as they could.

Moral. The hammer won't always work.


Welcome to the fraternity.
You have discovered an effective and valuable trouble shooting technique.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Field Service rates:
Using a hammer to get your motor working: $5.00
Knowing exactly WHERE to hit the motor with the hammer: $500.00


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[JASGripen]

Is there a "special" motor repair hammer?

 

[waross]

It depends on the size of the motor.
The hammer should never be more than 10% of the mass of the motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dArsonval]

JASGripen asked a question I feel I'm able to answer accurately.

There is a rather popular size "hammer" used in motor repair shops.

It is the Number 5 Garland rawhide mallet. It (and other sizes) are a favorite used by professional electric motor mechanics.

John

 

[dArsonval]

Finding some more photographic examples.
Here's a shot showing the classic Garland mallet(s) resting on a bench-top used in electric motor repair.

John