Small electric motor shorted out....why???

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  #1  
Old 03-07-06, 08:51 PM
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Unhappy Small electric motor shorted out....why???

Hi Forum,

I hope there is someone who would be willing to give me advice.

I have a small electric motor (about 1" by 1") that I am trying to use to get an antique phone working again. The motor used to ring the bell in an AT&T handset. It basically goes off when attached to a small card when there is an incoming call.

After finally getting it into the antique phone, I was dismayed to find out that the motor suddenly doesn't work anymore. Has this ever happened to anyone? I have seen this occur with small 12V motors before where if they are hooked up backwards or incorrectly they 'short out'.

Does this mean the motor is ruined, or is there some way to get them 'shorted back' or working? I am amazed that they can break so easily. It is very difficult to find a small motor like this one again, so I'd appreciate any help! Thanks

jpasquini
 

Last edited by John Nelson; 03-08-06 at 08:57 AM.
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  #2  
Old 03-07-06, 10:30 PM
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my best guess is that you had a voltage mis-match. Either you had insufficient voltage to drive the motor, or too much voltage was applied and the motor was fried. My guess is that the latter occurred, since it was working at one point. If true, you'll either have to rewind the old motor, or get a new one.
 
  #3  
Old 03-07-06, 10:39 PM
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> I have seen this occur with small 12V motors before where if they are hooked up
> backwards or incorrectly they 'short out'.

Always use a fuse less than the locked rotor amperage.


> Does this mean the motor is ruined

Does it smell bad?
Did you test the resistance?

If you spin it by hand (stretch a long string or broken rubber band over the pull to spin it fast) will it start? Does it generate voltage?


> is there some way to get them 'shorted back' or working?

Rewind the stator.

The "card" (PC board?) should have a fuse in series with the motor windings.
 
  #4  
Old 03-07-06, 11:00 PM
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bolide,

How do you rewind the stator?
This little motor basically has 2 bar magnets, one on each side, and a small motor in the center.
There is a metal pin that runs through the center of the motor, pointed at each end. The motor sits inside the bell cup of the telephone.

When the current comes through (incoming phone call), the pin vibrates/moves back and forth, making the bell ring. The motor is attached to a small PC-like card which basically amps the phone signal up into a current to make the motor run.

OK so all this worked fine until suddenly this little motor decided it is dead. No burning, no sparks, just shorted out. I know the "card" is fine because if you hook a phone speaker up to it, it will still make a phone ringing sound.

I've had similar experiences with these little motors where they just short out suddenly, and I've always wondered why. You wonder if maybe you ran an alternate current through them if they would 'flip back'. Or maybe that's just crazy talk...............


 

Last edited by jpasquini; 03-07-06 at 11:16 PM.
  #5  
Old 03-08-06, 12:27 AM
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Originally Posted by jpasquini
How do you rewind the stator?
Very painstakingly with enameled wire. Could take 1000 turns each and you have to count them.


> You wonder if maybe you ran an alternate current through them if they would 'flip back'.
> Or maybe that's just crazy talk...............
Just crazy.
 
  #6  
Old 03-08-06, 07:51 AM
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I know quite a bit about telephones, but not about truly ancient one, so I don't know if this will help. I am not familiar with any "motor" used as a ringer in phones from the 1920's onward. The ringer was a solenoid-type coil with a clapper attached to the armature. The ring signal is an AC voltage, which caused the clapper to flap back and forth, striking the bell.

The ring voltage at the telephone is minimum 40 Vrms up to as much as 80 or 90 Vrms.

AT&T used principally a 20 Hz ring frequency. Party lines, which especially later in the 20th century were mainly the domain of the smaller independent telcos like GTE, etc. used different ring fequencies so that only the phone at the party called would ring. A capacitor and some other modifications to the ringer in your phone would cause it to ring only at one specific frequency. The frequencies used were 16 2/3, 20,25,30,33 1/3, 40,42,50,60, 66 2/3

Telephone collecting is popular. You will find much info on the web, and undoubtedly could find a replacement part for your phone. In addition, you need to find out if your ringer is in fact a 20 hz ringer. If not, it may not respond to a ring today. Also, you need to verify the wiring. Modern phones used tip-to-ring connections ( 2 wire phone line). But party line systems sometimes used a 3 wire phone line with gounded ringing. So, the ringer might need to be tip-to-ground or ring-to-ground.

I am not a collector or tinkerer. But my grandfather and 2 great uncles between them put in over 100 years of service with AT&T, beginning in the 1890's. So, I guess it's in the blood. I also worked for a telephone manufacturer ( Telequest) in the late '80s.
 
  #7  
Old 03-08-06, 10:34 AM
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Well actually all I did was take a motor out of an old 'slimline' telephone. Now when I say motor, I'm sure it's not a term a true antique phone collector would use.

If you have one of the older phones with a REAL bell from the 80's (it's a shame all the new ones have a digital speaker, it's just not the same) try opening the bottom and taking a look sometime. In my limited experience I've seen as many different creative ways of making the bell ring as the phones I've looked at. Usually there's a small 1" cylinder motor involved and some hammer and springs.

This antique phone has 2 large bells at the bottom and a hand crank, but they don't work. So, what I originally did was get a 'motor' mechanism from an 80's slimline........ which in this case turned out to be a little round one that fit right inside one of the bells. That way, the phone would actually ring when someone calls.

Then suddenly it burned out. I managed to find another 'slimline' telephone and this one had the motor above with the vibrating pin. It also fit inside the bell cup with its own bell, hidden. It was in a really crappy plastic handheld phone but it had a wonderful tone. (The AT&T desk phones from the old monopoly days have dual bells, those are kind of cool but not workable). But then after mounting it, the motor turned 'off' like the other one.

I just don't get why these little motors burn out so easily, there must be some way to bring them back. It's like working with eggs. Well, off to find another old telephone motor and try #3. I'll leave a swath of dead phones behind.

:glocke: Its an interesting little project. Just thought I'd give the rest of the story.
 
  #8  
Old 03-08-06, 07:28 PM
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OK, it is clear now that you have a ringer solenoid, not a motor. This is an AC device. It will always have a capacitor in series with it. The value of the capacitor may vary the ring frequency, as I mentioned before. But, it must have a capacitor in series. This device is nearly a short circuit across the DC tip/ring voltage. You must find out where in your old phone the capactitor is, or is should be, and make sure you are wired correctly.
 
  #9  
Old 03-09-06, 06:39 PM
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Thanks everyone for your advice. I took no chances this time and took the capacitor that came with the solenoid off an old $3 bell telephone. For anyone interested, the phone kind of looks like the one on this page:

http://www.gadgetuniverse.com/images/p0004651v.JPG


and now it rings! Now I just need ear plugs.......
 
  #10  
Old 03-09-06, 07:07 PM
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Or, for those who prefer, the "Enron executive" version..........

http://www.telephoneteca.com/artelgallery.htm

 
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