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Problem with Single Phase Hoover AC Motor

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Stephen Ward 621/12/2014 15:36:25
7 forum posts
1 photos

Hi Guys

Having a problem with a single phase motor (Hoover 1/2 hp) that drives my Boxford Model A. It has been working fine however recently I have needed to turn the chuck before the motor will start otherwise the motor will just make a buzzing sound. Any suggestions as to what this might be.

I had thought that the capacitor could be the problem as it is quite an old
motor and I have checked that all connections are secure.

Regards

Stephen

Neil Wyatt21/12/2014 15:43:20
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19076 forum posts
736 photos
80 articles

My 1/3 Hp Hoover motor has a centrifugal switch that connect the starting winding (and the capacitor). Those symptoms sound like the switch sticking open.

Neil

john fletcher 121/12/2014 16:59:28
805 forum posts

The start circuit is open circuit an Neil says, and the weak point is the centrifugal switch. Capacitors are pretty reliable, never the less the do fail. If you have an old fluorescent light capacitor you could try a substitution initially. You could get your friendly electrician with his 500 DC insulation tester to care out a rudimentary test on your capacitor before removing the motor from the lathe.If you do have to take the motor to pieces you will find the switch is at the no drive end, so its a complete strip down. Mark both end of the motor using a scriber and steel rule two lines one end and one the other. These lines are to help with alignment when you re assemble the motor. with a bit of care you might be able to take out the through bolts and just ease out the drive end shield and rotor. The centrifugal switch actuating bits are attached to the rotor, they fly out due to centrifugal force against spring tension as the rotor speeds up. The assembly should be free to move, don't oil them. You will see the actual switch which is attached to the end shield, it might not be obvious how the thing works, the contacts might need a clean up with a bit of fine wet & dry,not too vigorous. As your motor is quite old so be careful with the wire insulation. It might be a good idea to get an electrician to give the motor an insulation test. When replacing the motor ensure you a have good sound earth, to the lathe and motor.Ted

Speedy Builder521/12/2014 18:32:25
2644 forum posts
218 photos

I have a similar problem with 3/4 Hp on my home made circular saw. Its laziness to the extreme. To get it to start, I 'tap' it with a hammer, then switch it on - works most times. As John says. I expect it is the centrifugal start switch. Mine is probably clogged with sawdust - waiting for a nice hot spark to set it alight!! This Christmas week I must strip it down and clean it, its probable that the contacts need cleaning at the same time.

Ashamed

Tony Simons21/12/2014 18:54:48
37 forum posts

You can normally hear the centrifugal switch click as the motor slows down. I have cured them temporally by squirting WD40 in there, either through the vents if its a vented motor or by gently separating the cover from the body to insert the WD40 straw. No substitute for stripping and cleaning though.

 

Edited By Tony Simons on 21/12/2014 18:55:36

Stephen Ward 622/12/2014 12:34:57
7 forum posts
1 photos

Guys thanks for your comments looks like I will be stripping it down over the Christmas break. The capacitor shows no obvious sign of damage so looks like it the switch.

Thanks again and have a great Christmas. Regards Stephen

WALLACE22/12/2014 12:57:19
304 forum posts
17 photos
I seem to remember there was a previous post regarding a Hoover motor with perished rubber interior wiring so a rewire job may be on the cards as well to keep it safe !



W.
Vic22/12/2014 13:51:58
3089 forum posts
16 photos

I had the same problem with my belt and disc sander, I had to give it a shove or even a few revolutions to start it. In the end it wouldn't start at all. A replacement Capacitor sorted the problem, the "ectoplasm" had leaked out of the old one by the look of it. laugh Maplins had a suitable replacement.

Speedy Builder523/12/2014 14:26:07
2644 forum posts
218 photos

All good advice above. Seems stupid, but do disconnect from the power supply (Don't just trust to it being switched off).

Remove the cover to the connections and note wire colours and positions - else you may re-connect it with a reverse direction or worse.
pc200032.jpg

Now mark the position of the end covers in relation to the frame.Unscrew the long bolts that hold the covers on - in this photo there are 4 of them. Remove the end cover at the junction box end - it may be stiff as you are pulling the bearing out of its housing. Be careful of the wires which will be attached to the switch plate attached to the cover which go to the field coils and capacitor.
pc200028.jpg

Unscrew the switch plate from the cover. In this photo, the switch contacts are just by my left finger. Clean these contacts with a bit of fine wet and dry. You may be able to 'spring' the contacts apart to make life easier.
Finally, clean the centrifugal mechanism and make sure it slides easily. Do not lubricate as this will only collect dust etc.
pc200031.jpg
Now re-assemble in the reverse order. Make sure that the rotor does not scrape any of the wires when assembled and that the 4 cover bolts are also clear of any wires.
Now you are ready for test. Once the mains wires are connected but not plugged in, use an ohm meter to check that there is NO CONTINUITY between frame earth and the live or neutral wires. If the motor is out of the machine and on the bench, hold it down with a clamp or suitable device and without touching the motor power it on and it should run up to speed immediately. With a neon tester, as a safety check make sure the frame of the motor is not live. If this all passes, I would say the job was a good one. Disconnect etc then.
Put the motor back into the machine making sure that all earth wires are connected and plug it back in, turn on and again check with a neon tester that the machine is not live. - Job done

 

 

Edited By Speedy Builder5 on 23/12/2014 14:28:50

Stephen Ward 626/12/2014 21:34:27
7 forum posts
1 photos

Hi Speedy

Thanks for those pics, always helpful.

Regards

Stephen

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