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Electric motor problem

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stereotype - 25 Jul 2007 20:47 GMT
I have a small drilling machine driven by a 1/4 HP induction moto
(British)  sometimes it fails to start and just hums, if I switch of
and try again normally it runs. This happens not on a regular basis
sometimes it goes for days OK then plays up. Is there some sort o
maintenance needed?  Davi

--
stereotyp
John Stevenson - 25 Jul 2007 21:43 GMT
>I have a small drilling machine driven by a 1/4 HP induction motor
>(British)  sometimes it fails to start and just hums, if I switch off
>and try again normally it runs. This happens not on a regular basis,
>sometimes it goes for days OK then plays up. Is there some sort of
>maintenance needed?  David

What tune does it hum ?
David Powell - 26 Jul 2007 18:40 GMT
In article <vhdfa350t18719r9nnm80r98vlv2b2ccg7@4ax.com>,  
John Stevenson <john@stevenson-engineers.co.uk>  in
uk.rec.models.engineering wrote:

>>I have a small drilling machine driven by a 1/4 HP induction motor
>>(British)  sometimes it fails to start and just hums, if I switch off
[quoted text clipped - 3 lines]
>
>What tune does it hum ?

Anything, it doesn't know the words, so it has to hum.

Regards,

David P.
dave sanderson - 25 Jul 2007 21:45 GMT
> I have a small drilling machine driven by a 1/4 HP induction motor
> (British)  sometimes it fails to start and just hums, if I switch off
> and try again normally it runs. This happens not on a regular basis,
> sometimes it goes for days OK then plays up. Is there some sort of
> maintenance needed?  David

sounds like the start /run cap is on its way out. when its not working
if you spin it up by hand does it run?
new caps are quite cheap.

of course I could be wrong, no doubt someone more knowledgeable will
be along shortly.

Dave
ChrisQuayle - 25 Jul 2007 22:25 GMT
> I have a small drilling machine driven by a 1/4 HP induction motor
> (British)  sometimes it fails to start and just hums, if I switch off
> and try again normally it runs. This happens not on a regular basis,
> sometimes it goes for days OK then plays up. Is there some sort of
> maintenance needed?  David

Check all the wiring for continuity and tight connections first,
especially the leads that go into the motor terminals. They can
sometimes work loose on older motors. As someone else said, after that,
it's most likely the start capacitor, or it's wiring...

Chris
Don Young - 26 Jul 2007 04:56 GMT
> I have a small drilling machine driven by a 1/4 HP induction motor
> (British)  sometimes it fails to start and just hums, if I switch off
> and try again normally it runs. This happens not on a regular basis,
> sometimes it goes for days OK then plays up. Is there some sort of
> maintenance needed?  David

If it has a centrifugal starting switch (you can hear a click when it starts
and again when it is nearly stopped) the switch contacts and the mechanism
to operate it can be in need of cleaning. This usually requires disassembly
of the motor. No lubrication is normally used.

Don Young, USA
stereotype - 26 Jul 2007 20:21 GMT
Don Young Wrote:

> > I have a small drilling machine driven by a 1/4 HP induction motor
> > (British)  sometimes it fails to start and just hums, if I switc
[quoted text clipped - 21 lines]
>
> Don Young, USA
Thanks for all your input, yes Don it is a cetrifugal start motor, i'l
take it apart and check the contacts. Davi

--
stereotyp
eskimobob - 28 Jul 2007 20:21 GMT
I have this problem on two bits of kit I have just bought second
hand.  I can clearly hear that the centrifugal switch does not always
'click' back in when the motor stops so I assume that some lubrication
is required.  I'm planning on investigating further when I get some
enthusiasm...
Don Young - 29 Jul 2007 03:01 GMT
>I have this problem on two bits of kit I have just bought second
> hand.  I can clearly hear that the centrifugal switch does not always
> 'click' back in when the motor stops so I assume that some lubrication
> is required.  I'm planning on investigating further when I get some
> enthusiasm...

I think cleaning is called for but I do not think that these mechanisms are
generally lubricated. It might be ok in an enclosed motor where the dirt is
kept out if no lubricant gets on the switch contacts.

Don Young, USA
Bob Minchin - 29 Jul 2007 10:42 GMT
> I have this problem on two bits of kit I have just bought second
> hand.  I can clearly hear that the centrifugal switch does not always
> 'click' back in when the motor stops so I assume that some lubrication
> is required.  I'm planning on investigating further when I get some
> enthusiasm...

Lubrication is normally the enemy of these switches as it harbours dirt.
Complete cleanliness is normally the the best way IMHO

Bob
MikeH_QB - 26 Jul 2007 12:09 GMT
> I have a small drilling machine driven by a 1/4 HP induction motor
> (British)  sometimes it fails to start and just hums, if I switch off
[quoted text clipped - 7 lines]
> stereotype's Profile:http://www.rcgroups.com/forums/member.php?u=119209
> View this thread:http://www.rcgroups.com/forums/showthread.php?t=718458

Pretty sure it the cap that's getting old & 'leaky'. Hasn't failed
altogether as it would never start or possibly blow mains fuse. They
just get a bit worn out sometimes. Your cheapest and quickest option
is to replace the cap, they don't cost much and are (normally)
external so dead easy to get access to & replace. Tip - just be
careful fiddling with any connections if you have recently attempted
to start it, as the cap may hold a nasty residual charge which might
make your hair stand on end, eyes light up and teeth rattle a bit!

Mike
 
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