Most likely the motor has a thermal overload switch that is going bad,=20
tripping at too low a temperature. Probably means a new motor, or if=20
it's a very special, likely rewind the coils and replace the thermal. My=20
wifes kitchen range hood fan motor has that issue. Has been=20
intermittent, thought it was the variable speed control. But then it got=20
worst, and was able to trouble shoot to the point, there was power to=20
the motor, and it didn't run. Pulled the motor with squirrel cage=20
blower. It ran fine on the bench with no enclosure, so I went up on the=20
roof (where it is mounted) installed it, and it ran about 5 seconds=20
before quitting. Back on the bench it ran fine. New motor on order,=20
should be here mid week. Also could be an intermittent winding or=20
shorted winding causing excessive heat.  Could it be that bearing is=20
causing excessive force. Sounds like time for a new motor, if available.=20
What kind of amperage  is it pulling? And is the speed good?

On 6/6/2011 9:23 PM, IVP wrote:
> Hi all,
>
> I'm servicing and refurbishing a large floral clock (the one in
> Auckland's Albert Park for those who might know it). Part of
> the reason for doing so is that recently it's been stop-starting
>
> I've got the motor and gearbox at home now
>
> http://home.clear.net.nz/pages/joecolquitt/mvm.html
>
> It's a Metropolitan Vickers BC 2408. Fairly typical appliance-
> type single-phase motor, 230V 1/4hp 1425rpm, with reduction
> gearing and end-plate to drive the minute hand, which isn't that
> minute BTW
>
> http://en.wikipedia.org/wiki/Metropolitan-Vickers
>
> I suspect that the problem is overheating. The motor runs but
> after perhaps 20 seconds from cold it turns off. When it restarts
> some seconds later the time until the next stop becomes
> progressively shorter. The motor does seem to be hotter than
> you'd expect after only a short run time. I think I detect a little
> knocking, which could be a bearing. It does run 24/7 after all,
> and has done for many years. Everything is at least 40 years
> old so I'm told
>
> I can identify the start cap, but the other two devices are not
> familiar to me. The black box (actually a deteriorating plastic
> cover on a yellow box) above the start cap and a two-terminal
> something behind the 'Warning' cover on the end of the motor
>
> When the motor stops there are two clicks. I presume the first
> is the protection relay dropping out, the second would be the
> motor's internal centrifugal switch. I can't tell where exactly the
> first click comes from though
>
> So, questions -
>
> Would the wires on the bottom of the yellow box (picture 4) be
> some sort of thermocouple ?
>
> Even if a bearing is worn, would you think that could cause so
> much heating in a few seconds to trip the protection ? There's a
> service tag for the gearbox dated Nov 03 (possibly just an oil
> change), but the motor appears untouched. As you can see, the
> wiring is getting a bit scruffy and could do with replacing. One
> obvious option would be to get a new motor. An ordinary one
> such as this can be had quite cheaply, but I'm still keen to learn
> what could be wrong with the present one
>
> TIA
>
> Joe
>
> As an aside, much of my youth was mis-spent on the abandoned
> pier next to Fort Gilkicker in the south of England. It had several
> ancient Metropolitan Vickers electric cranes. I took a large brass
> name plates off a motor, had it polished and lacquered and made
> into one fine-looking, if ridiculous in hindsight, belt buckle
>
> http://en.wikipedia.org/wiki/Stokes_Bay
> http://en.wikipedia.org/wiki/Fort_Gilkicker
>
> I did hear that the pier was used by Queen Victoria's train as part
> of her visits to Osborne House on the IOW. Doubt my crane was
> there to lift her luggage though
>   =20
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.