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'[EE] Motor overload protection problem'
2011\06\06@212337 by IVP

face picon face
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 thoug

2011\06\06@215736 by Carl Denk

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

On 6/6/2011 9:23 PM, IVP wrote:
{Quote hidden}

>

2011\06\06@222258 by IVP

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> What kind of amperage  is it pulling ?

Plate says 1.9A but not actually measured it

And I forgot - we're into the 2010's now so the whole thing will
be more like 50 years old, not 40

> And is the speed good ?

Comparing the sound with my lathe motor (1/3hp, 1425rpm) it
seems to be OK and steady. It doesn't sound like it's straining
and the end-plate turns, so it's likely not the gearbox. It's a fairly
heavy and messy job removing the gearbox (wet sump) so I'm
reluctant to dismantle it any further than I have to at this stage
but push will come to shove at some time in the near future

Jo

2011\06\06@223212 by Bob Blick

face
flavicon
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On Tue, 07 Jun 2011 13:23 +1200, "IVP"  wrote:

> 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

>
> 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.
Starting switch or starting relay is stuck or bad, most likely.

Cheers,

Bob

-- http://www.fastmail.fm - mmm... Fastmail...

2011\06\06@224020 by Bob Blick

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Or if it is a capacitor-run motor, rather than capacitor-start, it could
be a shorted capacitor.

On Mon, 06 Jun 2011 19:32 -0700, "Bob Blick" wrote:
{Quote hidden}

-- http://www.fastmail.fm - One of many happy users:
 http://www.fastmail.fm/docs/quotes.html

2011\06\06@224437 by Brent Brown

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On Tue, 07 Jun 2011 13:23 +1200, "IVP"  wrote:
> 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
>
> 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.
Hi Joe,

My first thought was it might be a synchronous motor as it's used in a timepiece (deos it say 1500RPM on the faceplate instead of the usual 1425-1475?), in which case it might be cap run instead of cap start, without a centrifugal starting switch. Faulty cap may cause it to run hotter than normal and trip the automatic overload protection device/circuit?

-- Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  spam_OUTbrent.brownTakeThisOuTspamclear.net.nz

2011\06\07@005345 by IVP

face picon face
> (deos it say 1500RPM on the faceplate instead of the
> usual 1425-1475

No, definitely 1425

After talking with the customer I'm informed that the motor itself
was overhauled in Nov 2003. The company which did this is no
longer around and so no one knows exactly what work was done

Perhaps they just did the 'roughly' bit of thoroughly

To me, some of the fittings and wiring look pretty ropey and a
lot older than 8, so if it was re-conditioned why would the original
wire be kept

I need to find out if the owner (City Council and interested parties)
wanted to keep it authentic. $ to $$$$$$$$ differenc

2011\06\08@013908 by IVP

face picon face
Thanks for the replies

I'll be passing it on to a friend of Russell who has more
expertise with motors. I'm sure I could find the fault, but
then what. An interesting job, but on second thoughts not
something I really want to get too involved with

Jo

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