Post by thread:[EE] Motor overload protection problem

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

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}> 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 >

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

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.brownTakeThisOuTclear.net.nz