# Motor start switch sticking



## subelect (Nov 25, 2007)

I have a farmer who keeps having problems with his 10-12.5 hp, 240 volt, single phase aeration fan for his grain bin. 
The stationary start switch internal to the motor keeps sticking open. The contacts get warm enough that that attach themselves to the plastic N.O. portion of the switch.
The farmer did say that he saw wisps of smoke coming out of the motor when he tries to start it but it just hums at him. 
We take the fan apart in the shop, find the switch sticking, either clean it up or replace the plastic switch. Each time, we verify the correct operation of the movable start switch on the shaft and the capacitors (start & run) are intact. 
We cycle the fan multiple times in the shop and it works just fine.
I install it on the grain bin and it is good for one cycle. The next time you go to start it up, it has stuck in the open position.
The first 2 times, the farmer brought it to our shop. The last time, I took it to the bin and found the 100 amp fused disconnect inoperative. I replaced it and installed the fan. 
It worked just fine once; then it would not start the second time. This was after it was cycled several times in the shop. 
I checked the voltage (242 phase to phase), the connections, everything that I looked at was fine. Except for the twelve feet of 6/3 SO cord feeding the motor. That cord is rotting on the ends. If you twist the individual wires, the insulation crumbles off. The outer sheath of the wire looks okay, but the individual conductor insulation is no good.
But, that cord is not getting hot nor is it blowing the 100 amp fuses feeding it. 
I did not think about it at the time, but I should have meggered the SO cord to see if it is breaking down phase to phase or phase to grd. 
Is it possible that a rotting out cord could cause the motor start switch to get hot enough to stick in the NO position without blowing the fuses? 
If it was an open ckt or a low voltage condition, I would think that the magnetic starter would not stay latched in and chatter or just drop out completely. 
Have you ever come across a problem before?
Thanks,
Rick


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## subelect (Nov 25, 2007)

And, when we cycle the fan in the shop, it is in open air. So it is pulling harder trying to move air like that than when it is installed on the grain bin pushing air thru the ducts & grain. 
Basically, if the fan works in the shop, we are usually confident that it is going to work when we install it.
Rick


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## greenman (Apr 20, 2012)

contact cleaner?


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## Wirenuting (Sep 12, 2010)

Are you talking about the centrifugal switch sticking?
Can be caused by bad switch, dust or moisture build up, improperly orientated motor. If its to be installed horizontally don't put it vertically. 
Some of the cheaper non-OEM motors we have been getting have had all these problems over the years. 
Some of our smaller motors are 40+ years old and good replacements are hard to find. A 5 HP today isn't built like the over built ones of years past. 

I found this online a few weeks ago. Don't know if it works well but I plan to try it next time I need a new switch. 

http://www.bowl-tronics.com/Stsw.html

Can you replace the current motor with one that doesn't require a centrifugal?


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## Big John (May 23, 2010)

It doesn't sound like a bad switch, unless it's a bad batch, because he's already replaced it more than once.

If the switch is heating up and sticking it's either arcing or holding too long, both of which seem to suggest the motor not coming up to speed properly. So it sounds to me like there's something wrong with the driven load where it's installed. 

I assume you took current readings on the thing when it was rebuilt, have you ever been out to trend the starting current and time once it's installed?

-John


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## varmit (Apr 19, 2009)

Did you check the voltage drop on starting? I would suspect that that there is a high resistance connection somewhere- bad breaker, loose fuse, corroded or loose termination, almost broken wire, or something that is dropping the voltage enough to prevent the motor from accelerating. Check the voltage at the final motor connection. If this is the typical farm electrical distribution, there could be a "less than ideal" method of electrical installation and some really long runs of wire to loads. Yes, the old SO cord could be a problem, or one of several problems.


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## micromind (Aug 11, 2007)

My bet is on a lousy motor. As noted, there's a lot of cheap junk presently available these days and most likely this motor was the cheapest one that could be bought.

There's a difference between cycling the start switch a bunch of times in the shop and leaving it run for a long time out in the field. It's possible that the switch sort of 'sets in' when it's in the run position for a long time, but it'll cycle just fine for short runs. 

I'd bet this is more of a design problem than anything else, if it were me, I'd be looking in to a potential relay or a simple time delay relay to disengage the start winding.


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## Tsmil (Jul 17, 2011)

My bet is on the rotting cord. Voltage drop on start up would cause abnormally high current causing over-heating of the contacts that are failing. Change out the rotting cord as it should be replaced anyway and try again. Take voltage and current readings at the motor to be sure all is within normal limits.

Good luck


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## JRaef (Mar 23, 2009)

Big John said:


> It doesn't sound like a bad switch, unless it's a bad batch, because he's already replaced it more than once.
> 
> If the switch is heating up and sticking it's either arcing or holding too long, both of which seem to suggest the motor not coming up to speed properly. So it sounds to me like there's something wrong with the driven load where it's installed.
> 
> ...


I agree, if the switch has been REPLACED and still fails, it's something else.

You mentioned something that might be related: that when you test it in the shop it is in free air so there is more load than it would see in the field. That may not necessarilly be the case. You obviously understand that fan load has to do with air movement (kudos, because many people believe the opposite), but if it is a ducted fan in the installation and you have it in free air in the shop, the load may not be the same either. In free air, the airflow is not the same as it is if ducted, the ducting directs it better to move more air, thus more load. 

So one thing you should check at the installation is the air flow control components. If his aeration fan has a guide vane airflow control system, as most do, and the guide vane is stuck wide open or the farmer thought it would be OK to leave it wide open on start up, that may be what is leading to your centrifugal switch damage. On a single phase motor, the Start circuit is not really designed to handle full load, it's just supposed to get the rotor to 80% speed. Because of that, the centrifugal switch contacts are not expected to carry current for more than a few seconds. If it never gets to the speed point because of the load on the motor, the start circuit never switches out and the centrifugal switch burns up. I've faced this issue 3 or 4 times on dryer systems, the farmers think that having the vanes closed INCREASES the motor load, so they open them wide, which has the exact opposite effect and they don't realize it.


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## garfield (Jul 30, 2009)

I would time the start at the shop and at the bin. You could also load the bin circuit with a space heater 1 leg at a time to find a bad connection.


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## varmit (Apr 19, 2009)

My "almost broken wire", in my previous post, could be a motor winding also.


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## mbednarik (Oct 10, 2011)

I had a similar problem once. At our shop we would not ground the motor frame, just hook up the hots and try it.:whistling2: Motor had a ground fault on the start winding. Took it back to the farmer and it smoked a new start switch. Just food for thought.


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## wendon (Sep 27, 2010)

Just a couple of questions, 
What brand of motor is it?
Is it possible that the rotating mech is sticky and holding the switch in too long?
Are the contacts on the switch wired in parallel or series?
Are the points burning at all? 
A lot of the switches have a steel plate that is part of the contact that 
the switch sets against when it's open. Maybe you need to use a different brand of switch?
Have you tried doing a voltage test at the motor when it's starting to see if there's a sag in the voltage?
Presumably the correct start caps are installed?
Possibly the windings are bad if it's been overheated?
If it's a centrifugal fan, the starting torque probably is pretty high.
Have to presume there's grain in the bin when you're testing it!:laughing::laughing:

Kinda long winded but just some things I'd check.


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## subelect (Nov 25, 2007)

Friday afternoon, I had the exact same problem at another grain bin 30 miles away.
This farmer had us replace the 7.5 hp, single phase Baldor motor last year. He had not run the vane-axial fan since last spring when he cleaned out the bin. 
I got out to the bin site and he had the fan motor removed from the bin. I took the end-bell off and found the stationary start switch stuck open. It must have gotten hot enough to stick to the plastic of the switch. 
All that it took was pushing on it and it released. Re-assembled the motor and bolted it back up to the bin. Ran at 40.5 amps; max nameplate data was 46, 239 volts. The bin has two identical fans fed from the same breaker box; the other fan had no issues and was operating just fine.
So, a motor that had maybe 72 hours of total run time was having the same problems that we are seeing with an older motor. The only common items were both were single phase and both were fed with old SO cord. 
I am not sure if I need to replace the cord at both problem bins with EMT & LFMC or not. 
Not really sure if this is a smart move or just throwing parts at a problem. 
Rick


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## Big John (May 23, 2010)

What was the inrush current? What did you use to measure the current? The cord itself is not the issue, but like _varmit _said, the conductor size in the cord may be an issue, did you record a minimum voltage at the motor during startup?

Just out of curiosity have you tried swapping out the start capacitors? If you're not developing enough torque it seems like the motor would start slower. While I've never heard of a "slightly bad" starting capacitor, I don't do much work with single phase motors.

-John


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## subelect (Nov 25, 2007)

I did not measure the in-rush current, but I used my Fluke 376 to measure the running current. 
I am pretty sure that the SO was 6/3, about 13' from the brk box to the starter on the side of the fan.


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## varmit (Apr 19, 2009)

If any of the problems, listed in the previous posts, prevent a single phase motor from starting quickly, the centrifugal switch can overheat and stick or burn out.


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## wendon (Sep 27, 2010)

Most of the Baldors that size have the start caps wired parallel. I've seen a pile of those motors have start caps go bad. The rivets on the original caps burn off. They will continue to start until enough of the caps are bad that it won't start. Would be a good idea to check all the caps as if one is bad it will probably still start. Used to work on motors but have never seen one do what your saying. Maybe it's a gremlin??


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## ce2two (Oct 4, 2008)

Had pool guy come over my buddys house because the jacuzzi motor locked up,the pool guy says that be 600.00 out the door:lol:I pulled the motor spent 60.00 on bearings and 30.00 to pull and press bearings back on for a total of $90.00 ...It only needed bearings, i knew that from the start..600.00:laughing::laughing::laughing:NOT!


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## wendon (Sep 27, 2010)

ce2two said:


> Had pool guy come over my buddys house because the jacuzzi motor locked up,the pool guy says that be 600.00 out the door:lol:I pulled the motor spent 60.00 on bearings and 30.00 to pull and press bearings back on for a total of $90.00 ...It only needed bearings, i knew that from the start..600.00:laughing::laughing::laughing:NOT!


He paid you $300 dollars and took you out for dinner like a good buddy should, correct?:laughing::laughing:


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