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-   -   Start capacitor problem (http://www.diychatroom.com/f18/start-capacitor-problem-124339/)

bimfi 11-22-2011 07:48 PM

Start capacitor problem
 
I have a 1985 Hobart food mixer, model A200 (20 qt) that I recently rebuilt. The motor is a 1/2 hp inductive motor. The stator is bolted to the inside of the mixer housing and has a removable rotor that is held in place inside of the stator by two shaft bearings. It also uses a start capacitor and an "old fashioned" mechanical clutch plate assembly. This plate engages the cap connections at rest, and after it spins up, disengages the cap. It took me a long time to figure out how to connect all of the wires to get it to run.
Here is my problem. When I initially finished rebuilding it, I flipped the toggle switch on and the motor started up like a champ. Obviously, the start capacitor did it's job correctly. A couple of days later, I tried to start it and it gave a very loud humming/buzzing noise. The motor did not start at first. I shut off the power and tried again. This time it took off as it was supposed to do. A couple of more days later, I started it up and it ran with no problem, but later on that day I tried it again and it gave the same loud buzzing noise.
Now, the only way I can get it to run is to power it off, shift into 2nd gear, rotate the shaft that will in turn spin the rotor rapidly. Then with the rotor spinning, I can turn on the power and it starts running. Could it be that the capacitor is either shot, or close to it. The problem is that it was a brand new cap when I installed it. I could replace the cap with a new one, but if it also craps out, then what else could be creating this problem? I have no way of measuring the cap or even seeing the inside of the motor housing when it is running because the whole motor is enclosed in the casing while running. Such a dilemma. Any suggestion would be greatly appreciated.

Doc Holliday 11-22-2011 07:56 PM

If it is not the cap then I'd suspect the windings are worn.

carmusic 11-22-2011 08:14 PM

check for bad contact in your mechanical clutch

micromind 11-22-2011 08:33 PM

Capacitors usually work or they don't. I doubt it is the capacitor, it sounds more like a problem with the centrifugal switch. It is not engaging the start winding when the motor is at rest. This is the typical failure mode of such a switch.

They can be a real bear to fix, sometimes it's easier to forego the switch and install a potential relay. This will work only if you can get the wires out of the motor to the remotely mounted relay.

Rob

bimfi 11-23-2011 12:51 AM

I believe you are correct about the centrifugal switch. I remember the first time I started it up without the plastic disk that makes contact and it sounded exactly like that. I guess I need to look at that first and see if it is broken or damaged. Thanks, everyone for the help!

bimfi 12-02-2011 01:07 PM

Quote:

Originally Posted by micromind (Post 777264)
sometimes it's easier to forego the switch and install a potential relay. This will work only if you can get the wires out of the motor to the remotely mounted relay.

I replaced the cap with a new one just to rule that out as being the problem, and it started up with no problems. The issue is that the centrifugal switch disk ends up locking itself back from the contacts when it shuts off. I really believe that the disk is the problem. It has two slots that the clutch locks into. If I could find a disk that has no slots, I think it will work better, but maybe not. I'm really thinking about replacing the mechanical switch with a potential relay. I am not really electrically proficient, so would a potential relay replace the switch or both the switch and the capacitor? Where would I go to find more information about modifying this?

Thanks,

Paul

micromind 12-02-2011 08:46 PM

When a potential relay is used, the capacitor stays in the circuit.

The relay replaces the centrifugal switch. But it needs 3 wires, not just two. It needs to see both ends of the start winding, plus break the circuit; just like the centrifugal switch.

I've had pretty good luck using submersible pump potential relays. A motor shop would likely have them, or can get them. Just match HP and voltage.

bimfi 12-05-2011 01:25 PM

2 Attachment(s)
I decided to take your advice and modify it with a relay. Because the original mechanical clutch is pressed onto the rotor shaft, I've decided to keep it attached, but removing any moving parts that could potentially interfere. I would like to attach a wire diagram showing what I propose to modify for review by either you or someone else. All suggestions will be greatly helpful.

Thanks again!

Paul

swschrad 12-05-2011 08:07 PM

I would have bought a new centrifugal switch and kept it factory. Hobart is still around. if this is a home mixer, the parts have probably gone with KitchenAid.

bimfi 12-05-2011 08:28 PM

No, it is not a "home" mixer, though I am using it at home. It is still a small industrial appliance manufactured by Hobart. You are right, that I should keep it factory. It's just that Hobart inflates their component parts so much that it is not truly feasible for someone like myself to dish out that kind of money. Plus, I don't believe that old switching technology is as dependable as the modern types. Just my ignorant view point. I will look into it though. Thanks.

micromind 12-05-2011 10:21 PM

The diagram will work. It's not too hard to connect the wiring, but you'll need to find a spot to mount the relay.

Rob

bimfi 12-06-2011 01:12 PM

2 Attachment(s)
I'm not very knowledgeable in electricity and electronics, so bear with me. I could not find a "potential" relay that would either fit or meet the requirements, but I did find a relay from Grainger. It's an 8 pin DPDT 15a relay. It's made by Dayton (model 5YR16N) and is rated for 120vac. According to Hobart, the relay should have 2 poles and be rated under 150vac. I don't know if I purchased the right type or not. I did a continuity test with my multimeter on pins 1 and 5, then pushed in the test button which seemed to disengage the contact. If that is all it is supposed to do, then I may have the right one. I'm just concerned about when the contact is supposed to open after starting. Should I be concerned about PU voltage or DO voltage? Here are pics of the relay, if that helps.

micromind 12-06-2011 09:31 PM

This is a general-purpose relay, not a potential relay. I doubt if it'd work, maybe though. I think it'll disengage the start winding too quickly.

A potential relay has a different coil, and is more precise as to when it'll transfer its contacts.

bimfi 12-06-2011 10:42 PM

Thanks for the information. I will have to do some more research and locate one. Thanks, again!

bimfi 12-07-2011 02:26 PM

Just wanted to let you know that I've decided to put the modification on hold. First, I was having a hard time finding the right potential relay. Second, I fixed the culprit of the original problem. It was that the disk that makes contact with the switch, wasn't. This was due to it being locked back away from the contact by two slots in the disk. I filled in the slots and it works fine, now. I tested it numerous times to make sure. I do thank all of you that took the time to assist me.

Paul


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