I fear this might be a little bit too simple for this Stack but I'll still ask. I dismantled a motor from an electric meat slicer of the very old type:

old meat slicer motor

When I opened the enclosure I found that the top part (the opposite of the wired side) could be taken off and on the inside of that enclosure lid there is some sort of electric wired spring mechanism. The wires of the spring where already loose when I took it off, so I don't even know where those cables went:

enclosure top lid with spring

My question really is this: Can I safely fire up the motor without wiring back on the spring? What does this spring do? How would I wire it back on?

Follow up

According to the answer of Dave Tweed I took a closer look and there are two almost opposite loose wires on the stator. They do rather look like broken than seperate wiring though (there's a third one which is loose but not open ended). Also I cannot make out any kind of capacitor without further disarming this, which is beyond my skills.

loose wires on stator

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    \$\begingroup\$ Could it be a brake? Can you turn the shaft when the motor is not connected to anything? \$\endgroup\$ – Dutch2 Nov 15 '17 at 17:04
  • \$\begingroup\$ Yes I can, quite smoothly actually. \$\endgroup\$ – Marian Nov 15 '17 at 17:08
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    \$\begingroup\$ @Marian frankly, you didn't provide the IMVHO most important information - what are the voltage/current/power specs of the engine, and how experienced are you with power electrics? If it's powered by any voltage higher than 24V, sucks more than 100W of juice, and especially if it's powered by mains voltage and is in kW range, without real EE experience you're actually risking your life if you power it on... or when you power it off. (cont) \$\endgroup\$ – vaxquis Nov 16 '17 at 4:34
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    \$\begingroup\$ I'm speaking from both my own experience and common knowledge. Bear in mind that inductive elements generate huge spikes of current on power-off (i.e. inductive kickback), and the capacitors that are used to smooth the voltage, shift phases and filter the EMI, if used with mains voltage, can store enough power to at least burn and/or kill a person. I've had a dozen of accidents with damaged LC circuits, and can assure you of one thing - they hit you when you least expect it; because they store the power, turning the machine off doesn't make it any safer. \$\endgroup\$ – vaxquis Nov 16 '17 at 4:37
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    \$\begingroup\$ tl;dr I wouldn't recommend repairing damaged/improperly disassembled/assembled engines/transformers/PSUs etc. to laymen, if they don't have an exact death wish. \$\endgroup\$ – vaxquis Nov 16 '17 at 4:44

If there is no capacitor or evidence of there having been one, then what you have is an older technology called a "Split Phase" motor, a type of single phase motor design that was used eons ago, before capacitor-start motors were cheap and easy to build. Their down side was very low starting torque, which on something like a meat slicer, would likely have not been a problem. But that lack of starting torque was problematic for a lot of other machinery, so their use fell out of favor once cap start motors came along.

In that motor design, the centrifugal switch was absolutely necessary; the motor will fail to accelerate without it. Here is what the internal wiring looks like: enter image description here

At rest, the Centrifugal Switch is closed and when power is applied, it goes to both the Start winding and the Main winding. The phase shift in between the two winding creates the relative rotational difference that makes it start to spin. then once it gets to about 80% speed, the centrifugal switch opens up and the motor runs on only the main winding, because once spinning, a single phase motor will keep spinning. but without that initial phase shift, the motor just sits there and hums because there is no rotating magnetic field, it just vibrates back and forth 120 times per second.

My suggestion is to take it to a motor shop and have them test the windings, clean it thoroughly, test the connections and re-assemble it. They will know what to do, even though you don't know where those wires came from.

  • \$\begingroup\$ Lovely. Well explained, informative and spot on! \$\endgroup\$ – Marian Nov 18 '17 at 17:12

The spring mechanism appears to be part of a centrifugal switch arrangement, which would be crucial to getting the motor started. Trying to start the motor without it would result in no rotation and excessive current draw.

  • \$\begingroup\$ Would you have an idea of where the wires should go? \$\endgroup\$ – Marian Nov 15 '17 at 17:11
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    \$\begingroup\$ Normally, there would be a second winding on the stator, along with a capacitor of some sort to shift the phase. The centrifugal switch connects this winding to the mains when the motor is stopped, and disconnects it when it gets up to speed. \$\endgroup\$ – Dave Tweed Nov 15 '17 at 17:13
  • \$\begingroup\$ I had a closer look and found two loose open ended wires (see edited post). Would I wire those together? Could I break the motor if I did and it wasn't the purposed scheme? \$\endgroup\$ – Marian Nov 15 '17 at 17:43
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    \$\begingroup\$ There is nothing useful you can do without the correct capacitor. Determining what that would be would require quite a bit of analysis of the motor at a level that you don't seem to be equipped to handle. \$\endgroup\$ – Dave Tweed Nov 15 '17 at 17:47

It is possible that the leads marked are supposed to be connected to the centrifugal switch, but they also could be broken wires from a burned winding. One of the groups of windings is much darker than the other I suspect that is a sign of failure. It is possible that only the winding starts the motor without a capacitor. Some induction motors are designed that way. Starting the motor depends on the difference between the reactance.resistance rations for the two windings. It is not clear to me how the coil spring shown is supposed to be installed. Only someone with a reasonable amount of experience should attempt to do anything with this. It is doubtful if it is worth anyone's time to fool with it. It looks like scrap to me.

  • \$\begingroup\$ Thank you for your valuable opinion. I actually disarmed the rotor from the stator, which I first thought I wouldn't be able to and there really is no capacitor anywhere. I tried to wire the mentioned leads in different ways without any success. I suppose I'll stop here and ask a local shop for their opinion. I'm in a small town, if it has repair it's still worth it over buying a new motor. \$\endgroup\$ – Marian Nov 15 '17 at 19:09
  • \$\begingroup\$ It there was a capacitor it would be external. It would be under a cover screwed to the side of the motor housing or inside the housing of the driven machine. \$\endgroup\$ – Charles Cowie Nov 15 '17 at 19:13

It's difficult to be certain from the images you supplied, however the assembly with the spring inside the end cover that has been removed looks like it could be the centrifugal (stationary) start switch. You can probably confirm that it is a spring-loaded switch by applying pressure on it at the point where the shaft passes through it. If it responds with a "click" action then it is definitely a switch, and/or you could confirm by checking for continuity across those wires.

The assembly protruding from the shaft with the spring looks like it is the centrifugal weight that activates the switch, although again it's difficult to see how it operates. If you "lift" that disc away from the shaft (i.e. to compress the spring) and that causes the disc sitting on the shaft to move towards the end of the shaft (i.e. towards the switch in the end cover) then that would confirm that it is the centrifugal switch start mechanism.

If that's not the case then another possibility is if the shaft moves axially when the motor is assembled (i.e. if you can push the shaft in) to activate the switch then it would appear that the motor is designed to run only when pressure is applied to the end of the shaft. In that case I would assume that the machine has a mechanism to press the shaft in when the operator applies pressure to some part of the machine, either as a convenience to the operator or as a safety feature (and perhaps both).

Checking the continuity between those wires should also give confirmation of what it is. If there is continuity which is broken when pressure is applied then it is a "start" (centrifugal/stationary) switch. If it is open but gets continuity when pressure is applied then it is an operation/safety switch.

To answer your question:- no it's not likely that you would be able to run the motor without re-connecting those broken wires. If the switch is part of the starting mechanism, then best case is that you may be able to manually spin the shaft to get it moving before applying power (I wouldn't risk doing it after power is applied), assuming that the shaft spins freely enough to keep rotating long enough for you to then get power to it. That would only serve to see if the motor otherwise still operates, of course, since it still needs to be repaired before you can fit it back into the machine. If it turns out to be an operation/safety switch then of course it will need to be reconnected and also pressure applied to the shaft (I wouldn't risk trying to do that with the motor connected to power).

If you do decide to attempt a repair, pay careful attention to where those wires end up as you reassemble the motor as they will have to stay clear of that assembly on the shaft which will of course be rotating when the motor operates.

  • \$\begingroup\$ Thank you for a very informative and inspiring answer on the topic without rants, I highly appreciate it. I am not further attempting to repair this on my own but every comment is a great step towards maybe getting it done in a local shop. I'll definitely check for continuity as you mentioned. I'm not right now on it, but yes I do remember that the shaft could be pushed slightly in and out. Thanks again for a very informative comment! \$\endgroup\$ – Marian Nov 16 '17 at 18:27

I suggest You not to! The top part (lid) keeps the shaft centered and in place.

edit: After editting your question it now makes more sense. So You could absolutely try, but it might be some sort of countermeasure to start the motor without the lid on. Not hooking up the wires to their original places may result in no movement at all.

I would give it a go.

  • \$\begingroup\$ Sorry I guess I wasn't specific about this. I really refer to the spring mechanism and it's wiring. The idea would be to put the lid on but not wire those cables because I really have no idea where they would go. I edited my question to reflect this better. \$\endgroup\$ – Marian Nov 15 '17 at 16:55
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    \$\begingroup\$ @Marian I have edited my answer as well. \$\endgroup\$ – Zoszko Nov 15 '17 at 17:01

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