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Capacitor problems, advice please.

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Pete Maddex

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A few microfarad capacitor probably won’t give much so a reading when testing with a digital multimeter try connecting the way you get no readingi and then reversing the connections, and try the diode setting next to the 200 ohm setting.

Pete
 

t8hants

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quite happy to put the capacitors to one side, but I only get a reading of 1 when the meter is on, but disconnected from the capacitor, the moment it is connect that is when the reading will drop to 001. I do not get a stable 1 with the meter connected to the capacitor.
With the circuit diagram of the centrifugal switch, I remain unclear to which terminals on the motor to connect the meter.
 

guineafowl21

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The new capacitor is a four terminal version, connected to the multi multi-meter one way it remains static on 1,
I do not get a stable 1 with the meter connected to the capacitor.
This is why I’m confused.

The [1___] means over limit (open circuit) and is nothing to do with the number 1.

With the motor unplugged, remove the capacitor and probe the two resulting connections with your meter set to 200 ohm range. Tell us the reading. Be sure to differentiate [1___] from [_001].
 

EddyCurrent

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Referring to the diagram, I'm assuming your motor is similar.

The capacitor normally connects to D and A
The mains supply to the motor normally connects to B and C

With the motor disconnected from the mains and the capacitor removed;
Testing the start winding.
1.Connect the meter to C and D and measure the resistance (Ohms)

Testing the centrifugal switch
2. Now connect the meter to B and A and measure the resistance, it should be zero ohms or very very close.
3. With the meter still connected to B and A, spin the motor as fast as possible by hand and the reading should go to infinity then back to zero when you stop spinning it.
 

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johnbs

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I'm desperate to see this resolved! Please OP, could you post a photo of the new cap's terminals?
Then set multimeter on 200 ohm range. When you have the new cap's terminals correct, you should get the following pattern:
Meter not connected: overflow = 1___​
Meter connected: starts low and rapidly increasing reading until terminating in overflow again​
Meter REVERSED: ditto but will take longer to overflow. *​
This assumes the new cap is not faulty and you've got the right terminals, which is not an unreasonable assumption.
You don't need to dismantle the motor to establish if the centrifrugal switch is OK. Look at the photo I posted, if you have four terminals , use the meter on 200 ohms again to check continuity A1 to Z1 or equivalent .
John
* reason I've added this step is if the cap has charged to the multimeter's maximum sense voltage, you will get an overflow immediately when connecting the meter. Reversing the meter means you guarantee that the cap has to be charged by the contant current which the meter puts out (probably 1 or 10mA on 200 ohm range)
 

t8hants

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I will try and do that tomorrow John, the wife has had a few days off, so I have been out of the workshop doing the larger chores for her.
 

t8hants

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I have taken the series of photos requested. I have discovered that for my first set of readings posted above I had the meter set at 2000, not 200 ohms, my bad!!

Photo 1 is the setup unconnected and reads 1,
Photo 2 is a connection across the plastic ridge and the reading remains unchanged at 1, the same result is given if the terminals are connected diagonally across the ridge and remains at 1.
Photo 3 is a connection on the left hand pair of terminals and gives a reading of 1.9, and it appeared to be stable.
Photo 4 is the right hand pair of terminals connected and they gave a stable reading of 1.3.
Photo 5 shows the old 'tin can' capacitor and it reads 1.9.

I hope that clarifies the mud.
Gareth
 

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guineafowl21

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Your old cap is shorted.

The new cap is behaving normally, but only when connected correctly, ie across the bridge (as in P2.jpg). The terminals are linked internally, paired L and R as you have labelled.

If you connected the new cap as per P4 or P5, it would not have worked.
 

t8hants

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I have connected the capacitor correctly with the result the motor now runs at full speed clockwise, but only if kicked off by hand.
As it slows to a stop, there is a distinct 'click' and the shaft gives a slight twitch.
Several start attempts produced the same result, so I presume I must now look at the centrifugal switch?
Which end will it be under, the wiring board or the pulley end please?
Sorry to be a PITA.
Gareth
 

Ttrees

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This is a very interesting thread
I can't advise anything, but will mention tape or draw a line down the motor so the end bells will realign again.
it could be trickier otherwise if they are a tight fit.
 

guineafowl21

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Sorry to be a PITA.
You’re not! You just got a bit hung up on testing the capacitors on resistance mode, which is interesting but not very useful.
Which end will it be under, the wiring board or the pulley end please?
If you follow @EddyCurrent ’s post #44 you can test as per his diagram, with the meter on 200 ohm range.

If you want to dismantle, the switch is usually on the back end, ie not the pulley end. Good advice from @Ttrees to draw a line along the motor.
 

t8hants

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Just to help things along I have taken a photo of the wiring connections as found on my motor ( I didn't wire it up myself), but this is just to check the motor is wired up correctly. Cables I name as 'motor cable' simply come from inside the motor and AC as from the 13amp plug.
Starting from left to right and numbering in that order
Post 1 has the AC negative wire, a connection to the capacitor, and the long red motor cable seen in the photo.
Post 2 has two motor cables coloured black and red
Post 3 has the other capacitor connection, and the AC positive
Post 4 has the AC Earth cable.
It is also possible that the AC Negative cable was shorting on post 2, bare wiring was very close to the terminal.

Motor connections.JPG
 

guineafowl21

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If what you say is correct, your cap is wired across the mains. This is not correct and you should really start again with the wiring. At this point I strongly recommend you take it to a motor shop or electrician. It’s possible a change of cap connections would get you going, or we could guide you through identifying the motor connections and rewiring, but it would be somewhat painstaking. A motor in this state should also be meggered for electrical safety.

Sorry, I had assumed the motor was working, then stopped, so the wiring was most likely correct.

Please reconfirm the connections, because if your old cap was shorted and across the mains, it should have just popped the fuse.
 
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t8hants

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Sorry, I had assumed the motor was working, then stopped, so the wiring was most likely correct.
Unfortunately I can't remember the history of the motor, I may well have inherited from my father the better part of 25 years ago and along with with several others, it just sat waiting for the day it would become useful.
The wiring looks very unimpressive and will need to be neatened up, if the motor is Ok.
As stated with the new capacitor the motor will run nicely, if started by hand. I was also hoping for guidance on which of the terminals to use in doing the test as mentioned above, before i delve into its internals.
 

guineafowl21

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Sorry, I had assumed the motor was working, then stopped, so the wiring was most likely correct.
Unfortunately I can't remember the history of the motor, I may well have inherited from my father the better part of 25 years ago and along with with several others, it just sat waiting for the day it would become useful.
The wiring looks very unimpressive and will need to be neatened up, if the motor is Ok.
As stated with the new capacitor the motor will run nicely, if started by hand. I was also hoping for guidance on which of the terminals to use in doing the test as mentioned above, before i delve into its internals.
If you’re determined, then I’m happy to help, but it might not be easy.

Would you mind reconfirming the connections? For example, I think I can see a wire going into the motor from post 3, which is not mentioned. Also, as I say, it should have popped the fuse with the old cap if connected as per your description. Pull the capacitor wire down so we can see what’s going on.

Ideally, draw a diagram of the connections and take a photo.

Also note, there is no such thing as AC positive and negative. It’s live (or line) and neutral.
 

t8hants

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Well spotted, I took stronger glasses and there is indeed a black motor wire attached to post 3, which is exactly how it was marked originally, as I cleaned the white smudge alongside it, so the posts appear to be originally marked 1,2,3.
I have attached a wiring diagram as it appears to me, apart from the live and negative cables which are colour striped, the colours are correct.
As I don't know where the 'motor' wires connect to I have just marked them as such.
I have no desire to delve into the motors internals unless it cannot be avoided.

BTW thank you for taking the trouble to help.
Wiring.JPG
 

guineafowl21

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It looks like the incoming neutral should go to post 2.

Before you do this:
1. Make sure it’s unplugged.
2. Disconnect the capacitor.
3. Measure resistance, on 200 ohm range, between posts 1-2,1-3, and 2-3.
 

t8hants

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I have, I hope followed your instructions correctly and taken have the measurements, with the wiring unchanged.
We have readings of, although they all fluctuated slightly.
1-2 = 26.8, 1-3 = 32.9, & 2-3 = 7.1 .
I took pictures of all three set ups to confirm I did the test correctly.
 

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guineafowl21

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That fits with the sketch I’ve made below. You might notice that the first and last readings sum up to the middle one. You were measuring the start winding, then both, then the run winding (I hope).

Again, with the motor unplugged, reconnect the capacitor, then move the neutral connection from post 1 to post 2. Put on a new crimp connector if you have one. If not, maybe just strip the wire and clamp it under the nut.

With the motor steadied somehow, plug in and switch on, being ready to switch off again quickly. If all goes well, it should run.

image.jpg
 

t8hants

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Success, the motor starts and spins!! I owe a big thank-you to the help I got on here, but especially to Guineafowl21, for taking me through the diagnostic process stage by stage.
Now I can marry it to my saved from scrap Myford ML8 and enter the wonderful ( I hope) world of wood turning, although I am slightly hampered by my dear wife who doesn't like turned objects that much, Oh well. Still once again thank-you one and all.
Gareth
 
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