Capacitor problems, advice please.

[t8hants]

putting the capacitors in parallel, just blew the fuse, but I do hear the motor go click as it runs down.

 

[guineafowl21]

putting the capacitors in parallel, just blew the fuse, but I do hear the motor go click as it runs down.

Extra capacitance causing more inrush current. Centrifugal switch next, then.

 

[t8hants]

Sadly again all greek to me what should I be looking for by way of a fault.. I have googled centrifugal switch to see what they look like.

Edit, I have had a look at a couple of videos on centrifugal switches, so I will try and see if I can sort that out, if not probably a new motor after Christmas.

 

[EddyCurrent]

Do you have a multimeter ?
As I mentioned earlier, before you bought the capacitors, it could be the centrifugal switch contacts or the start winding itself at fault.
Using the diagram near the bottom of the page here; Compare Split Phase Induction Motor and Capacitor Start Induction Run Motor
it is possible to test the switch and winding without breaking the motor apart.
Obviously do not energise the motor while testing and do not have the capacitor connected. Just hand turn the rotor as fast as possible by hand to see if the switch opens and then closes at rest.

 

[Chris70]

You could always measure between terminals for resistance, ie, perform a continuity check. Any terminals with zero, or near zero, ohms resistance are connected, that is, electrically speaking they will be one and the same terminal. Measuring between terminals which exhibit a high, then decreasing, resistance are not connected to each other, that is, they are the true capacitor terminals. (The reason the resistance is initially high then falls is that your ohmmeter has a battery which is effectively charging the capacitor). I hope this helps, as the wally on Festool loves to say!

 

[gmgmgm]

Definitely check the windings' resistance, which is very easy: How To Test and Check Single phase Electric Motors

If you are really pulling your hair out, consider a capacitor meter. I had a few "motor problems" a couple of years ago and bought a capacitor meter. About £30, and it tells me the uF for each capacitor and whether it's good. Very handy to have for these sorts of problems.

Once you know your windings are good, and the capacitors are good, then it's probably the mechanism to switch from start to run i.e. your centrifugal switch (or in other cases a relay e.g. potential/back-EMF).

Ultimately the wiring layout for a start/run capacitor setup is pretty universal, and there are not many factors at play.

 

[johnbs]

If you open up the terminal housing, can you see four terminals as shown in this document? Hopefully marked A and Z pairs?
John

 

[guineafowl21]

Measuring between terminals which exhibit a high, then decreasing, resistance are not connected to each other, that is, they are the true capacitor terminals. (The reason the resistance is initially high then falls is that your ohmmeter has a battery which is effectively charging the capacitor).

It’s actually the other way around - measuring a capacitor on resistance setting gives a low reading that rises. We’ve hopefully eliminated the cap as a problem.

Sadly again all greek to me what should I be looking for by way of a fault.. I have googled centrifugal switch to see what they look like.

Edit, I have had a look at a couple of videos on centrifugal switches, so I will try and see if I can sort that out, if not probably a new motor after Christmas.

You’ll have to open the motor up. On the rotor (spinning part) there should be an obvious switch with a spring and flyweights to pull it in and out of contact. The contacts might need a clean, or there may be a wire off. Take some pics!

 

[t8hants]

I have put my multi meter set at 200 ohms on the original capacitor and the new one. The original capacitor reading starts at 1 and counts down to 0.002 where it stops, as does the new capacitor when the terminals are paired in one way and remains static when connected the other way.
Am I right in thinking the old capacitor is actually functioning as it seems to behave the same as the new one?

 

[guineafowl21]

I have put my multi meter set at 200 ohms on the original capacitor and the new one. The original capacitor reading starts at 1 and counts down to 0.002 where it stops, as does the new capacitor when the terminals are paired in one way and remains static when connected the other way.
Am I right in thinking the old capacitor is actually functioning as it seems to behave the same as the new one?

Forgive me, because I don’t know your experience with multimeters, but that doesn’t sound like you’re reading it right.

The 200 ohm range wouldn’t read down to 0.002 (that is 2 milliohms*), and the scale would count up, not down on a new capacitor. If you quickly switch the probes, the reading would go negative, up to 0, then rise to over limit (“0L”, or sometimes “1.”)

Given your description of the original cap as ‘ancient’, I thought it best to eliminate that as a cause by replacing it. It’s possible the old cap has drifted up or down in value, or varies with temperature, or many other things. You really need a capacitance meter and leakage tester to check.

*An implausible level of precision for that range. And the meter leads alone would have a resistance of at least a hundred times that.

 

[Phil Pascoe]

While you knowledgeable people are here, what do I do with this one? I'm fairly sure it's the capacitor that's the problem but I don't want to wreck this one if it's not. The innards are reluctant to come out so I can't see the terminals. Would a replacement be pre wired? There are only two wires (cores) from it.

 

[guineafowl21]

While you knowledgeable people are here, what do I do with this one? I'm fairly sure it's the capacitor that's the problem but I don't want to wreck this one if it's not. The innards are reluctant to come out so I can't see the terminals. Would a replacement be pre wired? There are only two wires (cores) from it.
View attachment 97270

That looks like quite a low value (16uF) - are you sure it’s not a run cap? Easiest thing is to replace it, as they are cheap compared to the overall machine. They usually come with spade terminals, so if your cap is hard-wired (which is a bit silly), then you’ll need to cut the wires and crimp some on.

Main ratings to follow are 450Vac and 16uF, motor start/run cap.

 

[t8hants]

My experience with multi meters is shall we say basic, but attached are the photos taken of a repeated connection of the old capacitor. 1 being with it on and unconnected 001 being the value with the thing connected to the capacitor, swapping leads or terminals makes no difference to the indicated value.

 

[Racers]

Is it a 4 terminal cap? Because it sounds like you are measuring the internally connected terminals giving you the low resistance reading.

Pete

 

[guineafowl21]

My experience with multi meters is shall we say basic, but attached are the photos taken of a repeated connection of the old capacitor. 1 being with it on and unconnected 001 being the value with the thing connected to the capacitor, swapping leads or terminals makes no difference to the indicated value.

Ok, it’s on the 2000 ohm range. The left picture is reading over limit, ie open circuit. The right-hand picture suggests 1 ohm. If this is the true, stable reading, your capacitor is reading as a 1 ohm resistor, and if so, can be considered short circuit.

I assume the cap is disconnected from the motor, in which case either the cap is dead or your meter is.

 

[guineafowl21]

Is it a 4 terminal cap? Because it sounds like you are measuring the internally connected terminals giving you the low resistance reading.

Pete

Cross post - good point!

With all due respect to the OP, this is why remote diagnosis is so hard, and why I suggested just replacing the cap.

@t8hants I sense you’re reluctant to open the motor up. Do you want us to explain how to test the centrifugal switch without doing so?

 

[t8hants]

The old capacitor is a two terminal with the readings pictured (it was disconnected from the motor). The new capacitor is a four terminal version, connected to the multi multi-meter one way it remains static on 1, connected the other way the m-m behaves exactly the same way as the old capacitor, no settings were changed.

 

[guineafowl21]

The old capacitor is a two terminal with the readings pictured (it was disconnected from the motor). The new capacitor is a four terminal version, connected to the multi multi-meter one way it remains static on 1, connected the other way the m-m behaves exactly the same way as the old capacitor, no settings were changed.

For the new cap, do you mean [_001] on the display, or [1___]?

 

[t8hants]

The meter starts at 1 when switch on, and will drop down to 001 when connected to the new capacitor, as per photos, the new and old capacitors give the same result.

 

[guineafowl21]

The meter starts at 1 when switch on, and will drop down to 001 when connected to the new capacitor, as per photos, the new and old capacitors give the same result.

An earlier post suggested [1___] one way and [_001] the other on the new cap. You should make sure the new cap is connected using the terminals that give a stable [1___] reading.

[1___] is a normal reading for a capacitor, but it won’t tell you good or bad. A good meter will spot the count up, but yours must have a very slow refresh rate. You will also see [1___] on a knackered cap with some capacitance left. You are performing an inadequate test, with a cheap meter, and without the knowledge to interpret it. I rather wish we hadn’t gone down that road at all.

Please stop fiddling with the new cap and address the next stage in the diagnosis, which others have been pushing you towards. Do you want to:

A) Test the centrifugal switch electrically
B) Open up the motor and inspect everything directly.

My suspicion is that you’ll need to do B anyway.