Help please- Creusen grinder humms but won’t spin

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--Tom--

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Picked up a second hand creusen bench grinder.
Apparently left the seller working fine, but on arrival and plugging it in it just humms

The switch seems to work - the contactor stays in when it’s powered and not when it isn’t.

Thought it might be the capacitor so ordered a spare with the same rating but swapping it out didn’t change anything and it just humms when powered up.

Original on left and new on the right

IMG_1265.jpeg


Any ideas before I call it quits and send it back?
 
Crusen had a period where the switches were pants. If you have a multimeter check it’s connecting. If that’s fine, check the capacitor is wired correctly to the motor, if someone’s been meddling beforehand they can have messed where it’s wired in.
 
Seller has refunded which is great, also said no need to return as they’ll just bin it. So keen to carry on trying to get it going.
With capacitor ruled out (moved the one that it came with to another grinder and that started up fine) is it now likely to be the switch?

Guess it’s worth ordering a new one on Amazon to check (Amazon for easy returns if no joy)
 
An AC motor requires phases that are out of sync to spin. Without this the AC just makes the motor bounce back and forth, hum, at the uk electric frequency. The capacitor causes a phase offset as the rate it charges and discharges is slow compared to the frequency of the uk grid.

The motor internally has a set of coils that take a feed, some from the supply and some from the capacitor. If the motor is humming then it is getting some power. The next steps for me would be trying to trace the wiring and ensure everything is connected to the phases in the motor correctly.

As others have said one test is when the motor is humming to spin it by hand, once moving it should stay spinning. There is obviously risk in this and beware to make sure you don’t end up attached to the spinning motor. One way to spin it up is to wrap a rope/belt around the wheel then pull it like a lawnmower starting rope. Once its spinning turn it on.
 
As others have advised - this sounds like a failed start capacitor but having swapped that one might suspect a wiring or contactor issue.
I have a Creusen low speed grinder however I don't think it has a contactor start - just a simple on-off switch.
Am out this morning but will take a closer look later to see if it will assist.
 
I have one that I will be selling , Let me know if you are interested and I will list it in the for sale section.
With photos and a short video of it running.
 
An AC motor requires phases that are out of sync to spin. Without this the AC just makes the motor bounce back and forth, hum, at the uk electric frequency. The capacitor causes a phase offset as the rate it charges and discharges is slow compared to the frequency of the uk grid.

The motor internally has a set of coils that take a feed, some from the supply and some from the capacitor. If the motor is humming then it is getting some power. The next steps for me would be trying to trace the wiring and ensure everything is connected to the phases in the motor correctly.

As others have said one test is when the motor is humming to spin it by hand, once moving it should stay spinning. There is obviously risk in this and beware to make sure you don’t end up attached to the spinning motor. One way to spin it up is to wrap a rope/belt around the wheel then pull it like a lawnmower starting rope. Once its spinning turn it on.
Cheers - now I don’t have much to lose will take the whole thing apart and try to trouble shoot everything.

I tried manually spinning to try getting it going but no joy.

Switch is a Kedu JD3 and a found a vid online of taking one apart to check it over.

Just returned friends multimeter I borrowed so will add one to the shopping list.
 
You could always try swapping any two of the phase connections. Doesn't matter which ones. Just to make sure they're out of sync. Don't think I've seen a 3 phase motor with a start capacitor though, normally they don't need them because the out if phase phases on the coils provide the force to start it up. Is there a built in inverter?
 
This is all a bit of a puzzle! The relatively low capacitance (5 microFarads) indicates it's a run capacitor rather than a start capacitor (which tend to be 100 to 1600 µF. The switch does seem to be a three-phase one however, and as Ronniel says above, it's not at all normal for a three-phase motor to have one.

But maybe it's there so a three-phase motor can be run from a single-phase supply - see for example https://engx.theiet.org/f/discussio...-three-phase-motor-from-a-single-phase-supply

interested to know how you get on - good luck!
 
This is all a bit of a puzzle! The relatively low capacitance (5 microFarads) indicates it's a run capacitor rather than a start capacitor (which tend to be 100 to 1600 µF. The switch does seem to be a three-phase one however, and as Ronniel says above, it's not at all normal for a three-phase motor to have one.

But maybe it's there so a three-phase motor can be run from a single-phase supply - see for example https://engx.theiet.org/f/discussio...-three-phase-motor-from-a-single-phase-supply

interested to know how you get on - good luck!
You can run a 3 phase motor directly off a single phase but it's really inefficient and has much reduced capacity, seems unlikely they would do this in this case. To do it properly needs a VFD.
 
Did I miss something....?!? 🤔
At what point in this thread did @Tom say that it was a 3 phase machine...?

The switch clearly shows it is 230v single phase and the fact that it's a small motor & got a capacitor speaks volumes on it's own...!
 
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I used to have a red Creusen grinder, which I think is the same as the grey professional units. It was single phase and just had a switch rather than a starter which this machine has. A quick google for a circuit diagram does indeed show that the 3phase machines have a 240v coil in the contactor so run of neutral (weird!)
Anyway, what does the label plate on the outside of the machine say, as that doesn’t appear to be a starter cap. It looks like someone with knowledge has created a phase to run a 3phase motor or single phase.
 
The red creusen have two leads going to the motor from the switch and two to the cap. The grey have 3 running from the motor to the switch with it not just being a simple switch.

It is marked up as single phase (or I’d not have bought - still have a very nice 3ph Arboga drill in bits trying to work out how to get it running off a vfd)

It feels fixable - thanks for all the ideas! Wife is off on holiday with friends next week so I’ll have plenty of evenings in the workshop coming up.
 
Here’s a rough diagram of how your, presumably, permanent-cap motor is configured.
image.jpg
With the cap disconnected, you can see how measuring resistance between L and N (L/N in the diagram as we don’t know which way round they are) will give you the resistance of the main winding M.

You now have to use some logic to find the main winding end NOT connected to the cap (X) and the cap terminal NOT connected to the main winding (Y). This will give you the resistance of the start, or auxiliary winding A. It should be higher than the main*.

Hopefully, the manufacturer has been kind and made the main winding wires the same colour, and different from the aux ones.


* Or, for an easier test, disconnect cap and measure between motor L and N, then measure where the cap was connected. If the first reading is open circuit, main winding is goosed. If the second reading is open circuit, your start winding is goosed. I don’t have to remind you to do all this with the motor unplugged, do I?

Also, beware of getting a zap from the cap terminals, since with an open winding it won’t be able to discharge.
 
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