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Problem with electric motor

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Graham Titman08/01/2016 18:55:46
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132 forum posts
18 photos

Hi i have recently bought point.3kw electric motor it will sit there buzzing but will not run unless you spin it with your finger and will then go in either direction.I was told it was working when it was removed for a 3phase conversion.I hope to use it to power a small tool and cutter grinder and wonder if it needs a start capacitor so i can use it with a nvr switch. Unfortunately i cannot get a photos to upload to a album at the moment.

Martin Connelly08/01/2016 19:08:51
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2137 forum posts
222 photos

There is probably a start capacitor, a start coil and a centrifugal switch to switch the start circuit off when the motor is up to speed. Two possible problems that can occur with motors left in storage for a time is the capacitor degrading for some reason but possibly more likely is the centrifugal switch jamming. This is a mechanical operation and dust and grease can jam it up. It is often possible to hear a click as the switch makes contact after power is switched off when the motor is spinning down. Since you can get the motor to run I suggest running it then turning off the power and listening for this click as the motor slows. If you hear nothing then the next step is to open up the motor casing (with power disconnected) and seeing if the switch is jamming and can be cleaned and put back into use.

Martin

Edited By Martin Connelly on 08/01/2016 19:09:55

Emgee08/01/2016 20:27:37
2426 forum posts
290 photos

Hi Graham

Can you post the details off the motor plate ? are you sure it's not 1/3 HP as 1/3 kW sounds unusual.

Some small motors are just induction motors and need a capacitor in circuit to start and run, not all have the centrifugal switch referred to, Parvalux are induction without any switch.

Emgee

bodge08/01/2016 21:07:07
186 forum posts
3 photos

The clue here is , the motor runs in whatever direction you spin the shaft ! If the shaft spins really freely it should run without having to spin it by hand and only a second or two of buzzing, but the direction it runs will be pot luck, Due to the position the rotor stopped at when last came to rest . I have a motor 1/4 hp 1428 rpm does the same thing, set it going which ever way you want by giving a spin by hand then turn the power on. Its never had capacitor fitted, there is a centrifugal switch inside and the way this is configured with the start windings makes it a run either way motor. It makes sense that ones meant to spin by hand. how else are you going to get it going in direction you want ! Yes you can use a nvr switch and i dont think there is any thing wrong with your motor, the motor i have is at least 90 years old .

b.    that is much younger than the one i have !

Edited By bodge on 08/01/2016 21:14:01

Graham Titman08/01/2016 21:07:09
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132 forum posts
18 photos

Hi i hope i have just loaded two photos to a album,there should be one of the plate and another of the wiring in the connecting box. Martin i have just run the motor when i switched on it just buzzed and when i twisted the shaft either way it just run silently with a very slight hum.Graham

bodge08/01/2016 21:36:00
186 forum posts
3 photos

very slight hum.Graham

Sounds like all is well then. Nice motor, run either way motors are maybe a bit rare, yours is the only other one i have heard of.

b.   best to spin motor shaft first then quickly switch power on, gives the start winding a bit easier time of it

Edited By bodge on 08/01/2016 21:43:20

Ian Parkin08/01/2016 21:39:57
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1021 forum posts
239 photos

Have you removed a capacitor?

your rating plate shows the specification needed

looks like it may be connected to your 2 spare connections on the terminal block

Andy Holdaway08/01/2016 21:42:13
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167 forum posts
15 photos

Looking at your photo of the terminal box, Z2 appears to be not connected. This is the end of the start winding and should have a start capacitor connected between Z2 and neutral.

wheeltapper08/01/2016 21:48:21
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424 forum posts
98 photos

+1 for fitting a start capacitor.

spinning a motor to start it is a good way to lose a finger!

Roy.

Emgee08/01/2016 21:56:40
2426 forum posts
290 photos

Agree with Andrew and if it goes the wrong direction change those 2 wires around.

Try a 6uf 400volt motor rated type to start with, should be enough to kick it away.

Emgee

Edited By Emgee on 08/01/2016 22:26:45

bodge08/01/2016 22:08:13
186 forum posts
3 photos

 

spinning a motor to start it is a good way to lose a finger!

Not if you spin the shaft first then turn the power on! Also its a run either way motor!!

So how else are you going get the right direction, keep turning it on and off till it comes right! if the start windings will stand it?

b.

run either way ,as in you dont need a reversing switch.

Edited By bodge on 08/01/2016 22:34:54

Bruce Edney08/01/2016 23:18:11
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164 forum posts
53 photos

Pretty sure that rating plate indicates a 10uF 400v capacitor

John Haine08/01/2016 23:29:28
4679 forum posts
273 photos

Yup. Capacitor start and run motor. Once fitted motor will start and run only one way.

bodge08/01/2016 23:48:46
186 forum posts
3 photos

Pretty sure that rating plate indicates a 10uF 400v capacitor

Bruce

i think it reads that way too, it maybe the capacitor is internal, i have a 1/2hp compton/parkinson with internal start cap. But op says run either way, so one still has to give a spin to get required direction

b.

probably why he thinking of using it t/c grinder. the motor i have, the contacts & c/f switch are configured different to the other motors i have and no amount of capacitors are going to make any difference to which way it runs, its either pot luck or spin it the way you want it go

b.

Edited By bodge on 09/01/2016 00:02:45

Edited By bodge on 09/01/2016 00:31:33

John Haine09/01/2016 07:28:06
4679 forum posts
273 photos

It's obvious that there isn't an internal capacitor, the motor is almost certainly cap start and run, you can see the ends of both windings in the connection box. I have a rather similar parvalux motor with an external capacitor which is wired in series, there's a neat little wiring trick that gives you reverse switching with a one pole changeover switch. Once the capacitor is wired in it "tells" the motor which way to run through the relative phase relationship. It's got nothing to do with where the motor came to rest. As the OP says it was removed from a machine and the capacitor was probably left behind. Just buy yourself a capacitor, they are easily available, problem will be solved. If this had a start switch you would hear it engage as the motor slows to a stop after running.

Les Jones 109/01/2016 08:53:03
2257 forum posts
156 photos

I agree with the comments that the start capacitor is missing, As the motor information plate gives the rating of the capacitor I think you should get the right one (Unless you have one in stock between 6 an d 15 uF It must be at least 400 volts AC rating.) If the motor runs in the wrong directon swap over the Z1 and Z2 wires. This is one source on ebay   This wire ended one would be better as you would not need to mount it in a box.

Les.

Edited By Les Jones 1 on 09/01/2016 09:01:19

John Haine09/01/2016 09:51:15
4679 forum posts
273 photos

Yup, just the job Les. I'll post the wiring diagram with a reversing switch.

John Haine09/01/2016 10:56:05
4679 forum posts
273 photos

Here is the circuit. W1 and W2 are the windings. One end of each is commoned, the capacitor is connected between the others, and the changeover switch applies live to one end or other of the cap. To ensure the motor runs in opposite directions both windings need to have the same sense, I.e. Common the wires of the same colour. You need a separate zero volts on off switch in circuit too.

image.jpeg

Emgee09/01/2016 12:54:40
2426 forum posts
290 photos

I agree the drawing John has provided suits a 3 wire motor such as a Parvalux but the OP motor has the ends of both windings in the connection box, this makes me believe it is possible only the start winding requires a capacitor. The resistance will be different on each winding if this is the case so is easily checked with a multimeter.

If windings are identical resistance then use a 240v10A SPDT centre Off toggle switch to fit as John's drawing, the live to the centre pins and the windings/capacitor on the outside pins, this type of switch will provide fwd/off/rev for your tool grinder.

Emgee

Les Jones 109/01/2016 13:01:26
2257 forum posts
156 photos

I agree with Emgee's comments that this simple reversing method is only suitable for motors with IDENTICAL windings and no centrifugal switch. If the OP needs the motor to be reversible we can give him a diagram of how to do it.

Les.

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