trying to understand 3 phase motor/capacitor installation

[qaz]

Assuming the green wire was connected under the terminal cover how many more wires are in that cable.

yes it was. 3 more, red, blue , white.

will be back i bit later...its a sunny day here

 

[Pete999]

yes it was. 3 more, red, blue , white.

will be back i bit later...its a sunny day here

As it is in sunny N/ton

 

[westward10]

The problem is the whole set-up is somewhat dangerous and Heath Robinson. It is possible it has never functioned correctly or could be a duff/incorrect capacitor. Either way getting a three phase motor to run from single phase is never practical as the motor will never run efficiently.

 

[PEG]

Every time i have a potters wheel problem,a long haired ghost from the eighties,turns up,behind me....right weird...

 

[qaz]

The problem is the whole set-up is somewhat dangerous and Heath Robinson. It is possible it has never functioned correctly or could be a duff/incorrect capacitor. Either way getting a three phase motor to run from single phase is never practical as the motor will never run efficiently.

yes i accept that, thankyou . sorry to re post this question but is the following correct assumption on my part: its a 3 phase more running from a 1 phase supply, so, it must have been converted, hence the capacitor. is this pretty certain from what people here can see?
thanx

 

[westward10]

It is difficult to say without physically being there but the inclusion of a capacitor which is not required for a three phase squirrel cage induction motor suggests an attempt to run it from a single phase source.

 

[sinewove]

Are you sure it's a 3 phase motor, from your description it sound like a single phase job can't be sure though without a pic of the rating plate.

I'm a qualified mechanic but always tackled small electrical jobs without incident. wonder if i can get some advice re a 60's potters wheel.

it consists of :
-a 220-250 volt 3 phase, c/s 50, motor
-an largish oval capacitor [with a resistor between the 2 contacts] some distance away from motor. A 2 core cable runs from the switch box directly to the capacitor.
-a switch box on outside with 2 buttons, one for on and the other i assume is reset or off.

when switched on it runs extremely slowly for 10 seconds then stops, if you wait for a minute and press what i assume is the reset button, it will start again.

during the 10 seconds it runs you can stop it with one finger at which point it reverses direction.

any help in understanding this installation and why its not working would be much appreciated
m

According to my motor textbook,the capacitor for a 1 to 3 phase conversion on a 3/4 h motor is 30mfarad.It may be worth fitting a new capacitor if you feel confident.
Regards.S

 

[qaz]

According to my motor textbook,the capacitor for a 1 to 3 phase conversion on a 3/4 h motor is 30mfarad.It may be worth fitting a new capacitor if you feel confident.

thanks , i will make note of the suggested capacitor but agree it may be a botch, however it apparently ran well for many years on single phase . it was built in the 60's not 80's as Peg mentions in his joke, which i can't fathom

providing i can find a single phase motor that physically fits is the rest straight forward ? [assuming i know something about electrical systems] Regards.S

 

[Deleted member 26818]

In the photos showing the contactor connections are some data plates.
Can’t see them too clearly, but in one, you can clearly see 240V.

 

[qaz]

In the photos showing the contactor connections are some data plates.
Can’t see them too clearly, but in one, you can clearly see 240V.

is thaT GOOD?

 

[qaz]

i appreciate it may be a botch, however it apparently ran well for many years, so i may try to fix it , but im also very interested in fitting a single phase motor, is that straightforward?

 

[marconi]

See if you can trace the wiring to come up with a diagram which looks like the star one on the right (Steinmetz circuit):

 

[sinewove]

is thaT GOOD?

As others have said,the 3 phase motor must be connected in delta to work off 240v.The capacitor produces another phase.Live and neutral go to 2 motor terminals and the capacitor goes between live and the other motor terminal.Nowhere near as efficient as running on true 3 phase.
Regards,S

 

[westward10]

It doesn't produce another phase it induces a shift in phase to one of the windings effectively kick starting the motor.

 

[Deleted member 26818]

I think it would be an idea to have a look at the other data plates which are partly shown in the photos of the contactor terminations.

 

[qaz]

I think it would be an idea to have a look at the other data plates which are partly shown in the photos of the contactor terminations.

thats interesting, am starting to see the complexity of it. are the data plates the ones inside the plastic box, i couldn't see the mention of "240v"
am starting now to see where that "centrifugal switch" might come in

 

[Charlie_]

Does the motor spin freely, no bearing issues?
Do you know how to test a capacitor?

 

[qaz]

yes its free and bearing ok. i would luv to know how to test the capacitor.

i'm wondering if theres a clue in the fact [see first post] that the motor runs extremely slowly and for 10 seconds, at switch on [with no torque]

something I'm interested to know is why , in the first place would they use a 3 phase motor?. wheel probably built early 60's

 

[Charlie_]

Before my time but perhaps at that time most of the motors were manufactured the same but their individual control methods varied depending on application..or it could just be an hadoc build from a very resourceful electrician.

Few ways to test the capacitor;
Digital multi meter on the capacitor setting.. I don’t like this method

Do you have an analogue multi meter (not digital, type with a needle)

Set it to ohms and apply probes to corresponding terminals on capacitor, needle will move up high and then drop. If nothing happens then it’s not charging..

Other way is to get say a 9v battery, apply to the capacitor and charge it up.
Set meter to dc V and the reading should be about 9v and then it will discharge quickly through the multi meter

 

[PEG]

Has this machine got,or has it had,a speed control pedal?

I would be tempted to convert to single phase,as this is your supply,and add a pedal....

If i can remember correctly,from Mrs. Furness's pottery class...a speed control pedal,and a clay shaving tool,scraped on the side of the wheel...makes it sound like you are driving a formula one car...
Add a bit of exaggerated Murray Walker commentary...and voila! a trip to the headmaster's office...