trying to understand 3 phase motor/capacitor installation

[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...

 

[marconi]

Re qaz #38: 'why would they use a three phase induction motor in the first place?'

I think a possible reason might be found in the torque-speed plot below, but first study the plot for the three phase motor supplied by a Steinmetz circuit at my #32 - as the rotational speed reduces so does the torque.

For a single phase induction motor, as the speed reduces from normal running speed the torque reduces until the centrifugal switch closes whereupon the torque jumps up because it is boosted by the auxiliary winding. I am not a potter but I suppose this is undesirable - the potter would prefer to control the speed with the torque he applies with his hands and without the jump up in torque ever happening.

 

[qaz]

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

right, i'll test with an analogue meter today and post results. to answer another question the speed control is via a rotating cone , so no pedal

 

[qaz]

[ I am not a potter but I suppose this is undesirable - the potter would prefer to control the speed with the torque he applies with his hands and without the jump up in torque ever happening.

not quite like that, unless i'm mis reading you. the potter needs continuous, smooth torque , but yes, certainly a jump in torque would not be good[/QUOTE]

 

[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.

i cant find that photo, which is it pls

 

[qaz]

update: i foolishly tested the capacitor with motor off but still plugged in, i got a flash at the probes

the capacitor tested ok with analogize meter

for a couple of attempts the motor behaved as before i.e. running for 10 secs then off. then to my surprise it ran continuously but still at the extremely slow speed exactly like before. it also smokes quite nicely as it runs [it may have smoked before but not for long enough the notice]
thanks in advance for any more input