How to Wire a Motor, 3 HP 3450 RPM

[kk027]

Ok, I have a motor which I think as per my inspection had bad contact plate and the owner was throwing it away. has no smell so I am trying to fix it up He had pulled start capacitor and run capacitor out and lost them. So I brought new contact plate, capacitor and need help wiring.
1. Two wires (120V each) are going to two different winding on left side.
2. On right side two wires from one winding and two from another is coming. It seems one from each was going to run and other to start capacitor. I could be wrong does not want to wire incorrect.
3. So based off these four wires I want to connect run capacitor and start capacitor. I have good electrical background, but this I have not done this before.
4. I need help determining start winding, run winding. Once I know these I can attach centrifugal switch and contact plate. Start capacitor will start the motor using start winding and as it speeds centrifugal switch will break that contact and make contact with run capacitor and run winding, that I know.
Thank you for help, let me know what I need to do.

 

[zsolt1]

hi,
make some measurements , measure resistence of coils to to see is they are similar . Go to an online calculator to get capacitor values for the 2kw motor

 

[kk027]

S CAPACITOR 600M 125V 1-7/8 X 3-3/8 and Run CAPACITOR 30M 250V 1-1/2 X 2-3/8 which are manufacture's specification, I have them already.
Now I forgot to add voltage like zsolt1 said. I checked the contact plate, the contact was bad so it would not start the start capacitor. However the contact that centrifugal switch would make for run capacitor was fine. Poor guy had taken to machine shop and I am sure they tear it down and never bother with contact plate. I would have purchase new motor, but this motor has weird plate to mount to motor.

Two power line 120 V( going into motor, say 1 & 2) each show continuity with each other. Both Line 1 and 2 shows continuity with wire 3 & 4, (3&4 to each other), but not to 5&6. 5&6 shows continuity to each other.
Thanks.

 

[zsolt1]

how many pairs do you have ? 1-2 ; 5-6 ; Two coils ? do they have same resistence (in ohms) ? if so 1-2 sould be supplied directly and 5-6 would be quadrature coil, supplied in series with capacitors (from same 1-2 points)

 

[kk027]

Hi zsolt1,
https://www.simplecircuitdiagram.com/2010/11/18/capacitor-startcapacitor-run-induction-motor/

Take a look at this. It might be what I am calling 3 & 4 is the two opposite wires from main winding and 5 & 6 the wires from start winding. It makes sense that line 1 and 2 would both show continuity with main winding. Is this my wiring diagram?
Thanks

 

[zsolt1]

hi,
that is your wiring diagram

 

[kk027]

hi,
that is your wiring diagram

Hi zsolt1,
Thanks. As it seems from diagram, the run capacitor is always on, only start capacitor gets disconnected by centrifugal switch. Is it true?
I say that because centrifugal switch has only two connections. If i am wrong, let me know.
Thanks

 

[FvM]

As it seems from diagram, the run capacitor is always on

That's why people call it run capacitor. Your considerations are correct.

 

[kk027]

That's why people call it run capacitor. Your considerations are correct.

True,
Seems I need centrifugal switch in hand to make decision. I looked a grizzly video which showed centrifugal switch was always on at beginning but then disconnects once 3/4 of speed specified is gained and then disconnect start capacitor. If my motor did not run at all,(as the guy i got it from said), start capacitor should have still started and stopped when speed cam up. But because Run capacitor would not make contact, it would then slow down until start capacitor pick up. The cycle would go on and on. Unless the contact was reversed.
I will update once so.
Thanks

 

[zsolt1]

hi ,
as you can see in the drawing you find , you have 1 coil of motor supplied directly . The other coil is supplied in series with capacitor . The capacitor has greater value at start (2 in paralel ) and lower value after startup.
Why?
The first coil is for supplying ac current in the rotor by induction . Like in a transformer just that the primary is the coil from stator and the secondary is the rotating coil in rotor. The rotor coil is short circuited so it passes current thru it and thereby it has own magnetic field, same phase as the one who created it. In order to rotate this structure a second magnetic field is required so that the interaction between them can produce torque (remember when playing with magnets ?). This is second magnetic field is created by the other stator winding in series with the capacitor.
Why is this second coil supplied through capacitor and not directly like first coil ?
Because without phase shift the magnetic fields of both coils (actually 3 coils) would be same and no torque would be produced. The capacitor creates phase shift of current in the second coil so it's magnetic field is not the same. At startup bigger phase shift is required since the rotor is at standstill .Actually interaction between fields is maximum at 90 degree . (quadrature)
When only running capacitor is available , and when mechanically possible , the startup can be made by hand with a rope. First a rope, previousely rounded on the rotor is pulled so it starts rotating , than the power supply is applied while the motor is in rotation , than the mechanical load is coupled . Actually this simple startup was used to avoid startup current when no startup circuit was available . At smaller motors was enough to hit the pulley in a direction , after the motor accelerated , the load could be coupled.
Ps: if no centrifugal switch available , you can use a manual switch to start up the motor . Just don't forget to decouple the switch . If the startup capcitor remains on, the motor will overheat because of no slipping between fields , the second stronger field (the one which creates quadrature) will slow down rotor

 

[kk027]

Zsolt1 thanks,
So it's fine if run capacitor is always on, just the start capacitor has to be disconnected after start speed has reached?
I just want to make sure everything is fine before I hit it, like I said the motor mount to my table saw is weird, and this has exact what I want.

 

[zsolt1]

yep , run cap always on

 

[kk027]

yep , run cap always on

Hi All,
I wired just as I thought, but now the rotation direction does not always seems to be the same each time I restart. Also it kind of not start instantly and few times tripped 15A 220V( 3HP is rated at 13A,220v) Feels like I am not doing something right. Or start capacitor is not giving the jolt.

Few things I did.
1. My earlier post, L1 & L2 are power in from right side. Left side had 3&4 and 5&6 in pairs. 3&4 showed continuity with L1 and L2(and between), but 5&6 did not( Between them yes).

I took stator out and powered only one L1 and the potential at 3&4 were close to 0. Between 5&6 and neutral was 34.5V. Same when i Powered L2 only. When both were powered together it tripped without any wire touching.


I looked few literature and saw 120V going to 600uF 125V (starter- centrigugal switch ) and run cap(250V 30uF in phase with it). Run cap had other 120V from other side. That's what I was trying to do in vain. All I wanted to see was two 120V between 3&4 and 5&6 or something. Any suggestion?
Like I said I have only 4 wires to work with.
Let me know what measurement I need to do or there is something wrong with motor.

 

[zsolt1]

hi,
if you wired up the circuit like schematic , and every component does it's job , the motor is faulty .

 

[kk027]

hi,
if you wired up the circuit like schematic , and every component does it's job , the motor is faulty .

Can we say that yet ? If motor is faulty, why does it turn full speed ? The fact that the direction is not same and kinds hesitate at the beginning makes me think a start cap is not pushing rotor in right direction. The run cap as its rotating the coil will follow the initial inertia which is random. I mean may be it is faulty, but I just wanted to try to locate where the fault is then?

 

[zsolt1]

measure capacitors , are they ok ? older caps dry out

 

[kk027]

They are brand new capacitors, I don't have capacitance measurement on my meter, but i will go get one now and check as well.

 

[zsolt1]

hmmmm.. new caps ... must be ok .Forget the caps. Do you see the the motors name plate ? Do you have an ohm meter ? Can you measure resistence ? You have 2 coils. What is their resistence ? It's important to know if they are identical . Some coils at some motors can have taps .You said that there are only 4 wires so this is not your case (4 wires>2 coils)

 

[kk027]

Well like I said L1 and L2 which are power in show continuity with 3&4 and 3&4 with themselves and resistance between these four lines is close to zero no matter which wires I inter connect.
5&6 show continuity with each other and zero resistance that's all, and with no other.
Caps are good, I measured their capacitance.

 

[zsolt1]

Close to zero ... probably ok . I had 0.75 kW motor , when ok it had 1.5 ohm at 20 'C room temperature, When faulty it had 0.47 ohm at room temperature (it cooled down until we unmounted ). Take care at details and precision , usually this makes difference .
if 34 shows 0.xxx and 56 sows 0.000 ohm that's not ok .
I have no experience with your motor so i can't tell what value you should have . An other motor i dialed with was a 12kW dc motor , the stator had 160 ohm and rotor phases had 1.5 ohm .
Did you try 56 powered continuously and 34 through capacitor ? if not try just to see how it behaves .
Don't worry fuses keep you safe :-D