Motor Wiring diagram confustion - P1/P2 ?? 1

[PaulKraemer]

Hi,

I am trying to troubleshoot a machine that has a blower with a single phase motor. The manufacturer of this machine sent us this blower as a replacement for a different one that had worked fine for quite some time, but then failed. The nameplate and wiring diagram for the new blower are shown below ...

... The wiring for this new blower/motor is different than that for the one we are trying to replace. I know that the old blower worked when we applied 205 VAC across two of the motor terminals, without requiring us to do anything else. The manufacturer told us that this new blower should work if we follow the "High" diagram on the wiring diagram and apply 205 VAC across terminals U1 and W1. There are actually two "High" diagrams. The one on the left shows a jumper between terminals W1 and V2. The one on the right shows wires labeled "P1" and "P2" connected to W1 and V2. At the end of P2, there is a triangle that appears to be making contact with a line at the end of P1.

Currently, I have no documentation on this blower other than what I have shown above. I have requested information from the blower manufacturer, but I was wondering if anyone here might be able to tell me what this P1/P2 connection might be?

Any suggestions will be greatly appreciated.

Thanks in advance,
Paul

 

[waross]

P is protection. This is an internal thermal trip, wired in series with the motor.
It appears that not all similar motors incorporate this feature.
If there are P1 and P2 leads, than connect them as shown.
If there are no leads marked P1 and P2, use the other diagram.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[PaulKraemer]

Thank you Waross - that is a big help!!

Just for my own knowledge, would you say the wiring diagrams I showed previously indicate that this is a capacitor-start type motor, a capacitor-run type motor, a combination of the two, or that the diagram does not show enough information to make this determination?

I don't have much experience with motors that have capacitors, so I figured I'd do some reading up on them. 15 minutes of googling reminded me that some motors make use of a capacitor during startup and then take it out of the circuit once the motor is running, others keep the capacitor in the circuit the entire time while running, and others include both a startup capacitor and a "run" capacitor.

If you can help me determine which type of motor I have, it will help me focus my reading.

I appreciate your help.

Best regards,
Paul

 

[waross]

Capacitor start motors are very common. They may be identified by the click as they accelerate and a click followed by a slight dragging noise as they coast to a stop. You may be able to see the centrifugal switch through the ventilation holes on the back of the motor.
PSCs or Permanent Split Capacitor motors are generally used in smaller sized motors.
One variation is a small motor with two identical windings. L2 goes to a common connection and L1 goes to a double throw switch with off position, or a similar relay.
Whichever winding is fed directly, becomes the run winding and the other winding, fed through the capacitor becomes the start winding.
This makes a very simple circuit with only three wires coming back from the motor and the simplest reversing circuit.
This is often found in small positioning motors in applications such as air handling dampers, or motor operated valves. There may be end of travel limit switches on the dampers or valves so that the motor circuit may be left energized in either direction.
That is, put the switch in the open position and the motor will run until the open limit switch is reached, put the control switch in the close position and the motor will run until the close limit switch is reached.
When end of travel limit switches are used, the control switch or relay need not have an off position.
This makes for a very simple reversing control circuit.
A capacitor start, capacitor run motor may use one value of capacitor for starting and another value, optimized for running conditions and current to get extra torque out of the start winding instead of letting it sit idle when the motor is running.
And some capacitor start motors may have across the line capacitors added to improve the power factor.

Looking back at your motor, this is a typical, dual voltage single phase motor.
The motor has two 115 Volt run windings and one 115 Volt start winding.
For low voltage operation, all three windings are connected in parallel.
For high voltage operation, the run windings are connected in series, and the start winding is connected from one line to the series jumper between the two run windings.
Look for the run windings between U1 and U2 and between V1 and V2.
The start winding is between W2 and U2.
There is no internal connection between U1 and W2, only the external connection of the capacitor.
Likewise, there is no internal connection between W1and V2. The connection is made either by the protection device or by the jumper link.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Some small single phase motors use a high resistance start winding to develop the phase shift needed to develop the starting torque.
Starting torque is poor, These are often found driving fans. 1/4 HP would be a representative size of this type of motor.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Your motor is probably a capacitor start motor. Listen for the click and drag of the centrifugal switch. Failing that look in the vent holes or carefully pull the end bell off and look. The switch will be on the non-drive end.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!