Delay for 2 speed 2 winding single phase motor

[MAubrey]

Hello there …

I have been tasked with Coding certain portion of a program for control of what I think is a single phase 2speed 2winding motor. I am pulling from my experience with three phase motors but not sure if the same is transferable to single phase.

- there is only 2 contactors, labelled low and hi
- 120volt motor / 1.5hp / 60hz
- motor is driving a centrifugal water pump (all piping and connections are 2”)
- not sure of GPM of attached pump
- low speed, rpm —- high speed, rpm
- head pressure on entire system is only 3 feet
- motor has no issue starting from dead stop to low speed or from dead stop to high speed. Must be a shared centrifugal sw/starter coil?


Control scheme

from low to high, no delay required but standard interlocks where low speed controls/relays break before high speed controls/relays make.

From high to low, delay required where high speed control/relays break —- DELAY (250mS-1000mS??) —- low speed controls/relays make. what would be considered too short or too long of a delay is what I am struggling with?

Is it really that critical as in larger setups?

Thanks

 

[waross]

I would use enough delay that the motor is at or below the lower speed before it is energizes at the lower speed.
Energizing at speeds above the lower rated speed may lead to abrupt deceleration, which may cause loosening of the impeller in some pump designs.

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

 

[MAubrey]

@ waross … ok thanks. So we’ll have to get our mech eng in to get us some actual numbers on shaft hi and low speed and also deceleration times, then I can go from there… in the meantime ill just program an excessive delay where the motor’s speed will be at or darn close to stop before energizing low speed…

A Motor is a motor… don’t know why I expected a single phase motor timing to be non critical.

Thanks for confirming and clearing up …

 

[FacEngrPE]

If this is actually a two speed motor I would expect to find some indication of that on the label plate. A picture or typed copy would be illuminating.

It is possible that you have a shaded pole motor like this

https://www.grainger.com/product/CENTURY-Farm-Duty-Motor-2-60WD71

, 2 HP, which is about as large as this sort of motor gets now days.

 

[waross]

Despite the description that is not a shaded pole motor.
That is a capacitor-start/capacitor-run motor.
That is also a reversible motor.
Shaded pole motors are not easily reversible.
Shaded pole motors are reversed by removing the rotor and end bells, turning the stator and for end and re-installing the rotor and end bells.
1/4 HP is a large shaded pole motor.

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

 

[MAubrey]

Yeah, i have never seen shaded pole motors larger than fractional HP but then again, there is always more to learn and see.

This is definitely a standard single phase 2speed, 2 winding (i think internally its 2 windings????), motor. Low speed, 3.9amps/1725rpm and high speed, 12.2amps/3450rpm.

Its hard to get a good picture but ive attached what i could get. Its actually labelled a “spa motor” ??? LOL??

 

[che12345]

"... there is two a Lo and a Hi contactor...."
I take it from here, assuming the other parts (capacitor, centrifugal switch, if any) are in order, for your consideration:
1. From stop to:
a) Lo speed, immediate i.e. no time delay.
b) Hi speed, close Lo speed contactor. After some time delay*, open Lo contactor and close the Hi contaotor. Time delay* (transfer Lo to Hi speed) when reached full Lo speed.
2. From running Hi speed to run at Lo speed:
a) off Hi speed contactor, Time delay** (transfer from Hi to Lo) when speed dropped to about the Lo speed, close the Lo contactor.
3. Above proposals are intended to avoid big speed change from Lo-to-Hi or Hi-to-Lo, which are detrimental mechanically and electrically.
4. Note: Transfer time delay by speed needs a speed detector+monitoring relay, which are costly. Alternatively, using a time delay relay which need not be of very high precision, is simple and at very little cost.
Che Kuan Yau (Singapore)