Single / three phase motor

[Speedy Builder5Participant @speedybuilder5]

I dread even asking this question (Its been asked so many times), but I can't find the answer here or on the WEB. I have got a LEROY-SOMER-S fractional electric motor. It is labeled for both 3 and single phase. It has 6 wires coming from the field windings, no centrifugal start switch etc.
The coil pairs are:-
Red/Blue 110 ohms
Green/White 109 ohms
Yellow/Black 110 ohms

Red/Green/Yellow are currently commoned together.
The motor label says use a 5uf cap for single phase.
Any ideas as to how the cap and Blue/White/Black wires should be connected.
BobH

[Speedy Builder5Participant @speedybuilder5]

Wiring single phase

[Ian ParkinParticipant @ianparkin39383]

It's almost certainly a 3 phase only motor

You can wire it for 415v or 240v working

It's wired at the mo for 415 working (star)

Can you post a picture of the plate and is there wiring diagrams in the connection box /lid the cap may be to generated a phantom phase with a 5uf cap

You need to wire it as delta connection first then live to one corner neutral to another the cap to the last corner and the other side of the cap to live

Edited By Ian Parkin on 24/04/2016 19:34:28

[Ian ParkinParticipant @ianparkin39383]

So connect blue and green , white and yellow, black and red together…then live to black red neutral to blue green cap to white yellow then other side of cap to live

[Speedy Builder5Participant @speedybuilder5]

Label says 3 or 1 phase. See attached – photo ; not so good, but one label for 3 Ph and one for 1 Ph. I am interested in the 1 Ph. You can just read Capa 5uf (Bottom right of label).

[John Stevenson 1Participant @johnstevenson1]

Nowhere does it say single phase.

It says 220v and 380v volts NOT single pahse.

You can and do have 220v three phase

[EmgeeParticipant @emgee]

John

Says Ph 1 on the 2nd line from right on the right label. Ph 3 on the left hand label so believe it can be used single or 3 phase. The kW output stated seems to confirm this also.

Emgee

[Michael BriggsParticipant @michaelbriggs82422]

A bit odd that the labels state different type numbers, I would not expect a motor type number to change depending on how it is wired. Michael

[Clive FosterParticipant @clivefoster55965]

Posted by Speedy Builder5 on 24/04/2016 19:22:04:

I dread even asking this question (Its been asked so many times), but I can't find the answer here or on the WEB. I have got a LEROY-SOMER-S fractional electric motor. It is labeled for both 3 and single phase. It has 6 wires coming from the field windings, no centrifugal start switch etc.
The coil pairs are:-
Red/Blue 110 ohms
Green/White 109 ohms
Yellow/Black 110 ohms

Red/Green/Yellow are currently commoned together.
The motor label says use a 5uf cap for single phase.
Any ideas as to how the cap and Blue/White/Black wires should be connected.
BobH.

Its a reasonably modern motor so as the lable says "use 5µF cap for single phase" i imagine this quote from page 228 of the the first edition of the Electric Motor Handbook edited by E.H.Werninck and published by McGraw-Hill in 1978 applies :-

"In fan applications requiring only 0.25 to 0.4 p.u. starting torque the three-phase winding is also used for single phase supplies by employing a single start and run capacitor in what is sometimes known as Steinmetz connection. A 415 volt star connected three phase motor, when reconnected in delta to a single-phase 240 volt supply of the same frequency, with a capacitor across one of the other phases, may be expected to have an output rating of 70 to 80 percent of its three-phase value. The exact value of the capacitor will depend on the size of the motor and its electrical design, but for 240 volt motors with three-phase ratings of 180 to 750 W will be of the order of 10 to 60 µF. The single phase starting torque may however be as low as 10 percent and the pull out torque down to 60 percent of their three-phase values."

Certainly a legitimate rating and technique but such motors tend to be optimised for fan applications and are not terribly useful general purpose devices. Fans have a very predictable load, need little starting torque and generally are expected to run at constant speed. Optimising the motor for this work lets you squeeze out a few percentage points of efficiency at the cost of inherently low starting torque and relatively small speed range from nominal before pull out torque drops sharply. Lower starting torque comes with lower start surge current which is handy should you have a number of fans switching on at the same time. They tend to run hot outside their operating range. Doesn't help that many types use simple, finless, cases and rely on fan air to help cool them. Not quite in the same self-destruct league as the highly efficient pseudo two-phase single-phase motors also used on fans which are well known to self immolate if left running unloaded for more than afew minutes and will stall if you look at them harshly.

For single phase use simply connect the three coils in a series ring (delta). Put power across one winding and hook the capacitor, which must be a motor run type, between the live and the floating terminal where the other two windings join. Reverse one set of connections to reverse the direction of rotation.

Clive.

Edited By Clive Foster on 24/04/2016 21:25:11

[John Stevenson 1Participant @johnstevenson1]

Sorry, brain fart

[Speedy Builder5Participant @speedybuilder5]

Thanks for all your ideas. Although there are 3 wires commoned together (Red/Green/Yellow), apart from taking it apart, is there a way of telling that these are commend correctly and that one coil is not "fighting" the other two?
Bob

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