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Connection of a 380V three-phase motor on 220v single-phase.

When there is a three-phase motor to connect to a single-phase sector, there are several solutions.
This is the capacitor assembly that will be discussed

Connecting a three-phase motor to mono with a capacitor drops its power output. We lose on average 30% of useful power and 50% at startup.

In cutlery this system will work well for machines that do not start under load, for example a drum or a polisher. Do not use this assembly for engines that start charging or high power as a back stand or pestle.
All systems with capacitors are still tacking, which can work well, but the result is never guaranteed, you must try and test.
A capacitor can be bought nine (pieces of appliances) but also recover on an old engine or a washing machine. Always make sure that it is a capacitor for 230V AC (thus non-polarized) and for continuous motor operation. Plastic-wrapped capacitors (called "self-healing") should be preferred to those packed in aluminum (old generation).
To reverse the direction of rotation of the motor, it is necessary to cross the 2 wires of the sector.

To connect our 380v tri motor in 220v mono (phase + neutral), we will use the triangle coupling.

We will connect for example: the phase in "u", the neutral in "v", and it will be necessary to add a capacitor between "v" and "w"

Very important !
The capacitor must have a voltage greater than 230V and must be AC ??~, NEVER use a polarized capacitor otherwise it will explode!
The usual value of the capacitor is expressed in micofarad "µf"

To find its value it is enough to multiply the power in CV by 50.

Example: a 250w motor (0.25kw)
 to begin, you have to convert Watts into horses. for this we divide the watts by 736 (1 CV = 736 W)

In our example 250/736 = 0.34 HP, our engine is 0.34 HP.

To find the value of the capacitor: 0.34 x 50 = 17, so to operate the motor of 0.25kw requires a capacitor of 17 μf.

If the value of the capacitor is less than 17 μf, the motor will work much worse, or not at all.
If the value is greater than 17 μf it is not annoying at all.


  C = 50 x P
C = value of the capacitor in micro farad "μf"
P = engine horsepower

*** Help: Conversion ***

To convert from kw to w:

w = kw x 1000 ------- example ------- 0.25 kw x 1000 = 250 w

To convert w (watts) to CV (horses):

CH = w / 736 ------- example ------- 250 w / 736 = 0.34 hp

*** Help: Capacitors ***
If you do not have a capacitor of the right value, you can associate several:


Connection of several capacitors
- On additionne leurs valeurs si il sont branché en parallèle.

ex: C1=10 µf et C2=15 µf => C total = 25 µf

- On additionne l' inverse des valeurs en série.

ex: C total= 1 / ( ( 1 / C1 ) + ( 1 / C2 ) )

( 1 / 10 ) = 0,1 ; ( 1 / 15 )=0,0666666

( 1 / 10 ) + ( 1 / 15 )=0,1666666

1 / ( ( 1 / 10 ) + ( 1 / 15 ) ) = 6

C1=10 µf et C2=15 µf => Ctotal = 6µf

*** Aide: le bornier du moteur***

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