Single Phase Deep Borewell Pump with 3 Capacitors or Single Capacitor

I am not an electrical engineer, but I assume that three capacitors are used to emulate a 3 phase starting system, as there is not the room or the right conditions deep down on a borehole pump to use a single capacitor starting system. If this is correct then there would be nothing to gain from using a single capacitor starter, regardless of how cheap it is.

I read you asked for an expert, which i'm not, however are you absolutely sure that the third unit you saw was in fact a cap?. Typical borehole control boxes for single phase have a start and run cap and an overload protector. This o/l protector LOOKS like a cap if you look at it from above, or direct on. The caps and o/l all sit on end and their wiring points are on the same plane (their terminals face the viewer, side by side) I see no need to "emulate" 3 phase as there is nothing to gain. You can manipulate a single phase to be 3 phase, but your losses and usable power make it a costly venture.

The three capacitor varieties are used for, converting single phase to 3 phase motor operation. In comming 2 wire will be converted to 3 wire out put for the motor as R,Y,B.

The single capacitor unit is the one, used as motor start capacitor for single phase motors. In this case also three wires will be supplying power to motor, Phase, neutral and speed switch (centrifugal switch to cut off the capacitor once the designed speed is reached). This is the one you have to buy.

the capacitor with the biggest value is mostly the start capacitor

the capacitor with the medium value is mostly the run capacitor

the capacitor with the smallest value is to improve the power factor of the motor

Single phase pump motors and three phase motor have common starter kit box. So they have marking for three phase connection, R Y B. Same box is used for single phase motor as well.

Single phase motor can be of Capacitor start only (with one capacitor only and is cheaper, but the power factor of this type of motors is low and have poor efficiency). Other type is capacitor start capacitor run. This type motor has two sets of capacitors. One for starting purpose which is taken out of circuit after motor attains a pre-determined speed at which a centrifugal switch operates and takes out this capacitor. Other capacitor is the one which remains in running winding of the motor and keeps operating power factor at desired value.

Single phase supply can only be converted to two phase supply by introducing a capacitor in one of the windings but no to 3 phase balanced supply.

Dear sir,

Any single phase motor will have two seperate windings.In motors that are

fixed on ground we can have the starting capacitor & the centrifugal switch in the

motor itself. This not possible to fix it in the submersible pump as this will pose

repair and maintenance problems. The three wires are to connect the capacitors

and not to be confused with Three phase -RYB. So you find the three capacitors

one for starting , one for running connected through a timer -( instead of a

centrifugal clutch) & one for possibly for power factor improvement (This is seen

very rarely in practice). I am not an expert on pumps but an electrical engr.

Hope my answer clears your doubts.

Manroop.Chennai.

Take a look here. Enclosures Standard boxes

http://submersibleborepumps.com.au/control_boxes_single_phase.html

Contact the pump manufacturer for advice, definitely before the connections are made and the pump is lowered down the well!