# Can I give a two-phase input to a single phase input of the SMPS?

Thread Starter

#### shetsachin

Joined Jul 5, 2017
23
I have a XLG mean well SMPS that has a input range between 100VAC to 305VAC, but in this SMPS two phase input has been given. i.e phase to phase voltage is 230V, phase to earth is voltage is 115VAC. This SMPS failing frequently within a month of operation. my doubt is it a problem to give two phase input to single phase input of a SMPS?

#### Sensacell

Joined Jun 19, 2012
3,331
How do you connect this? please provide a diagram.

Why connect it with 2 phases?

Thread Starter

#### shetsachin

Joined Jul 5, 2017
23
How do you connect this? please provide a diagram.
ans:
Attached.

Why connect it with 2 phases?
ans:
because need 230V for the SMPS. but the line voltage is max 115V only. so taken two phase from the supply and given to input of the SMPS.

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#### Ian0

Joined Aug 7, 2020
8,978
If phase-to-earth voltage is 115V, then phase-to-phase voltage is 200V, not 230V, because phase-to-phase voltage is √3 x phase-to-neutral voltage, because the phase voltages are 120° apart, not 180°.
Having said that, there is no good reason why the power supply will be less reliable on 200V than it would at 115V. In fact, it will generally run slightly more efficiently from a higher supply voltage.
Does it have enough cooling?

#### Ramussons

Joined May 3, 2013
1,374
How do you connect this? please provide a diagram.
ans:
Attached.

Why connect it with 2 phases?
ans:
because need 230V for the SMPS. but the line voltage is max 115V only. so taken two phase from the supply and given to input of the SMPS.
The way 2 phases of a 3 Phase system is connected, you will still get only 110 volts across L-N, the input. Earth cannot be used as a reference point for the input.
The 2 Phase lines are not 180 degrees apart for an addition, they are 120 degrees apart, and the addition is still the same.

#### crutschow

Joined Mar 14, 2008
33,370
What you have is not 2-phase (two voltages out-of-phase by 90°), it is 3-wire "split-phase" with the two hot wires 180° out-of-phase to neutral.

#### Ramussons

Joined May 3, 2013
1,374
What you have is not 2-phase (two voltages out-of-phase by 90°), it is 3-wire "split-phase" with the two hot wires 180° out-of-phase to neutral.
No, its not a "split phase". The Primary of the transformer is a Delta, which means that it is a Real 3 Phase 120 degrees apart. The secondary follows the primary, except it is a Y formation.

Thread Starter

#### shetsachin

Joined Jul 5, 2017
23
The way 2 phases of a 3 Phase system is connected, you will still get only 110 volts across L-N, the input. Earth cannot be used as a reference point for the input.
The 2 Phase lines are not 180 degrees apart for an addition, they are 120 degrees apart, and the addition is still the same.

yes, What you have said is correct. both two phase addition makes ≈230V AC.
The thing is I want to know whether two phase ≈230VAC (Phase1 and Phase2, 120 deg phase shift) can be connected to single phase ≈230VAC device (Line and Neutral)?

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#### MaxHeadRoom

Joined Jul 18, 2013
28,069
yes, What you have said is correct. both two phase addition makes ≈230V AC.
The thing is I want to know whether two phase ≈230VAC (Phase1 and Phase2, 120 deg phase shift) can be connected to single phase ≈230VAC device (Line and Neutral)?
There is no difference in the end result between a N.A. style 1ph C.T. transformer secondary and the 1phase source derived from the two phases of the 3ph transformer.
Any device connected to either cannot tell the difference.
BTW, one only becomes a neutral in this case is if you earth ground it
The exception is the star point of a 3ph transformer which is always the neutral.

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Thread Starter

#### shetsachin

Joined Jul 5, 2017
23
There is no difference in the end result between a N.A. style 1ph C.T. transformer secondary and the 1phase source derived from the two phases of the 3ph transformer.
Any device connected to either cannot tell the difference.
BTW, one only becomes a neutral in this case is if you earth ground it
The exception is the star point of a 3ph transformer which is always the neutral.
Thanks for the information. @MaxHeadRoom.

#### Ian0

Joined Aug 7, 2020
8,978
It's a moot point, but it will be 200V not 230V as the phases are 120° apart not 180°, but it is still within the acceptable range for the power supply.

#### Ramussons

Joined May 3, 2013
1,374
It's a moot point, but it will be 200V not 230V as the phases are 120° apart not 180°, but it is still within the acceptable range for the power supply.
It will be 230 Volts.

#### Ian0

Joined Aug 7, 2020
8,978
It will be 230 Volts.
Not wired across two phases on three-phase 115V phase-to-neutral , it won't. Show me your vector addition!

#### BobTPH

Joined Jun 5, 2013
8,156
but it is still within the acceptable range for the power supply.
But then, so is the 115V to neutral.

Bob

#### Ian0

Joined Aug 7, 2020
8,978
But then, so is the 115V to neutral.

Bob
Exactly - if it's unreliable on 115V, then I'll bet it will be just as unreliable on 200V.