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# Convert Three phase AC to Single Phase 24V DC

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#### hardik.patel

##### Member level 5
Hi friends,

Kindly Solve my below query,

I have very good idea about single phase to DC Conversion.
(single phse AC-->step down-->rectification-->filter-->Fixed Voltage IC(78XX) )

I need to convert Three phase AC to Single Phase 24V DC For my Low Voltage Circuits as a Power Supplies.

Kindly suggest me best idea which protect the followed circuits from voltage variation damages.
(i.e i need constant and smooth DC o/p from 3-phase AC)

- - - Updated - - -

1) one phase and neutral method
2) three phase to single phase transformer
3) SCR as rectifier

but not used any1 practically so confused to select which one for achieving above task.

Hi friends,

Kindly Solve my below query,

I have very good idea about single phase to DC Conversion.
(single phse AC-->step down-->rectification-->filter-->Fixed Voltage IC(78XX) )

I need to convert Three phase AC to Single Phase 24V DC For my Low Voltage Circuits as a Power Supplies.

Kindly suggest me best idea which protect the followed circuits from voltage variation damages.
(i.e i need constant and smooth DC o/p from 3-phase AC)

- - - Updated - - -

1) one phase and neutral method
2) three phase to single phase transformer
3) SCR as rectifier

but not used any1 practically so confused to select which one for achieving above task.

I think you make a mistake in "DC single phase" term first. No DC has any "phases".
If you need to use a 7800 line of voltage regulators, they can give you 1A max output at 24 V (7824). You will need a ONE phase transformer from 110 or 230 V (depends on where you live) to 25 V, then use a rectifier and a 1000 uF capacitor before connecting the 7824 regulator.
Be sure that your voltage to regulator will not exceed 35 V, otherwise you will kill the regulator. Use a small lamp as a dropping resistor, and add a 32 V Zener to prevent any spikes.

Any 24 V, 1A power supply only needs one phase AC primary source. Only very high load currents like more than 10 A may need a three phase transformer to distribute the load.

hardik.patel

### hardik.patel

Points: 2
An additional comment about three-phase to DC conversion. Mentioning 78XX suggests that you are talkig about low power DC.

So the only reason to connect to more than one phase of the three phase supply could be that you are missing a neutral line. In this case, you can use a single phase transformer with 400 respectively 200 VAC primary voltage and connect the input phase-to-phase. It's often done in industrial automation. Maybe that's what you meaned with a "three phase to single phase transformer".

"SCR as rectifier" isn't but a bad idea for low power DC supply. Also conflicting with most power quality regulations.

hardik.patel

### hardik.patel

Points: 2
Dear jiripolivka & FvM,

Altimately you are saying that i need to take 1 phase (among 3 phase) and Neutral..then connect these 2 terminals to the Primary winding of transformer??...am i right?

Or please paste if any link of that circuit is available...so that i can understood clearly.

Provide the term "rectifier" in wikipedia. You will get the brief idea about the process involved.

Dear jiripolivka & FvM,

Altimately you are saying that i need to take 1 phase (among 3 phase) and Neutral..then connect these 2 terminals to the Primary winding of transformer??...am i right?

Or please paste if any link of that circuit is available...so that i can understood clearly.

The problem is not in what AC terminals to use, but your situation.
In an ordinary home you have a wall AC socket to connect your AC-DC power supply.
Usually it is 110 V in USA and Japan, 230 V AC elsewhere. Those voltages may be taken from one phase like "phase" and "neutral".
Where you have a 3-phase connection, like in the industry, you can take the same as above, or "phase 1 to phase2" which is a higher AC voltage, like 220 or 380 V.
Whatever above you choose is correct. You only must buy an AC transformer designed to one of the above voltages for primary, and secondary as I suggested, 25...28 V to which you connect a rectifier and 7824 voltage regulator. Make sure the transformer is well made and well isolated for your safety. Good transformers are tested by 3 kV for isolation.
When you order the transformer, you must know the power rating. For 7824 regulator, the maximum DC current it can deliver is one Amp. Therefore the transformer must be rated for 28 V x 1A= 28 Watts or more. Lower power rating would limit the load current before the DC regulator.

hardik.patel

Points: 2