# 480V 3-Phase AC to DC 12V

I am trying to figure out the best approach to convert a 480V 3-phase AC to a 12V DC. I am thinking of first converting the 3 phase to a single phase AC then using a transformer and rectifier shown in this link Transformer and rectifier to get 12V DC.

1. Is this the right approach or can anyone suggest better approach?

2. To Convert a 3 phase to single phase can we use one of the phases and a neutral wire in a 3-phase 4-wire system and give it as an input to the above transformer and rectifier or is this a bad idea?

Thanks

• Well, it only goes up to 265V. I'm assuming 480V is line. – StainlessSteelRat Apr 11 '17 at 19:54
• You don't say how much power you need but a phase to phase 480 Vac to 12 Vac is always possible to wind/order and rectify it from there. – winny Apr 11 '17 at 20:48
• You can use one phase as power SMPS which link you gave is not very big. To reduce voltage before the SMPS you can use a half-wave rectifier with protecting. Or change the hot part of the SMPS. – AltAir Apr 11 '17 at 21:18
• The socket, plug, and suitable (safe) cable for 480V 3phase is very bulky and expensive. If you need some 12V power, find (or get an electrician to install) a lower voltage power tap. – Whit3rd Apr 12 '17 at 11:31

Phase to neutral for 480 V 4-wire is 277 V. That is outside the 85-265 V range specified for the linked power supply. You need a power supply with an upper voltage limit of at least 305 V to allow for 10% over-voltage. A 15% margin or more would be preferable. I would get a 480:120 transformer to use with a purchased power supply.

I am trying to figure out the best approach to convert a 480V 3-phase AC to a 12V DC. I am thinking of first converting the 3 phase to a single phase AC ...

You cannot convert three-phase to single phase using transformers other than by dropping two of the phases as you suggest in your last paragraph.

To Convert a 3 phase to single phase can we use one of the phases and a neutral wire in a 3-phase 4-wire system and give it as an input to the above transformer and rectifier or is this a bad idea?

Yes, it's a bad idea. It puts all the load on one phase when you could have a three-phase balanced load.

Is this the right approach or can anyone suggest better approach?

A very simple and economical approach is to step the voltage down with a 3-phase transformer and rectify it.

Figure 1. 3-phase rectifier. Source: if a standard three-phase 400V AC connection is rectified what DC voltage comes out of it?.

The DC voltage obtained will be very close (about 95%) to the transformer peak output voltage less the diode voltage drops. Therefore to get 12 V out the transformer secondary voltage should be: $$V_{IN} = \frac {1}{\sqrt 2} (12 + 2 \times 0.7) = 9.5\ \mathrm V$$

Figure 2. 3-phase transformers are available in sizes from 100 VA or so up to magawatts.

DC power supplies are available similar to that of Figure 2 complete with built-in rectifiers.

I have the same setup due to crypto mining.

solution 1 a) use a 480vac 3phase to 208 3phase PDU such as Liebert PDUs (ie 225kva Liebert) b) connect 208vac 3phase breakers to power strip 3phase PDU (ie 60amps HP/Dell PDU which gives you like 6 sockets in C19 socket) c) connect the PDU sockets to a PSU such as the 2880w IBM PSU which gives you a bunch of 12V PCIE cables for the miners or whatever you're doing with the 12VDC

solution 2 which requires no step down transformer/PDU

a) wire up a bunch of 277v breakers in your 480 3phase panel and connect them to a single phase PDUs with like 6 sockets, wire each socket to a 1400watts 277v PSU such as the AMP1400Y1 / Z1 PSU which will gives you a bunch of 12V PCIE cables for the miners or whatever you're doing with the 12VDC.

• This is like a 'me too' type of answer. Make it seem like your own creation or 'worked with' semantics, and you will get more up votes. Also fix up your grammar, and be consistent with paragraph titles; Solution1), Solution2), etc. – Sparky256 Mar 19 '18 at 21:56

I would suggest to rectify all three phases, then use a flyback DC/DC. There are plenty of them, i personally like ST viper.

To answer the second part, if you have a 4 wire 3 phase system your rated voltage is 277v between one leg and the neutral therefore the transformer in the link will not work

Or... just go buy a 480-24VDC power supply. Lots of people make them. Line side will be single phase 480V line to line, load side is 24VDC. Why make this more complicated than it needs to be?

• OP wanted a 12 V PSU not 24 V. – Transistor Jul 31 '18 at 19:08