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    3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering application

    I am currently working on a 3 phase energy meter project. I don't have a lot of experience in designing power supply circuits (AC/DC) let alone a 3 phase 4 wire one (L1,L2,L3 and N) with a transformer to be galvanically isolated. Since energy measurement is being done for all three phases, the metrology (Microcontroller + metering IC) part must be able to measure energy even if two phases go out, so AC supply must come from all three phases. I've scoured the internet and found a few approaches, some used a transformer, some didn't.

    1. My findings


    TI and AD have a few application notes for whole energy meters but their power supplies are transformer-less (bummer).

    ST has a lineup called VIPER (rectification then flyback DC/DC) which has a transformer based schematic but for prototyping i think the design will take some time to perfect and i'm looking for a faster temporary solution to focus on the computing part of the system for now.
    2. My questions

    Can i use something like this ( IRM-20-12 ) for the time being or if there is a better model please let me know. If the answer is yes then i think the next question is how do i connect it to all 3 phases since the power module only take Line and Neutral ?
    Click image for larger version. 

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    If the answer for the previous question is no, what would be my options for a prototyping stage and another for a cost efficient and not so brutal to design ?

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    Re: 3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applica

    Is your meter portable? Can it run on a 9V battery? Or several rechargeables?

    Is your meter installed permanently? Can you power it from a wall receptacle?

    It sounds like unnecessary trouble to make a 12V 1W supply that draws from 3 sources, and needs 3 transformers. Your 12V does not need to be referenced to 3-phase ground nor high voltage, because looking at your diagram, it implies optocouplers measure your high voltages.



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    Re: 3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applica

    Hi,

    I also see no need for a 3 phase power supply.
    It seems that "3 phase" is important for you .... but your sketch does not show it.

    Please show a sketch that explains your concerns.

    12V, 100mA gives 1.2W... why do you need that much power for an energy meter?

    Klaus
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    Re: 3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applica

    Quote Originally Posted by BradtheRad View Post
    Is your meter portable? Can it run on a 9V battery? Or several rechargeables?

    Is your meter installed permanently? Can you power it from a wall receptacle?

    It sounds like unnecessary trouble to make a 12V 1W supply that draws from 3 sources, and needs 3 transformers. Your 12V does not need to be referenced to 3-phase ground nor high voltage, because looking at your diagram, it implies optocouplers measure your high voltages.
    First of all my apologies for not making the post clearer, the picture above is the block diagram of the suggested IRM-20-12 module ( it's all in there ).

    Meter will not be portable. The meter will run on a backup battery 1/2AA +1F super capactior ( in backup mode).

    Meter will be installed permanently. The evaluation board of the metering IC is running from a wall receptacle, but for a real world application i need it work on all 3 phases.

    I'll admit i'm aiming too high as in terms of power budget. My aim was to maybe have a wide supply for the first prototype and then surely the supply will go down since i dont really have the power budget pinned down.

    - - - Updated - - -

    Quote Originally Posted by KlausST View Post
    Hi,

    I also see no need for a 3 phase power supply.
    It seems that "3 phase" is important for you .... but your sketch does not show it.

    Please show a sketch that explains your concerns.

    12V, 100mA gives 1.2W... why do you need that much power for an energy meter?

    Klaus
    First of all my apologies for not making the post clearer, the picture above is the block diagram of the suggested IRM-20-12 module ( it's all in there ).

    I'll admit i'm aiming too high as in terms of power budget. My aim was to maybe have a wide supply for the first prototype and then surely the supply will go down since i dont really have the power budget pinned down.



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    Re: 3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applica

    I do not see how it can be done in a simple way; you will certainly need 3 nos 1W 480V 12V transformers. The outputs can be paralleled via a diode.

    You may find it difficult to get 480V transformers. You can use 240V IP and 12V OP transformers and use the input side in series to get 480V. By the way, 480V is Line to Neutral voltage???

    Use varistor for all the transformer inputs. As long as one phase is active, your output will be there...

    I am sure it can be simplified but I cannot see how right now...



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    Re: 3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applica

    Simple 3 diodes, one on each phase will assure power and redundancy for up 2 lost phases.
    After these add caps/ filter and a flyback topology power supply. For such small power and increased redundancy may have 2 such diodes blocks and 2 power supplies, togheter connected by diodes.



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    Re: 3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applica

    Meanwell IRM-20-12 is specified to work up to 305 VAC / 430 VDC, so it can be supplied by suggested 3-phase half-wave rectifier. Disadvantage is that the meter won't work with disconnected neutral.



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    Re: 3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applica

    Quote Originally Posted by c_mitra View Post
    I do not see how it can be done in a simple way; you will certainly need 3 nos 1W 480V 12V transformers. The outputs can be paralleled via a diode.

    You may find it difficult to get 480V transformers. You can use 240V IP and 12V OP transformers and use the input side in series to get 480V. By the way, 480V is Line to Neutral voltage???

    ..
    Most likely it is a line to line voltage, where the line to neutral voltage will be 277 volt AC. These transformers or SMPS are more readily available, at least on this side of the pond.

    Perhaps the OP requires that the meter to be powered from all three phases for redundancy. If one phase goes into brownout or blackout, the remaining phases will still operate the circuit correctly.......Is that the case?
    My batteries are recharged by "Helpful Post" ratings.
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    Re: 3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applica

    To do this properly you need to rectify the 3 phases ( and the neutral - so 8 diodes ) and then use a flyback to generate the isolated 12V ( or whatever ) the flyback mosfet must be 1200V because 3 phase mains has lots of spikes over the life of a meter ...

    POwer integrations has some good suggestions


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    Re: 3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applica

    Quote Originally Posted by Easy peasy View Post
    To do this properly you need to rectify the 3 phases ( and the neutral - so 8 diodes ) and then use a flyback to generate the isolated 12V ( or whatever ) the flyback mosfet must be 1200V because 3 phase mains has lots of spikes over the life of a meter ...

    POwer integrations has some good suggestions
    Agreed, that is what i have in mind for the actual design.

    Quote Originally Posted by schmitt trigger View Post
    Most likely it is a line to line voltage, where the line to neutral voltage will be 277 volt AC. These transformers or SMPS are more readily available, at least on this side of the pond.

    Perhaps the OP requires that the meter to be powered from all three phases for redundancy. If one phase goes into brownout or blackout, the remaining phases will still operate the circuit correctly.......Is that the case?
    Correct, that is the case .

    Quote Originally Posted by FvM View Post
    Meanwell IRM-20-12 is specified to work up to 305 VAC / 430 VDC, so it can be supplied by suggested 3-phase half-wave rectifier. Disadvantage is that the meter won't work with disconnected neutral.
    Noted



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