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

Kastella

New Member
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

  • A fellow user here asked the same question but had a cumbersome solution(3 transformers) and didnt want an isolated supply.

  • 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 ?
120428

  • 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 ?
 
Last edited:

ronsimpson

Well-Known Member
Most Helpful Member
IRM-20-12
What is your line voltage? (what is the output voltage and current)
Yes it will work. You are only getting power form one line not all three. I tried this for a power meter and the end client rejected it because some time one line goes down and they wanted to keep the meter/computer running. So I made a circuit that takes power from L1,L2,L3 and will work if only line is working.

Simple answer is to use a off the shelf, single phase supply.
If you must take power from all there line I can help.
----edited------
Not my circuit but this is close to what I did. The use the "brick" power supply you mentioned there Rload is.
120433
---edited again-----
I need to go to work now. My design included the neutral and could run from only one line if needed. I will try to find it later.
 
Last edited:

Kastella

New Member
What is your line voltage? (what is the output voltage and current)
Yes it will work. You are only getting power form one line not all three. I tried this for a power meter and the end client rejected it because some time one line goes down and they wanted to keep the meter/computer running. So I made a circuit that takes power from L1,L2,L3 and will work if only line is working.

Simple answer is to use a off the shelf, single phase supply.
If you must take power from all there line I can help.
----edited------
Not my circuit but this is close to what I did. The use the "brick" power supply you mentioned there Rload is.
View attachment 120433
---edited again-----
I need to go to work now. My design included the neutral and could run from only one line if needed. I will try to find it later.
A single line with respect to neutral voltage is 240VAC ; 3 Phase rating of 415V . The load (meter system) current is not yet clear but is surely well below 100mA which is alot and i'm sure will eventually be much lower. The output coming from the off the shelf AC-DC module ( IRM-20-12 ) as mentioned above gives out 12VDC. I would really appreciate it , right now i'm in a bad position waiting to give out a proposal.

Regards
Kastella
 

simonbramble

Active Member
I work for ADI, so thanks for looking at our metering devices. Have you tried contacting your local applications support whether directly or through your local distributor? They should be able to get an answer for you.

Methods I would try - look at Power Integrations. They have the offline market sewn up.

You could also look at a capacitor dropper power supply. Put a capacitor in series with the input to the circuit and impedance of the capacitor reduces the voltage to the circuit. Moreover, since a capacitor has very little ESR, only a small amount of power is dissipated in the capacitor. Best put a Zener on the output side of the capacitor just to clamp the output voltage
 

ronsimpson

Well-Known Member
Most Helpful Member
A single line with respect to neutral voltage is 240VAC ; 3 Phase rating of 415V
Here are some things for you to think about.
Some times you only have 3 Phase with no neutral. That can be a problem.
If you always have a neutral then it is easy because almost any supply can live on the 240/120. You can live on any or all phases and neutral.
The 3 phase no neutral is a little hard because almost no common power supply works at 415 volts ac. I have a prototype I built for a metering project using parts from Power Integration.
If I remember right; last I had to build a supply that works from 80v (120 low line) to 440V ac. It would have been easier if the 80 volts was not there. Or easier of the 440 was not there.
IRM-20-12
12V 1.8A 21 watts. Is there a chance you can live with less than 21 watts?

Please find out if neutral is always there. What is the lowest and highest voltages? How much power out of the supply?
 

Kastella

New Member
Here are some things for you to think about.
Some times you only have 3 Phase with no neutral. That can be a problem.
If you always have a neutral then it is easy because almost any supply can live on the 240/120. You can live on any or all phases and neutral.
The 3 phase no neutral is a little hard because almost no common power supply works at 415 volts ac. I have a prototype I built for a metering project using parts from Power Integration.
If I remember right; last I had to build a supply that works from 80v (120 low line) to 440V ac. It would have been easier if the 80 volts was not there. Or easier of the 440 was not there.

12V 1.8A 21 watts. Is there a chance you can live with less than 21 watts?

Please find out if neutral is always there. What is the lowest and highest voltages? How much power out of the supply?
Certainly this module is an overkill in terms of power capacity for the project, power budget is not yet determined but i would guess less than 100mA @ 12V . Neutral will always be installed ofcourse.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
The simplest approach would be three of these, or similar:

Connect one from each live to the neutral for input, connect the 0V outputs together and use a schottky diode from each output to your equipment, so there is no back-feed if any phase is off.

There are other versions that are pin-compatible, eg. https://uk.rs-online.com/web/p/embedded-switch-mode-power-supplies-smps/1812194/

Or even cheaper types, if exposed live components are not a problem:
 

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