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ADE7953 vrms is dropping with increase in load

Hello,

Referring to my previous post https://ez.analog.com/energy-metering/f/q-a/110709/ade7953-not-giving-accuracy-after-calibration i am asking this question 


1. while testing i encountered a situation where my vrms voltage is dropping while increase in load.


At 200 watt,0.75 amp load i am getting vrms = 245volt.

At 400 watt, 1.5 amp load vrms = 243 volts,

At 600 watt, 2.25 amp load vrms = 240.5 volts.

At 800 watt, 3 amp load vrms = 238 volts.

At 1600 watt, 6 amp load vrms = 227 volts.

VRMS Raw values at 200 watt load             VRMS Raw values at 400 watt load
5815980,                                                       5793771,
,5820501,                                                    ,5799628,
,5812244,                                                    ,5798432,
,5813605,                                                     ,5797601,
,5813961,                                                    ,5794260,
,5820619,                                                    ,5796468,

VRMS Raw values at 600 watt load           VRMS Raw values at 800 watt load
,5749087,                                                   5700229,
,5750694,                                                  ,5702440,
,5752725,                                                  ,5696510,
,5754846,                                                  ,5692546,
,5749377,                                                  ,5695442,
,5750760,                                                  ,5696431,
,5702863,

VRMS Raw values at 1000 watt load        VRMS Raw values at 1600 watt load
5660079,                                                   5560185,
,5664626,                                                 ,5572938,
,5664523,                                                 ,5576138,
,5672046,                                                ,5571190,
,5673604,                                                ,5576863,
,5669041,                                                ,5569819,
,5666732,


what can be the reason for this?

2. We have designed the hardware as per the test circuit given in the ADE7953 datasheet, just instead of CT we have used shunt of 5 milli ohms. can it be a hardware issue?

Please suggest possible solution for this.

Thank you,

Regards,

Akshaay

  • Hi akkshay,

    Apologies, i haven't replied to your previous question in the other post.

    1. Can you try measuring the voltage RMS using another meter. I suspect this is not due to the ADE7953 chip giving incorrect measurement, because even though calibration is bad, it will not give a very large error as much as the data provided above. The ADE's role is just to measure what is the actual. If the voltage is dropping due to load, it might be not because of the metrology chip but the power system. So I suspect this is not a metrology issue but power system issue. We can verify this by using a reference meter or you can probe even a simple voltmeter and see if there is a drop in the line.

    2.  No, it is okay to use a shunt for as long as you have designed the AFE properly, can you send the schematic to us?

    Thank you very much.

  • Hi aheredia,

    1. I tried measuring the VRMS voltage using other ade7953 chip but got same result. When i supply the load via ade7953 and connected a reference meter(of MECO brand) at load side there was same voltage drop showing in reference meter.
    But when i connected the load directly to supply then there was no voltage drop measured on reference meter even if i increased the load. so, according to my understanding there must be some issue in ade7953 hardware side.

    Thank you.

  • Dear aheredia,

    PFA the schematic that we have used, here we have connected shunt resistor of 5mOhm across the relay and 2 twisted wires from Shunt than go for measurement to the ADE at the points shown in the schematic.

    PDF

    Also, we have seen that the voltage drop majorly occurs due to the shunt resistor.

    Could there be any reason for this?

    We have calculated the shunt resistor so that we can use it up to 20Amp Load. Is this fine?

    Regards,

    Ajit Wadekar

  • Hi guys, how are you connecting the load to the system?

    According to the label you are putting the load across the shunt resistor?

    Can you please clarify?

    The load is placed across the phase and the neutral.

  • Dear aheredia,

    We have connected the Load in series with Shunt Resistor i.e load is in between Phase and Neutral with shunt resistor in series.

    And we are measuring the voltage across shunt resistor  for current parameters and

    For voltage, we have directly connected phase and neutral to AC supply points as shown in the schematic

    If you have any queries related to this, can you specify the question, would be easier for us to help you understand it.

    Regards,

    Ajit Wadekar

  • Hi ajit,

    Thank you for the response. Hoping we solve this sooner.

    OK I will have few questions and some clarifications:

    1. It is correct that you connect the load between the LIVE and NEUTRAL of course and generally correct that he shunt is in series BUT make sure that your shunt grounding reference is in proper place (the correct shunt grounding to the meter should be in the PHASE after LIVE OUT or after Shunt but before the load)

    2. Where in the system are you putting or inserting the shunt? is it in the live or is it in the neutral?

    3. I saw in the schematic diagram that your reference grounding to the meter is in the neutral. Is this correct?

    4. Can you share to us your system diagram connection for a review?

    Thank you very much.

  • Dear aheredia,

    I am attaching here the block diagram of the complete system, I think this should clarify all your doubts.

    PDF

    Regards,

    Ajit Wadekar

  • HI Ajit, may I know what power supply did you use? Did you use an isolated PSU? Also the supply and grounding of the controller, it seems to be on the Hot side and not on the safe side, though this is different from the loading issue.

  • Dear

    We have used a Non Isolated Power Supply, because of our use Case.

    And yes we have connected it accross the Hot Side again because of the limitation that we have on our system.

  • Hi Dave can you comment on their power supply? Should it affect?