watt meter

[MrRao]

hello guys,

i'm trying to build a circuit for calculating kwh for a dc application. can anyone help me how to build in labview , share vi if possible 

[Bob_Schor]

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?@MrRao wrote:

hello guys,

i'm trying to build a circuit for calculating kwh for a dc application. can anyone help me how to build in labview , share vi if possible 

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• Not all Forum participants are "guys".
• I'm not an engineer, but even I could build such a circuit (it might not be "ideal", and a good EE would probably sneer, but it should work ...)
• Why don't you put in a little effort, design the circuit, and you "share" it with us?  Why should we "do your work" for you?

Bob Schor

[MrRao]

I'm sorry for not sharing the VI screen. here i attached the VI Screen. let me know is it correct? or need to be changed.

Thanks.

   

[RTSLVU]

Wh meter for DC power

Well the basic formula you are using is about as good as you can do without an actual wattmeter with Ah integration. (Watts/time)

What exactly is your issue?

[RavensFan]

I don't see where you are doing any accumulation of the watts.  You are just taking the current power and multiplying it the amount of time the program has been running.

So if you had 1 kW the first hour, 2 kW the 2nd hour, 3 kW the 3rd hour, you would have used 6 kWH.    But your VI takes the latest value of kW (3) and multiplies it by 3 hours making it look like 9 kWh.

You probably want a shift register to accumulate your watts as you read them.

[RTSLVU]

Ravens Fan brings up a good point... I missed that. 

Also doing it this way you have to make a certain amount of assumptions 

The biggest being that you have to assume that your power is going to remain constant between measurement intervals. 

Depending on your source, load, and sample rate this may or may not be constant. Having done a comparison when charging a battery between calculating Ah [(V*I)/t] and actual Wh integration there was as much as a %20 difference due to the "constant power" assumption at one second intervals.

[RTSLVU]

But for what it's worth, we decided that calculating was close enough for this one project and here is how I did it.

I just realized that this was calculating Amp Hours not Watt Hours...

Well it's basically the same thing (not really) but Wh = (V*I)/t instead of just I/t

[MrRao]

i need to find the power consumption used by the load, where consumption should be in kwh units, in this case current is not constant its varies, and what ever the value kwh is displayed in labview that should be matched with watt meter i'm using G.T. Power RC Watt for comparing with labview measurements.

 

[MrRao]

Is this method your trying tell me to do, please check it , and let me know, or should i take amp/hrs then multiply with load Voltage to get the watt/h. is it so let me know how to implement 

Note: Current is not constant. 

[MrRao]

can u explain me how did you got time in hrs.