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### Topic: acs 714 erratic readings (Read 5585 times)previous topic - next topic

#### MarkT

#15
##### Mar 11, 2011, 03:02 am
Quote
Hi. i know that Ac have pulses, but the DC part should
be  continous ?

No, energy is conserved so those AC pulses have to come from / go to the battery or other energy storage device like a capacitor.  Inverters do have capacitors but the bulk of the power is routed to/from the battery (especially when running at full power).  So the DC current will be pulses.

To measure the average DC current you will have to sample at many times the mains frequency and average the readings, or use an analog low-pass filter before the ADC conversion.  Multimeters use integrating ADCs that average over time anyway.
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#### fca

#16
##### Jul 11, 2011, 09:10 pm
HI there i'm back to this project...
I'm measuring the acs714 right (i believe ) but i don't know how to do the watt/meter part...

i get watts doing Amps x Volts   for instant read i gues is ok ...
now how do i know how many times should i read and sum ?
like

if i do this i must read it once each second ? but i will loose measuring between... i bit lost...

Summary:
how do i get a watthour measure reading amps&volts from a dc source... ??

#17
##### Jul 11, 2011, 10:23 pm

To help make things as simple as possible. DC current and voltage simply means that the "polarity" +side and the -side do not change back and forth. The voltage "level" however can very from almost 0 to infinity up and down as long as the polarity stays the same.

AC current and voltage "alternates" +to- and -to+ on the terminals. In the USA the alternation is 60HZ or 3600times per minute. It makes it handy for clocks because of the relation of 60 seconds in a minute.

Mark
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

#### MarkT

#18
##### Jul 12, 2011, 03:02 am

HI there i'm back to this project...
I'm measuring the acs714 right (i believe ) but i don't know how to do the watt/meter part...

i get watts doing Amps x Volts   for instant read i gues is ok ...
now how do i know how many times should i read and sum ?
like

if i do this i must read it once each second ? but i will loose measuring between... i bit lost...

Summary:
how do i get a watthour measure reading amps&volts from a dc source... ??

Read the current and voltage many times per mains cycle (lets say 1000 times a second), computing the instantaneous power from each set of samples.  Sum these samples and scale the result according to the time between samples and you have a value that is the total energy over time.  Sample and reset this value every second and you have measured the average power every second...

If you are only interested in watt-hours, then this is simply the energy (in Joules) divided by 3,600.  For kilowatt-hours divide by 3,600,000
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#### fca

#19
##### Jul 24, 2011, 12:59 amLast Edit: Jul 24, 2011, 06:09 am by fca Reason: 1
Thanks for the info....
My arduino is doing other thinks beside measuring the amps from the acs714, like sensing batt voltage, controlling some relays and outputing to serial the information...
because of this i have some "delays" how can i keep in main loop doing all other stuff and at the same time read "1000/sec" that value ?

ARduino multitasking .. i will have look  on how to accomplish this ... any tip will be useful regards.

Can you please explain better "Sum these samples and scale the result according to the time between samples and you have a value that is the total energy over time" ?

regards.

#### MarkT

#20
##### Jul 28, 2011, 01:48 am
The issue is that mains power is not a pure sine wave(*) so that to measure true power you have to take account of the waveform, hence the desire to sample the waveform that frequently.  If you only want a coarse measure of power you can take short cuts with this.

What I was trying to say is "integrate the product of V and I over unit time to get average power"

(*) in these days where most mains appliances have switching power supplies (even microwave ovens)
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