Hi,
I have built a monitor, which seems to be working well. I have however noticed a linkage between current and voltage - for example, when I turn on my electric shower, the measured voltage drops considerably.
My first thought was that this might be real - more current, volt drop etc, but analysis with a scope seems to suggest this is not so.
Interestingly though, the arduino does seem very sensitive to the 5v level. I have two sources I can use for my 5v supply, on the scope both seem pretty stable and noise free, but powering the board from them can give voltage readings from the 9v wall wart that vary by 10 Vrms. Iwonder whether adding a filter to the AVref pin, as suggested in the uC design notes, might help...
My voltage readings stay in the rang from between 240-250Vrms, but this is a lot more than my scope would suggest.
Has anyone else come across this, or are others voltage logs relatively smooth?
My logged voltage variations can be seen here:
http://bbarker.co.uk/energy/history.php?type=v&from=1440
Cheers,
Ben
Re: Interference between voltage and current readings on ADC
Hello Ben,
I am also experiencing a similar behaviour, when I have a heavy load On the voltage drops down considerably. I think the current adc input is affecting the voltage readings.
I had a similar situation in a different project and I can't remember what I did to overcome this... once I check, I'll revert back.
Good day
Geoffrey
Re: Interference between voltage and current readings on ADC
There seems to be some suggestion on the web that the internal Vref for the arduino ADC is not that stable - I've just tried wiring it directly to my 5v line (having first set the ref as external in the code), and added a decoupling cap. I'll leave it for a few hours and see if it makes any difference :-)
Re: Interference between voltage and current readings on ADC
Hi,
I had some similar problems with a cheap arduino clone, but the UNO was much better. Interferences within the PCB itself are much less than the cheap arduino clone.
I reduced these interferences further by putting a big resistor on the unused analog inputs and grounding them. The best would be to ground properly one analog input between your Current Analog I and your Voltage Analog I.
By the way, a voltage drop is nurmal, when I switch 2KW loads on, I experience a 2-3v voltage drop. (Germany)
Good luck with debugging ;)
Re: Interference between voltage and current readings on ADC
Well, running my meter is parallel with a professional voltage logger, and it looks like my values are actually reasonably accurate - including the +5v drop when I turn on my shower :-)