MarkT is correct with the CT however it has an isolated AC output which you will have to convert to DC and filter for a current measurement. The low pass filter is the critical factor in the design, it controls the accuracy and response time. If you got time no problem. The voltage is easy if connected properly and is also isolated from the mains. Use a step down transformer with the primary connected to the mains and the secondary is for the arduino, same filtering etc as the CT circuit but different levels. In my area my wire insulation on the secondary has to be equal to or greater then the primary insulation rating. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
The breakdown voltage for air is 3 million volts per meter , or 3000 V/ per mm, so if the mfg says its rated for 297 V I don't see any reason not to believe it . It would take 300V to arc 0.3 mm so I' sure there's more than enough clearance for isolation.
raschemmel:
The breakdown voltage for air is 3 million volts per meter , or 3000 V/ per mm, so if the mfg says its rated for 297 V I don't see any reason not to believe it . It would take 300V to arc 0.3 mm so I' sure there's more than enough clearance for isolation.
And how much would it be with condensation on a dirty PCB.
I don't see any milled slot in that Sparkfun board.
Tinkerers in the US can be less concerned with 120volt AC.
Leo..
Are you serious??? First of all, that device measures DC current, not AC. Secondly and much more importantly, there is nowhere near enough isolation to safely separate 230V mains from a 5 volt DC circuit. At best, this idea will just produce a lot of smoke, at worst..... well need I say it?
Wawa:
And how much would it be with condensation on a dirty PCB.
I don't see any milled slot in that Sparkfun board.
Tinkerers in the US can be less concerned with 120volt AC.
Leo..
Agreed. I am in the US (120v mains) and NO WAY would I use that little board connected to the AC line. It would be a disaster waiting to happen (even if it DID measure AC current.. which it does not).
It says 'Galvanically Isolated" . It also says for 'low current ' applications. I wouldn't run if it got wet and I would probably clean it with IPA first and put it in a metal box, but given that, yeah I don't see a problem with it. I wholeheartedly agree that no weekend hobbyist should mess with mains voltage all , for any reason but we've always had posters who couldn't be convinced that there is a "thin red
line" they shouldn't cross but if we accept that this guy is one of those and he's smart enough
to clean it with IPA and seal it in a metal box with silicone sealer to keep out moisture, I don't see 220V as a problem with the distance bewteen those two large round holes on the board for the AC connection. I worked with 277Vrms on a daily basis for 4 years. The product was designed for 240rms but we tested everything at 277V on general principals. I'm not worried about the pcb or the IC. Personally I would never even consider using such a product. A CT or clamp on current probe is the way to go. I'm a big fan of CT's because I've used them before (theyre not expensive either. I have one on my desk at work that is perfect for this application.) I used the (Tek A621) current probe every day for 4 years. The only reason I didn't suggest that is because then the OP is in the loop for all the wiring and circuitry from the CT on. With the Sparkfun board , it's plug & play to the arduino. I would be more worried about the OP not realizing current is measured in series. If I had access to 220V I would test one of them but I would never use one because there's no surge protection. (technically I could
test it with the 220V outlet at work but I don't test personal projects at work on general principles
(the company insurance doesn't allow for that. It's a terminable offense. With they hire someone with
my experience they expect me to know better than to break the rules)
There's no guarantee that the mains will never exceed 220V. With a CT you don't even have to think about that. I'll post the part number for the CT I have at work tomorrow. It one of these (but I don't remember the part #).
I agree CT is the first choice but then all the rest of the wiring and circuit has to be perfect. With the ACS723, if you're willing to risk a the possibilty of a surge, all the heavy lifting is already done and you just connect it to the arduino like any orher breakout board. If all we're talking about is whether or not the sparkfun board would work if I used it in a sealed metal or plastic box then I say it would work until a surge exceeded the rated 297V. That gap is more than enough for 220V. I know that for a fact from 4 years of ecperience working with 277V and the ACS723 is galvanically isolated. Do I think a hobbyist should use one ? That's their call but I stand on the board will work. (for 220V) If the OP can be trusted to do any wiring then I vote for the CT approach, but the 'weak link' here is the OP , not the ACS723 (except for the surge case).
RTFM !!!!!!
It DOES measure AC.
You want me to post where it says that ?
"The SparkFun Current Sensor Breakout is a high accuracy board that utilizes the ACS723 for moderate AC and DC "
900
CORRECT ! (thanks for catching that)
3,000,000 "is to" 1 meter
as
x "is to " 0.3mm
cross multiply
x = 900V.
And how much would it be with condensation on a dirty PCB.
I don't see any milled slot in that Sparkfun board.
That's not the manufacture's fault. Clean the board with IPA and seal it in a box and then that
comment goes away. Let's not even get into the "Should tinkerer's mess with mains AC ?" debate
because there's only one answer to that and not all posters agree about it.
With freedom, comes risks. Is telling someone not to do something enough ?
If they never post again you have your answer.
krupski:
...(even if it DID measure AC current.. which it does not).
A CT must be biased mid-voltage, and the the AC current sinewave must be sampled many times to get the shape or peak of the wave.
Same difference with a bipolar ACS712/723, except that the biasing is already done for you (idle out = VCC/2).
Not a problem to measure AC with these chips.
Leo..
I checked DigiKey just now. The -AB suffix parts do AC and DC. I stand corrected. However, in my defense, only "ACS723" was mentioned. I've used these before, but only the DC parts and I never noticed that there was also an AC version.
Wawa:
A CT must be biased mid-voltage, and the the AC current sinewave must be sampled many times to get the shape or peak of the wave.
Same difference with a bipolar ACS712/723, except that the biasing is already done for you (idle out = VCC/2).
Not a problem to measure AC with these chips.
Leo..
A CT requires a "burden" (a load resistor). The AC voltage across the burden can be rectified and filtered, then fed to an ADC.
There will be a small intercept error at low currents (where the diode is just beginning to conduct). A schottky diode or better an op-amp rectifier can minimize this problem.
I still think those little hall effect current sensors are not safe to use directly on the mains. Maybe a CT and an ACS723 together would be ideal.
I might be wrong about it including the burden resistor.
The diagram shows an included resistor DCR (74 ohms for this model) in series .
It also shows a resistor "R" in PARALLEL with the CR. (This must be the BURDEN resistor since it is in
PARALLEL) but no value is given for this.
For this part:
Ir = 200 (this is the MAX CURRENT SPEC)
VmaxRMS = 11.5
Te = 2011
DCR = 74
Frequency(f) = 20Hz - 1 kHz
R = UNKNOWN
Which yields :
Let Ir = 200 (for example purposes)
krupski:
I never noticed that there was also an AC version.
The bi-directional version is common (± DC and AC). The uni-directional one is not.
krupski:
A CT requires a "burden" (a load resistor). The AC voltage across the burden can be rectified and filtered, then fed to an ADC...
But it's usually not done like that, because of that diode threshold.
The AC signal is usually presented mid-voltage to the analogue pin, and peak/peak value is extracted by continuous sampling at least 3/4 of the sine wave.
Leo..
