Michael Cunningham wrote: > On Sun, Mar 9, 2008 at 5:20 AM, piclist wrote: > >> I'm currently doing (or attempting to do!) much the same thing using one >> of these: >> >> http://www.crmagnetics.com/pdf/3110.pdf >> > > Very cool.. looks like a good solution. Do you run the entire ac line > hot/neutral/ground through the unit or just the hot? I like that it doesnt > splice into the wire. It has a 0.40" opening for the wire. If you just run > the hot through doesnt the extra space for it to move around change > the reading? Ie varies the strengrth of the detected magnetic field? > > You have to hook it round just one, either phase or neutral, otherwise the pair will cancel each other out. I bought a $3, 1 meter three-core extension cable and split it with a hobby knife, since the meter box (where this thing is going to end up!) is too far away and outside... I haven't tried moving the cable round to see if there's any effect - I assume there would be, but have no idea how much. Since the readings are so close, I probably won't bother - if need higher accuracy, you might have to investigate... > How acurate is it? > I have a linear response (based on 3 data points!) which closely mirrors the readings from the NZD20 "appliance meter" I bought locally - my CR3110 reads slightly low, but it's off by around 20W/1000, which is good enough for my purposes... Admittedly, I do have a non-linear region at the bottom end (<150W - one/two lightbulbs!), but I can live with that. It may be something to do with the bridge (4*4004's), but I haven't investigated too much yet - the forum suggests that this shouldn't be the cause, though. > Is this true? > > "When you convert a AC to DC by a full wave rectifier > bridge you have to multiply the output voltage by 1.41 > to obtain the VA" > > I kind of ignored that bit of the discussion since I got pretty close to the bought meter without it. However, I just consulted my (20-year-old) university text (electronics was not my major!) and it seems that the 1.4*output gives the peak voltage suffered by the bridge, so I guess it should be used to determine the diode spec? (I think my 4004's are way over spec'd, if that's the case!) But I'm sure some of the Great Experienced Minds here will have something to say (please?) :) Andrew -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist