Kill A Watt P4400 on sale
in [Repair]
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From: David Nebenzahl on 5 Sep 2009 15:09 On 9/5/2009 11:50 AM Jeff Liebermann spake thus: > On Sat, 05 Sep 2009 13:11:29 -0400, "Michael A. Terrell" > <mike.terrell(a)earthlink.net> wrote: > >> It is an inline device: >><http://www.p3international.com/products/special/P4400/P4400-CE.html> > > Some more... > > Photo of the insides of the original and the later P4440 versions. The > P4440 is at the bottom: > <http://802.11junk.com/jeffl/pics/drivel/slides/kill-a-watt.html> So how does this thing work? It looks like the power just passes straight through from plug to socket over there on the left. Is there a current transformer in there somewhere? What about that half-loop thingy on top? And what's that semicircular thing doing between the power prongs above the ground connector? -- Found--the gene that causes belief in genetic determinism
From: William Sommerwerck on 5 Sep 2009 15:29 >> When I get around to it, I'm going to put it on my fridge for a few >> days. I want to see exactly how many kWh it draws over a week or so. >> You can't do that with a clip-on, because refrigerators run intermittently. > That's true - but what action will you take? You can hardly switch it off > to save energy. Unlike heating and aircon. If it's old a new one will > almost certainly be more efficient. But may cost more than it saves. Correct. But I feel my electric bill is too high, and I need some evidence to argue with the utility. I intend to measure everything in my condo.
From: Jeff Liebermann on 5 Sep 2009 15:37 On Sat, 05 Sep 2009 12:09:18 -0700, David Nebenzahl <nobody(a)but.us.chickens> wrote: >On 9/5/2009 11:50 AM Jeff Liebermann spake thus: > >> On Sat, 05 Sep 2009 13:11:29 -0400, "Michael A. Terrell" >> <mike.terrell(a)earthlink.net> wrote: >> >>> It is an inline device: >>><http://www.p3international.com/products/special/P4400/P4400-CE.html> >> >> Some more... >> >> Photo of the insides of the original and the later P4440 versions. The >> P4440 is at the bottom: >> <http://802.11junk.com/jeffl/pics/drivel/slides/kill-a-watt.html> > >So how does this thing work? It works quite well. The actual device is made by Prodigit in China: <http://www.prodigit.com> <http://www.prodigit.com/index.php?lang=en&op=product&pro_num=1051> <http://www.prodigit.com/index.php?lang=en&op=product&pro_num=1052> >It looks like the power just passes straight through from plug to socket >over there on the left. Is there a current transformer in there >somewhere? I haven't ripped it apart and traced out a schematic (yet). As near as I can guess(tm), the big half loop near the power jack is a low value series resistor. There's no current xformer inside. The big green capacitor is probably AC line coupling for measuring the voltage. The LM324/LM2902 is probably setup as input sections of an instrumentation amplifier to float and isolate the AC line from the rest of the circuitry: <http://en.wikipedia.org/wiki/Instrumentation_amplifier> The chip on the display (right) section is apparently a proprietary ASIC and probably handles some of the analog circuitry, the A/D converters, and display functions. >What about that half-loop thingy on top? Series resistor. >And what's that >semicircular thing doing between the power prongs above the ground >connector? It's part of the plastic case. My guess(tm) is that it's to align the power jack connectors to the case. Since there are no mounting screws, and the PCB is attached to the case with hot melt glue, something like that is required. No clue why the strange shape as some round holes would have done as well. My guess(tm) is that if one of the brass power jacks became detached from the PCB, it would not lean into the opposing connector as it is blocked by the plastic thing. -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
From: Jeff Liebermann on 5 Sep 2009 16:07 On Sat, 5 Sep 2009 11:11:09 -0700, "William Sommerwerck" <grizzledgeezer(a)comcast.net> wrote: >> Those can be fine, accuracy-wise. But of very limited use. After >> all, it's not difficult to work out what most appliances cost to run. > >When I get around to it, I'm going to put it on my fridge for a few days. I >want to see exactly how many kWh it draws over a week or so. You can't do >that with a clip-on, because refrigerators run intermittently. Yes you can with the proper adapter. <http://support.radioshack.com/support_meters/doc21/21584.htm> The Radio Shock inline current sensor is the device on the right. It's normally NOT sold seperately. It consists of 1 turn and 10 turn loops inside a plastic case, wired in series with the AC line. The clamp-on meter clips into either the 1 turn hole for fairly large currents, or the 10 turn hole for a 10x current multiplier. You could easily build one of these if you can't find one to buy. However, there's a problem. Your fridge is an inductive load, which will require power factor correction to obtain the same current as measured by the typical disc type electric power meter. You can't do that with a typical clamp-on ammeter. You can do that with a wall mounted inline power meter. Also, watch out for refrigerators that have self-defrosters. Some are on demand, while others are on a timer. The defroster sucks LOTS of power and will be a big part of the electric bill. Same with on-demand ice cube makers. -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
From: David Nebenzahl on 5 Sep 2009 16:18
On 9/5/2009 12:37 PM Jeff Liebermann spake thus: > On Sat, 05 Sep 2009 12:09:18 -0700, David Nebenzahl > <nobody(a)but.us.chickens> wrote: > >> So how does this thing work? >> >> It looks like the power just passes straight through from plug to >> socket over there on the left. Is there a current transformer in >> there somewhere? > > I haven't ripped it apart and traced out a schematic (yet). As near > as I can guess(tm), the big half loop near the power jack is a low > value series resistor. Ah, so. So the loop must be connected on one side to the incoming hot line, and on the other side to the outgoing hot line. Then the unit measures the voltage across the loop (resistor) proportional to current. Right? -- Found--the gene that causes belief in genetic determinism |