Summary: Kill-a-Watt P4400 / P4460 circuit diagram here: http://bit.ly/killawattp4400 1. Replacing the current shunt in the Killawatt with 2 x 0.1 Ohm, 1% 1/4 Watt resistors in parallel should make it 10 x more sensitive and better usable with low loads. (My wanderings below suggest that the meter thatv the circuit referenced below relates to is 10A, 230V rated with a 5 milliOhm shunt.) 2. Replacing Rsense with a CT with a suitable burden resistor to give 2Vrms at max desired rated current should allow it to be used with the circuit in refence with burden R being changed as desired to get lower power operation. There are numerous low cost CTs available which should allow this. _______________________ You should be able to modify your P4400 Killawatt with relative ease [tm] to allow it to be more useful at low power levels. A possibly correct (looks OK at a glance) circuit diagram of the P4400 / P4600 Kill-a-Watt is here http://2.bp.blogspot.com/-jxGvzdj4ykQ/UU2u8sAZy5I/AAAAAAAAAJI/r0q3BQoRIqU/s= 1600/KAW_LV.JPG =3D http://bit.ly/killawattp4400 U3D appears to be the voltage monitor (gain of ~ 10k/1M =3D 0.01) and U3A + U3C the current shunt monitor (gain of 100k/2k55 x 1M/100K =3D 392) To provide greter sensivity you can increase current channel gain or increase the current shunt resistance. (I assume this works with a shunt rather than a CT but maybe not. ) Vdd iis 5V (U5) and Vref for the amplifiers is 2.33V (5V x R12 / (R12+R27) So say 1.5V RMS swing max. So V_Isnese max =3D 1.5/392 =3D 3.8 mV. For I max =3D 10A, Rshunt =3D V/I =3D 3.8mV/10A =3D 0.00038 Ohm. Rather low. NO!!! I had another look nd saw that the current amplifier's two gain stages boith feed the procesor. So gain for current =3D 39.21 OR 392.1 ie they have a low and high current setting - so have already done what I was suggesting :-). At gain =3D 39.21, for 2V RMS to uP, Vshunt =3D 50 mV. So 5 milliOhm at 10A or 2.5 milliOhm at 20A. Assume 10A max. On low I setting you get 2 Vrms at uP for 1A load current. That SHOULD easily allow half OK accuracy at the 10 mA range or 2. Watts on 230 VAC. Increasing Rshunt to 50 milliOhms (assuming the above is correct) decreases meter Imax to 1A and SHOULD make very low current loads reasonably mesureable. Using eg 2 x 1%, 0.1 Ohm in parallel. At 1A max or 500 mA/resistor power per R is 0.5^2 x 0.1 =3D 0.025W. At 10A max that rises to 2.5W/resistor so you may not wish to use a modified meter at 10A :-). CT: Use of a current transformer in place of the assumed sense resistor above would allow easy safish changing of sensitivity. Note that most small energy meters use "real" energy meter ICs which are essentially the same functionally as used in commercial energy meters. I have seen DS5460 / DS5461 ICs (& others) in meters sold here. ________________ *Files on my disk. Will put on dropbox after a reboot:* Microchip MCP39F501 DS CS5460A from CL site - energy meter IC as per Jaycar MS6115 energy meter www.cirrus.com_en_pubs_proDatasheet_CS5460A_F5.pdf DS Energy Meter IC Cirrus Logic CS5490 - highly capable - _Q96 - _ERGE www.cirrus.com_en_pubs_proDatasheet_CS5490_F3.pdf DS Energy Meter IC uChip MCP3909 nice to use _q95 ww1.microchip.com_downloads_en_DeviceDoc_22025C.pdf DS Energy Meter like CS5460 in Jaycar MS6115 energy meter CS5461 pdf, CS5461 description, CS5461 datasheets, CS5461 view ALLDATASHEET .htm= l DS Energy Meter like CS5460 in Jaycar MS6115 energy meter CS5461 pdf, CS5461 description, CS5461 datasheets, CS5461 view ALLDATASHEET _files DS Energy Power meter IC superb _Q96 Microchip MCP39F501 Digikey pricing page - onchip rms power calc & v & I - serial async bidi interface ww1.microchip.com_downloads_en_DeviceDoc_20005256A.pdf DS Energy Power meter IC superb _Q96 Microchip MCP39F501 onchip rms power calc & v & I - serial async bidi interface ww1.microchip.com_downloads_en_DeviceDoc_20005256A.pdf DS Maxim 78M6610+PSU energy meter IC - 20 page design guidelines excellent _q95 July 2012 pdfserv.maximintegrated.com_en_an_UG5475.pdf DS Maxim 78M6610+PSU energy meter IC - excellent _q95 datasheets.maximintegrated.com_en_ds_78M6610+PSU.pdf DS notes CS5460a PINOUT ENERGy METER.jpg On 26 November 2016 at 16:57, Art wrote: > I have a Landis & Gyr E350 FOCUS AX-SD smart meter that I'd like to use > to do some work on power factor correction-namely, how to inexpensively > improve the power factor for LED light bulbs. They have outrageously > poor power factors, if the utilities begin billing for reactive power..I > think there might be a move back to incandescent lighting::> > > I got a neat little portable power meter called the Kill-a-Watt (model > P4400) from my local library, and already found some big power suckers > in the house! But it's pretty crude, especially for low power things > like LED lights and it fails miserably at measuring standby power levels. > > But, I'd like to access the Landis & Gyr smart meter to get more > detailed information from it and to continue research into power factor > correction for these new fangled LED bulbs. > > I did obtain the manual for the smart meter, despite the manufacturers > best efforts to deny me a copy::> It has an optical port that can be > accessed without taking the cover off the meter, which makes it ideal > for me. But, the manufacturer will not share any of the details on the > software or hardware needed to extract the data I need from the optical > port. The optical port is an "ANSI C12.18 type optical port". I did > figure out that the optical interface/computer cable can be bought for > reasonable $$. > > I also thought about building an interface to a computer sound card, > which isn't a big deal technically, but I am not sure I could handle the > software to extract the real time data from the voltage and current > transformers output. But, sampling at 48K (or higher) would yield some > nice high resolution V/A plots! > > Has anyone here hacked one of these smart meters or have any experience > with them?? Email me off-list if you do not want to make a public respons= e. > > GL. > > Art > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .