road-runner wrote:
Gdetrailer wrote:
The cleanliness and accuracy of the generator WAVEFORM also plays a key roll in just how accurate your "Killowatt" meter will end up.. Poor quality sine waves OR Modified Sine waves do not "play well" with the Killowatt meter..
My observation has been different, finding that the kill-a-watt gives reasonably accurate RMS values with MSW and mangled sine waves. The only shortcoming I found with MSW is that the frequency reading doesn't work.
Kill-A-Watt is a HOMEOWNER type of device, it is not "held" to strict "standards".
From a average "Home owner" type of need, it is OK, gives a readout of voltage, amps, power, VA and frequency and does what is "advertised" to do.
It was however never designed nor advertised to be used in "mission critical" applications to which I would place BFL13's current "mission".
It does have known issues with accuracy.
https://forums.anandtech.com/threads/kill-a-watt-power-meter-accuracy.137169/For those too lazy to go to that website, I will quote a few snips of it.. Quotes from that website in Italics..
"I had a friend over today that wanted to show me his new purchase, a fluke 1735 , so I thought I would do a quick comparison with the killawatt.
The killawatt isn't a bad meter, especially for the price.
Its does have its flaws though.
Comparing it with a fluke 1735 I found a few differences.
The killawatt is terrible at inductive loads, so don't use it for measuring those.
Inductive loads would be things typically with motors, compressors.
So not good for measuring a refirgertator or washing machine.
It measures them , but its results are not .2% accurate.
Refrigerator with compressor running 921 watts, fluke 841.8 watts
Its not accurate at measurements of small wattages.
Things like the power usage of a dvd player in standby mode are not accurate.
Killawatt said dvd player was using about 5 watts, fluke 2.64 watts.
The sampling rate is very low compared to meters like the fluke, so it can miss quick spikes or surges in usage . When I used it to measure the power usage of a 51" hdtv at turn on, it constantly gave different readings. Range from 410 watts to 504 watts. Fluke 448 to 453 watts.
PC, using a 750watt Ultra lsp model.
Core2, running at 3.3ghz, 7900gtx , pc running gelato (nvidia software that uses the gpu as a fpu, while also using the host cpu), maxes both.
Killawatt 316watts, fluke 329watts.
All that said its still a good device to use.
Its not as good as some of the professional tools like the fluke 1735, but then the fluke meter is over $2000 while the killawatt is less than 20.00"Next..
"I recall the issue as being 100% efficiency, not greater than, and it only happens sometimes with APFC units."(APFC is Active Power Factor Correction by the way)..
Next (my favorite AND applies to the average Kill-A-Watt owner)..
"Unfortunately, most people believe it is accurate all the time "Don't get me wrong, for the price it is OK and it will get you ballpark numbers but as a dead on 100% correct measurement device it is not and never was meant to be and never will be.
Additionally the OP is trying to use this with a low cost "inverter" low wattage inverter generator.. The waveform of said generator may or may not be 100% pure sinewave at the load level that the OP is presenting which can and does effect the final numbers the Kill-a-watt may deliver.
One does need to understand that just because it is an "inverter" gen it MAY NOT have 100% perfect sinewave. This is highly dependent on how much "fudge factor" may be built into the generator.
Starting with the high frequency alternator which must support the load to the DC rectification AND FILTERING to high voltage DC of the high frequency alternator output, then to the chopper circuit of the inverter which converts the rectified high voltage DC to PWM (pulse Width Modulated) waveforms that form the final and hopefully sine wave output. Not ALL inverters (including GENERATOR BASED INVERTER MODULES) are able to handle ALL loads 100% the same way regardless of reactive, non reactive.
OP also needs to check the wave form under the test conditions, that also means a pretty decent Oscope that has sufficient bandwidth to SEE any spikes in the waveform and even perhaps good enough to see the PWM noise in the output..