Kill-A-Watt Schematic

[ianmcm]

I was thinking of modifying a Kill-a-Watt to do stand-alone (no PC required or scope required) power measurements on general AC circuits (not just 110V and not just 60 Hz). Having a schematic of the kill-a-watt would save me some time tracing it. Does anyone know if one is available?

[johngineer]

I was thinking of modifying a Kill-a-Watt to do stand-alone (no PC required or scope required) power measurements on general AC circuits (not just 110V and not just 60 Hz). Having a schematic of the kill-a-watt would save me some time tracing it. Does anyone know if one is available?

I doubt it. The Kill-A-Watt is a proprietary consumer product, so it's unlikely there are schematics available.

What do you mean by "power measurements on general AC circuits"? Do you mean on things like audio signals from an amplifier?

I'm asking because "AC" is a big category, and the Kill-A-Watt probably wouldn't be practical for many AC signals (without significant modification of the circuit). For example, if it uses a bridge rectifier with diode drops of 0.7v, that's not a big deal when you're looking at 110v, but significant when dealing with a signal of 1v amplitude.

[ianmcm]

See my reply as a new thread in the XBee topic. I meant to post there originally, since the Kill-a-Watt was used in the Tweet-a-Watt XBee project, but I accidently posted here.

[AJOT]

KillAWatt circuit schematic diagram (approximate), and calibration procedure (no guarantee), for model P4400, are posted at:

https://picasaweb.google.com/115515825869141953416/KillAWattCircuitSchematicDiagramCalibrationProcedureModelP4400#

NOTE: In the circuit schematic, LT IC's are substituted in the diagram for the actual IC parts, in order to use LTSpiceIV.

...This information is not guaranteed to be accurate.

Out of curiosity, what does the Kill A Watt do when you test the inverter?

[adafruit]

handy!!!

[oPossum]

I made schematics of the KAW a while ago while working on a serial interface for the KAW. The schematics where not made public for fear it would encourage someone to do something stupid.

There are four generations of the KAW (that I know of). The second, third and fourth generation are the same circuit with a different PCB. Each newer generation uses more SMD parts. The first generation is a somewhat different circuit, but functionally mostly the same. The standard KAW (P4400) and the EZ (P4460) version differ only in the microcontroller firmware or possibly just some data stored in the EEPROM - the circuits are identical.

EAGLE and PDF schematics of generation 3 Kill-A-Watt.

I also have done generation 1 on paper, but have not had time to draw it in CAD. The schematic posted by AJOT is for generation 1, but does not show some components (most of the missing components are usually not populated on the PCB).

[AJOT]

oPossum, Thank you for your post.

The schematics I posted are for the P4400.

The schematics include all of the populated parts in this model, none are omitted, except the AC connectors are not explicitly shown.

LTSpiceIV was used for the analog schematic. LT semiconductors were substituted in order to run the simulation. Therefore, I omitted the semiconductor part numbers from the printout.

The AC input is shown as a sine source and a noise source. The load components are labeled DUT, again, for the sake of simulation.

The schematic is organized to render the sense of the circuit at a glance, and it is also organized for easy troubleshooting, which was my motive.

By the way, in troubleshooting, all of the signals looked normal. The unit had lost its calibration somehow, apparently from a noisy load. I have also posted the steps used to re-calibrate it.

oPossum, in your schematics, do the reference designators match your boards? I ask, because your designators are different from mine, and mine do match my boards.

I also have photos of the boards that I used for tracing the schematics (not posted).