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Re: Kill-A-Watt vs. analog wattmeter



Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Steve,

They are somewhat susceptible to conducted RFI, so its best to protect the line cords from the fields caused by the TC. Best to plug directly into the wall and then not have the cord coiled up. Maybe have a line filter between it and the load. Too bad they only go to 15 amps.

Gerry R.

Original poster: Steve Conner <steve@xxxxxxxxxxxx>

Hi all,

A while back I wrote about how I thought
Kill-A-Watt-type wattmeters could give inaccurate
readings when used with SSTCs. I recently found a
Kill-A-Watt type thing for sale in the UK, so I bought
one to test. (Maplin part no. L61AQ, costs 9.99 GBP)

http://www.maplin.co.uk/images/Full/38343i0.jpg

It's made in China by the Prodigit Co. which if I
remember right is the same company responsible for the
original Kill-A-Watt. I opened it and inside was a
microcontroller plus some chip that I guess is an A/D
converter.

I set up the DRSSTC, and ran the mains feed to it
through the Prodigit meter, in series with my old
Crompton Parkinson 2-coil wattmeter. This is totally
air-cored so shouldn't be affected by high crest
factors.

http://www.scopeboy.com/tesla/drsstc/experiment/meterundertest.jpg


I then fired up the coil to a reasonable power and the results were:

Analog meter read "150" which is 750w since you
multiply the reading by 5.

Prodigit meter read 746w, 1140VA, 6A RMS, pf=0.62

The low power factor means that the DRSSTC was drawing
awful peak currents, but the two meters still agreed
well. I conclude that the Prodigit wattmeter sold by
Maplin works fine for Tesla coiling. It also seems to
be fairly resistant to RFI, although I didn't let the
coil arc to ground heavily.


Steve Conner