# Kill-A-watt usage info?

Discussion in 'Home Power and Microgeneration' started by m II, Feb 12, 2005.

1. ### m IIGuest

Has anyone ever used this thing on some circuit OTHER than 60 hz 120V?
The reason I'm wondering is whether or not it could be used on a small
AC producing wind turbine to show delivered power.

The output may or may not be a good sine wave and the frequency is all
over the place.

Any insights welcome.

mike

2. ### danny bursteinGuest

I crossed my fingers and tried it earlier this week on a 208V circuit [a].
It didn't release any magic smoke, but the readings were unusable.

It told me the voltage was 173 and the frequency was 120. That's just so
way off the correct numbers that I didn't try plugging anything in through
it. (It worked ok afterwards on a regular 120V circuit).

[a] Now... that may or may not mean much for other strange voltages and
cycle settings. reason: I was using the meter on two legs of a three phase
circuit. This is a standard arrangement in many businesses and in a
moderate number of homes. But it's a bit wierd.

In regular 120 VAC you're measuring the potential from one hot leg to
neutral. That gives you a circuit that's cycling 60 times/second.

In what's called "single phase 240V" you've got two hot legs that are
180 degrees apart, so one leg is "pushing" (at 120V) and the other is
"pulling", giving you 240V when you measure across them. And this, too, is
at 60 hz. (I don't have access to one of those, so couldn't test that type
of circuit).

But in three phase you've got three live wires that are 120 degrees apart
in phase. You get standard 120V when you run a hot leg against a neutral.
And... you get 208V (equivalent) when you go hot-hot across two legs of
it. You're kind-of getting two peaks during that 60th/second (and you'd
get three if you measured all three phases/legs together. Most, but
certainly NOT all, appliances rated for 240V will work ok at some
diminshed capacity at the lower figure.

(Note that an EE friend of mine thinks I'm misunderstanding the wave form
on the screen. To me it looks like all those mini peaks are there. But
he's pretty knowledgable so I figured I'd at least mention it).

So I can see how the Kill-A-Watt thought it was seeing 120 hz. However, I
don't see how it got the 173 volt reading. I've been trying to figure out
some sort of fudge factor that makes sense but haven't come up with one,
so suspect it was spurious. (curiously though 173 is similar to 1.73,
which is the square root of 3, and that number has some relevance here...)

Anyway, this does suggest that the KAW _might_ be ok in your situation. Or
it might not...
See above.

3. ### m RansleyGuest

I use it to set my gen Hz

4. ### m RansleyGuest

It is designed for 120 or less but it handles 140 ok

5. ### Gymmie BobGuest

The KaW is only a two terminal device and only sees one waveform no matter
what it's origin. It should always see 60Hz ie: 120 zero crossings per
second.

The 173 Vac is probably the peak measuement capabilty of the internal A/D
circuitry. If you put 208 Vac into the unit the peak of the waveform was
probably digitally clipped off by the internal (guess) 199.9 Vdc measurement
circuit. Now you have a semi squared off sine wave with a peak of 199.9
Volts. When you do your RMS calculation for this waveform the area under the
curve comes out to 173Vac RMS.

The freq reading is confused by this whole thing and reads double for some
reason. This happens because fo the perceieved harmonics sometimes. We have
to know the measurement techniques to really prove it.

Wrong.

Nick

TROLL

9. ### Derek BroughtonGuest

The insights were interesting. Now, for a followup, would it give any
useful information on DC?