Re: "Vampire" wattmeter

CJT wrote:
Caesar Valenti wrote:
CJT wrote:

The problem with that is that it gives Volt-Amps rather than Watts,
ignoring power factor.

Sorry, I guess I should have been more specific. This will just provide the current in amps (or 10x amps if using the 10-ohm resistor). To get watts, you must multiply amps by the voltage (typically 115).

No, that gives volt-amps, which only equal watts for resistive loads.
For reactive loads, voltage and current are not precisely in phase.

You are right. I just never think about about the difference since most of my stuff is resistive (switching power supplies excepted, and I almost never measure motors)
think power factor comes into play here, but am not sure.

You are incorrect.
If it does,
would the "kill-a-watt" deal with it?
Yes. In fact, it will display power-factor as an option.

hmmmm.....for the $25-30 cost of this, I may have to get one. Sounds like a bargain....if it is indeed accurate. At one time I read that, for a typical household, trying to compensate for power factor was just not worth it. However, that was before switching power supplies became so common. Does the kill-a-watt tell you if the power factor is due to inductive vs capacitive loading?
.

Relevant Pages

  • Re: Fender amps - bad sounds when the voltage drops (question for the technicians)
    ... and the power was coming through 100ft extension ... occasionally heard the flabby distortion, ... So...the PA equipment did not seem to be affected (Crown and QSC amps, ... voltage, or is there another explanation to consider? ...
    (alt.guitar.amps)
  • Re: Researching my lathe
    ... it is 11.5 amps per the motor plate. ... voltage drop on the 230 or approximately 1/4 the percentage of loss as the ... so the power loss is less apparent. ...
    (rec.crafts.woodturning)
  • Fender amps - bad sounds when the voltage drops (question for the technicians)
    ... During loud sections, my guitar ... and the power was coming through 100ft extension ... So...the PA equipment did not seem to be affected (Crown and QSC amps, ... voltage, or is there another explanation to consider? ...
    (alt.guitar.amps)
  • Re: Transformer drawing 1 amp
    ... 120VAC 50/60 Hz 2.8 Amps ... current of 1.5 Amps at full load on the primary due to the load. ... A true current limiting transformer would have the secondary voltage go to almost zero at something like full rated to twice full rated current. ... During those parts of the cycle, the energy previously stored in the magnetic field are being sent back to the power line. ...
    (sci.electronics.basics)
  • Re: ERNIE, a question I was told to ask you.
    ... of gas" that everyone around here claim remain in the tank; ... You have reasonably stable mains power, but not a lot of it. ... The best machine that I can recommend is the Miller CST280 inverter. ... DC at the maximum output of my welder, 160 amps (well, whatever it ...
    (sci.engr.joining.welding)