Kill A Watt EZ

Discussion in 'General Electronics Chat' started by inwo, Sep 3, 2014.

  1. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Anyone have a model EZ?

    I just noticed that mine won't read below about 10 watts.

    Check of a 7W led bulb read zero.
    Then double check of a 6W incandescent read zero. WTH?

    Borrowed a standard model from the library. Reads fine!
     
  2. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Guess it's normal.

    They don't read low levels.

    The standard one doesn't read a 3 watt bulb.

    Kind of disappointed. :(
     
  3. crutschow

    Expert

    Mar 14, 2008
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    I have a Kill-A-Watt model P4400 and have measured low powered devices down to 1W (although the accuracy is probably not very good at those low levels). Perhaps you have a faulty device.
     
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  4. inwo

    Thread Starter Well-Known Member

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    Strange, the borrowed one is a P4400 and mine is a P4460.

    They wouldn't both be bad.

    I'm guessing "user error" But what could it be???

    Amprobe is fine.
     
  5. inwo

    Thread Starter Well-Known Member

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    I've been testing cheap led bulb to decide whether to use a few in a building that has pf problem already.
    Only a few, so it's not a big deal. Just on principle, I want to be going the right direction. :)

    Even though they are bad. .55 pf it appears to be capacitive.

    The led tubes I've been using are over .90.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    The PF of such a small load is of no consequence compared to the power used in a building. A capacitive power factor is actually an advantage since it cancels some of the typical inductive (lagging) PF that is common in the mains supply.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    Does it register any VA for small loads?
     
  8. inwo

    Thread Starter Well-Known Member

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    No, does not show amps or VA.
     
  9. tindel

    Active Member

    Sep 16, 2012
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    Wait - you can borrow a kill-a-watt from the library?
     
  10. inwo

    Thread Starter Well-Known Member

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    My wife, the librarian, said Excel Energy donated two of them. :)

    edit:
    She also has 35 pair snow shoes to lend.....................................
     
  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Ha, I just learned that libraries around my area 'lends' garden seeds (tomatoes, cucumbers, ...), small power tools and camping gear.

    The seeds require the borrower to pay back with seeds from the crop you plant.
     
  12. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    AFIK, the Killawatt is pic-based. There is only so much you can do with a 10bitADC
     
  13. creakndale

    Active Member

    Mar 13, 2009
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    I have the Kill-A-Watt EZ Model P4460 that I initially purchased to gather data on Phantom Loads (I guess the new term is Vampire Power). Although I do use the EZ often, it is not a good tool for measuring small power consumption which has been a disappointment. Yesterday, I ran some tests to determine it's actual low range usefulness. I used a 7.5W incandescent bulb and a Variac feeding the Kill-A-Watt EZ. I don't have a variable load so I used the Variac to lower the voltage, thus the current, power and VA to obtain the lowest non-zero readings my EZ is capable of displaying.

    Lowest readings I could get: 51 Volt, 0.06 AMP, 04 Watt, 05 VA.
    As I turn down the Variac below 51 Volts, the Kill-A-Watt EZ's display dims and is unusable.

    creakndale
     
  14. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    They may be capacitive, but you can't tell that from a reading on the Kill-a-watt. The PF measurement on the Kill-a-watt doesn't distinguish between capacitive and inductive power factor.
     
  15. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    It's possible to make a hardware modification to the Kill-a-watt P4400 which will increase its sensitivity and make the measurement of "vampire" loads more accurate. My Kill-a-watt P4400 has an internal shunt consisting of a short piece of manganin wire. I bought another P4400 Kill-a-watt at Fry's, removed the shunt and measured it with a 4 wire ohmmeter. It's a 2 milliohm shunt. I then replaced that shunt with a .2 ohm, 2 watt 5% wirewound resistor, choosing the most accurate one from a bunch of them. Now the modified Kill-a-watt has 100 times the sensitivity. I was able to measure the no load draw of a modern wall wart at .077 watts. The maximum power measurable is now 18 watts. I compared the reading with my high sensitivity, low power factor Yokogawa wattmeter, and it was very close.

    Some "Kill-a-watt" type meters, or other models of the Kill-a-watt brand, may not have a 2 milliohm shunt, but the P4400 I modified did have a 2 milliohm shunt.

    For the final accuracy check, I just set the modified Kill-a-watt to measure current with a small purely resistive load, and compared that to the simultaneous current reading measured with a DVM. The modified Kill-a-watt reads 2% low. A person could trim the .2 ohm shunt, or just add 2% to the reading. To trim, I would start with a .2 ohm resistor that measured high with full length leads, as measured with a 4 terminal ohmmeter, solder in the resistor with near full length leads, and then shorten them as a method of trimming. Or, solder in a .22 ohm resistor and solder in an additional resistor(s) in parallel to trim.

    Edit: A good idea to protect the modified Kill-a-watt from start up surges would be to solder a couple of 1N5400 series rectifier diodes, back to back, across the .2 ohm shunt. For normal currents (less than .15 amps) the diodes will have no effect, but will protect against loads that draw a start up surge.
     
    Last edited: Sep 6, 2014
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  16. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Amprobe shows it to be capacitive, as I would expect. Cheapo driver seems to be a bridge, cap, zener, resistor combination across the line.
     
  17. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Thanks, I may look into that. Just what I was hoping to hear.
     
  18. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    What model Amprobe is that?
     
  19. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    ACD-30P

    Does not do thd. :(
     
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