Can I Measure Grid-tie Inverter Output With a Kill-A-Watt Meter?

Tyler
Tyler Registered Users Posts: 3 ✭
edited December 2019 in General Solar Power Topics #1
I have successfully used a Kill-a-watt meter to measure the output of my grid-tie inverter by reversing the plug input and output, but that was while the sun was shining. However I'm not sure what will happen when the sun goes down. Will the meter be OK with the mains voltage on the output side and no power coming from the inverter? Secondly, can I just plug the meter in normally, and measure a negative power usage?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    I have never tried it... But go ahead, it should not damage the meter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #3
    Are you trying to get a cumulative reading or just a 1way reading?  As far as I, know the Kill-A-Watt meters are just 120 volt.

    You can get a regular meter pretty cheap, might even be given an old dial type if you ask nice at the electric company, a lot of them around, as power companies have switched out most of the dial type for digital.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    In the US, many (some/most/?) of the "plug and play" GT Inverters (typically less than 1,000 Watts) seem to be 120 VAC...

    There is a good chance the original poster is from the South Africa region--So, he would probably be using 230 VAC @ 50 Hz anyway.

    And, you do not want to exceed the current rating of the Kill-a-Watt (or similar) meter.

    If Tyler comes back, there are a whole bunch of questions and answers we can get into--If he desires.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Tyler
    Tyler Registered Users Posts: 3 ✭
    #5
    Yes, I'm in South Africa so I'm on 220 v. My "killawatt" meter is actually a mail-order no-name. And it's a 600w gt micro-inverter, so no power issues. And I want to measure cumulative, so an old meter is not ideal. There's no smart meters here, no tax credits for going green - just a very corrupt Gov't with an overpriced "state-captured" utility company. So I'm just trying to shave 10% off my electricity bill, and do it as cheaply as possible. But I need to know if it's actually working, and so I need to measure the output - preferably  cumulatively. I've seen a couple of videos where killawatt meters were used - in both cases they appeared to be plugged in normally, so they seem to be reading a negative current - clearly not what such meters were designed for. Me, I flipped it around, but then at night I'm concerned the meter might blow. But also concerned the same might happen in the day if I plug it in the "right" way into the mains. Bill, you say it won't damage the meter, but which way do you mean - when plugged into the mains or when plugged into the inverter?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Technically, AC voltage and AC Current is always going back and forth (+voltage/-voltage, +current/-current).

    Think of pedaling a bicycle, it is when in the cycle (like voltage, the position of the pedals) that you apply force (like current)... Apply force in 1/2 the rotation, you go faster. Apply force in the other 1/2 of the rotation, you go backwards.

    How the power meter will choose to display the two different voltage/current timings, I do not know. Will it simply say 100 Watts? Or will power going the normal direction of the meter display 100 Watts, and backwards power flow display 100 Watts or zero Watts, or something entirely random... Don't know. Depends on how it is programmed (or if the programmer even took the power flow direction into account).

    A simple test... Take a known load and apply it normal direction (meter input plug into AC outlet, meter output receptacle to AC load). And see what happens when you plug the meter in "reversed".

    There is a danger involved... In the US, for example, when you wire an extension cord with two Male Plugs to "jumper" power... We call that a Suicide plug or cord. If the plug is pulled from the receptacle, it will be "hot" and could electrocute somebody with the exposed blades.

    I think I am understanding your questions and answering them... If I am missing something, please ask again.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Tyler
    Tyler Registered Users Posts: 3 ✭
    #7
    I plugged the meter in the other way, and it seems to work fine. So for those of you using a small microinverter system and on a budget, it looks like you can save on the cost of a dtu monitor, and just use a relatively cheap electronic power meter. Bear in mind, I don't know if it will work with any power meter, so it's a gamble.
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