Measuring Solar Output

Texas Wellman
Texas Wellman Solar Expert Posts: 153 ✭✭
in General Solar Power Topics #1
As many of you know I install solar pumping systems (hence the user name). Since I am not using any kind of battery system or monitoring I have to rely on other factors to know how much power I am generating.

Is there something I could buy that would plug into MC-4 cables that I could branch into my systems so that when I install I would be able to read the Volts/amps/watts output of the array while the system is running? It would be a test-tool and I would simply connect it in-line and then disconnect once I have finished the system. Right now I am using a clamp-on style amp-meter (the pumps are PWM 3 phase and will read on an ac clamp on meter) and have to manually measure volts.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Measuring Solar Output

    Volts is easy: you just need a Voltmeter.
    Watts is calculated as Volts times Amps.
    Amps ... is difficult.

    To get a proper current rating you need a shunt installed inline with an Ammeter attached. The other choice is to use a clamp-on DC Ammeter, which can be reasonably accurate if you follow the instructions and zero it properly from time to time while taking readings.

    I don't know of any measuring tools that just plug in to MC4 connectors. If you want consistent, accurate results you have to hard-wire in the testing tools.
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  • Texas Wellman
    Texas Wellman Solar Expert Posts: 153 ✭✭
    #3
    Re: Measuring Solar Output

    I want to build a box that has digital displays on them. I can supply the correcting wiring interface (MC4). Do you think this would work? Something like this:
    http://www.amazon.com/Digital-Voltage-Panel-Voltmeter-7-5V-20V/dp/B005UWD2J4/ref=pd_sim_sg_5?ie=UTF8&refRID=0S52V8GN7S5TPK8QEBR3
    http://www.amazon.com/Volt-Meter-Digital-Shunt-200V/dp/B005HBBZEM/ref=sr_1_4?s=automotive&ie=UTF8&qid=1403534851&sr=1-4&keywords=dc+amp+meter
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  • Texas Wellman
    Texas Wellman Solar Expert Posts: 153 ✭✭
    #4
    Re: Measuring Solar Output

    I do measure the volts, but I would like to have a "tool" that I can wire in-line between the array and controller that will display volts, amps, wattage etc. It's hard to adjust the array etc. while holding a meter and test leads in one hand.
    Cariboocoot wrote: »
    Volts is easy: you just need a Voltmeter.
    Watts is calculated as Volts times Amps.
    Amps ... is difficult.

    To get a proper current rating you need a shunt installed inline with an Ammeter attached. The other choice is to use a clamp-on DC Ammeter, which can be reasonably accurate if you follow the instructions and zero it properly from time to time while taking readings.

    I don't know of any measuring tools that just plug in to MC4 connectors. If you want consistent, accurate results you have to hard-wire in the testing tools.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: Measuring Solar Output

    There are MC4 connectors that split out an extra connection:

    wind-sun_2270_5066003_1_2.jpg Multibranch MC4 Connectors, Latching

    But at close to $11 each -- Would be hard to justify permanently installing a set just to monitor voltage during debugging. And you would need an MC4 cap to prevent water from getting in the open connector (if not inside a box).

    The easiest would be to open a service panel and get to the voltage there. Perhaps you can wire in a pair of pigtails and cap off with a twist nut for checking during servicing. Otherwise wire up a test port during installation (some sort of DC or non-standard AC plug behind a weather cover). We used to use twist locks or 220 VAC bladed plugs (whatever was cheaper and non-standard for 120 VAC to prevent people plugging in, for strange little connections when needed).

    You cannot use non-contact methods like is done with AC power and measuring the changing AC EM field to measure the presence of AC voltage.

    -Bill

    PS: Never mind on the non-contact AC voltmeter--Don't think that exists--at least as a general purpose DMM.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Texas Wellman
    Texas Wellman Solar Expert Posts: 153 ✭✭
    #6
    Re: Measuring Solar Output

    I'm looking to build a test kit that I would attach when starting up a system and then detaching when I'm through. I would keep the test kit for the next job. I would put the kit between the solar panels and the pump controller box. It would be temporary.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
    #7
    Re: Measuring Solar Output

    Just buy an MC4 cable, cut it in half and separate + and - connections. If you buy a nice clamp-on ammeter you can sample and hold the peak current. Connect the voltmeter and you are good. They also make inexpensive analog current meters that can be used. When you are done commissioning remove your MC4 test cable.
    Texas Wellman wrote: »
    I'm looking to build a test kit that I would attach when starting up a system and then detaching when I'm through. I would keep the test kit for the next job. I would put the kit between the solar panels and the pump controller box. It would be temporary.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • Texas Wellman
    Texas Wellman Solar Expert Posts: 153 ✭✭
    #8
    Re: Measuring Solar Output

    I just purchased a clamp on DC ammeter for this very purpose. Thanks for all the replies.
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  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    #9
    Re: Measuring Solar Output

    One method, could have installing a wattsup meter or it's custom made equivalent
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