Testing my PV's with Multimeter

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nschizzano
nschizzano Registered Users, Users Awaiting Email Confirmation Posts: 24 ✭✭
in General Solar Power Topics #1
2. 12v renogy 100 watt panels. I pop off the black plastic on the back to expose contacts of positive and negative.  I am able collect a voltage reading with multimeter set to DC and V. It is usually around 19v in full sun. How ever when I attempt to gather Amperage data, my reader on displays 2 micro amps on both panels in full sun. Now I know it's more than thay because my MPPT says over 100 watts which would be over 7AMPs. Any one know how to measure Amps on my multimeter and solar panel? What am I doing wrong? I'm just aiming to learn everything in this field.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,467 admin
    #2
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    As I said in the other discussion, you really need to get an AC+DC current clamp DMM to measure current quickly, easily, and safely.

    If you are using a standard Volt/Current meter, you have to "break" the wiring connection and put the meter (set to 10 Amps full scale) in series with the "open cable" connection. You cannot just open the back of the panel and measure current with a leaded meter.

    Your MPPT controller (if all is working well) "calculates" the optimum Vmp-array voltage--Which appears to be around 19 volts... I would have expected closer to 18 or 17 volts--But that number is sort of reasonable. Also, it depends on the MPPT's deciding how much current the battery needs (I.e., a little current, or the full current/power from the array).

    Also, need the MPPT controller's specifications, your panels' specifications, and such... When you run Vmp-array within a few volts of the battery bank voltage, the typical MPPT controller is not very efficient--The MPPT controller needs Vpanel to be, at least 2-4 volts higher than the charging voltage battery to operate "optimally", otherwise you will usually get less than full available wattage from the solar array.

    Makes it easier if you keep all the "related" questions about your specific setup in one discussion. Easier to follow the Q&A.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • faostephen
    faostephen Registered Users Posts: 3 ✭
    #3
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    It seems you are attempting to measure current from the contacts hile you panels are still connected to load (inverter + home loads).

    You can only measure voltage across loaded terminals but current must be measured in series with the load - this means you either connect only the multimeter across the s.panel terminals or you connect it in series with your load.

    The way you are measuring it at the moment, you will only get the amount of current your meter draws from the panel based on its resistance.

    I have attached a rough sketch, assuming you are using a hybrid inverter. Follow same process even if the first landing from PV is solar charge controller.

     
    5KW Growatt Hybrid Inverter, 16 x 350W S.Panels, Off Grid, 10 years
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,054 ✭✭✭✭✭
    #4
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    faostephen said:
     connect it in series with your load.


     


    Be careful using option 2. If your producing more than 10 amps you may blow the fuse in the meter. Most DVM's are limited to 10 amps of current. Another option would-be to get an AC/DC clamp meter which can measure up to 600 amps.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,467 admin
    #5
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    As LH2 says--Always be careful connecting a "wired" Amp meter to any connections... You are exposing "live voltage" (12 VDC - 240 VAC, depending on your source), and while in "volts" (and Ohms, etc.) mode, the meter is pretty "safety" to connect to any rated power source--When switched to "AMPS" mode, the meter becomes a "dead short"--And if you accidentally connect to a Voltage source (12+ VDC battery +/- or the "hot leads" of AC power), you will, at least blow the fuse in the meter, and possibly have other "excitement" too.

    And to sound like a broken record (or would that be a corrupted MP3 file directory these days?), an AC+DC Current Clamp DMM (digital multi-meter) is pretty "fool proof". No "dead short current mode" on leads, no cutting into wiring to connect current leads, etc... Just set to AC or DC amps (if DC, zero meter first before measuring current) and clip onto the wire you want to measure current on. Very safe and versatile.

    A couple of meters to start your searches with:

    https://www.amazon.com/UNI-T-Digital-Handheld-Resistance-Capacitance/dp/B0188WD1NE (inexpensive, 100 Amp max)
    https://www.amazon.com/Auto-Ranging-Resistance-Klein-Tools-CL800/dp/B019CY4FB4 (mid-priced, 400 Amp max)

    I would highly suggest avoiding the "wired" current meters except for smaller/desktop/applications. With $55 for a full function clamp meter, the wired current meter is just not worth the hassles or the risks (late at night, in the rain, trying to debug your AC or DC power system, car won't start, etc).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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