low amps

ws9876ws9876 Solar Expert Posts: 385 ✭✭✭
I got a new fuse for a Fluke meter and installed it to check amps on a new but slightly damaged panel installed on the side of the house.
34 volts..not a great location and shaded so that was expected. But the amps showed .062. I thought maybe this was just how Fluke shows
DC amps and it meant 6.2 which was what I expected. Not full exposure and slightly damaged. Then I put out a new undamaged panel
,the same kind, and it showed 4 amps..somewhat shaded...so my meter wasnt off like I thought. Even though it had spider cracks and one bigger bullseye damage it showed 34 volts .... how can this be???

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,644 admin
    Your dmm takes almost zero current when measuring voltage. You can have a million ohms and measure full (open circuit) voltage.

    With current, the quality of the connection is important. If you had 1ohm resistance and 4 amps, then v=I*r or 4 volts drop.

    That is why you have to measure both Voc and Isc.

    For some failures, measuring Vmp and Imp (under real load conditions) is the gold standard.

    Doing Voc and Isc does not catch all failures.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 4,118 ✭✭✭✭✭
    Depending on the amount of shading, I wouldn't expect much current.  It doesn't take a lot of light to get voltage up, but current is more or less directly related to the amount of light hitting the panel.

    For testing, you'd want the panel in full sun, about perpendicular to the sun, and with a load (like batteries in bulk) or short current through the meter.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • ws9876ws9876 Solar Expert Posts: 385 ✭✭✭
    I just went pos to pos and neg to neg...is this no good for testing? I cant believe a panel could be good and read that low on current..
    should I put a battery on the system and measure???
    What is short current thru meter..?

  • EstragonEstragon Registered Users Posts: 4,118 ✭✭✭✭✭
    Short circuit would be +ive to -ive through the meter in full sun.

    Early in the morning, cool but with little light, my panels are near Voc, but produce next to no current.  
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators, Administrators Posts: 29,644 admin
    edited September 23 #6
    If you have two near similar (or identical units) and one produces 4 amps and the other less than 1 in similar sunlight and orientation--The second <1 amp panel is probably bad (when measuring Isc).

    A water analogy.

    You have a water valve and a hose+sprinkler... Full open valve and sprinkler, you have 40 PSI at the valve output, and near 40 PSI at the sprinkler input.

    Now, close the water valve to a just a dribble. If you put a pressure gauge on the valve (no water flow), you read 40 PSI. When you connect the hose and sprinkler, you read zero PSI, and get just a dribble of water.

    Your broken panel is just letting a "dribble" of electrons through the wiring. The DMM is like a pressure gauge with no water flow, and the water flow (current) is like collecting the water from the sprinkler/hose end in a bucket to see how fast the buck fills (gallons per minute, Amps, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ws9876ws9876 Solar Expert Posts: 385 ✭✭✭
    I replaced that solo module with a spare. It looks better anyway. But when I got it in it measured only .05 amps. But on the ground
    at an angle it was at 5 amps. Perfect south both times. Unbelievable how a little angle off can destroy almost all the productivity.
    It is straight vertical on a south wall with about 10% shaded. I only wanted this small system to charge one 12 v battery in the winter.
    The voltage is 36v.
    I have the KID controller. Do you think when I get a battery on it and it runs thru the MPPT that .05 amps will turn into anything useful?
    What would you guess...?
  • EstragonEstragon Registered Users Posts: 4,118 ✭✭✭✭✭
    10% shaded is likely the problem, more so than the angle.  Assuming the shade is roof overhang, will it disappear with lower winter sun angle?  If not, it's unlikely to work well.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • ws9876ws9876 Solar Expert Posts: 385 ✭✭✭
    it will improve in winter but still unbelievable...under the overhang shelters it from icefall ...I will have a ground rack done by next spring.
  • ws9876ws9876 Solar Expert Posts: 385 ✭✭✭
    I had a piece of metal fascia trim on each side of the panel.That was just to cover the ugly cracks on a damaged panel.I put on an undamaged panel and it still showed .06 amps approx. The metal trim was Covering 1 row on each end short sides. I took those pieces off
    and it went from .05 amps to 6.2 amps. Thats what I was looking for.
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