Parallel connection

jmuscharjmuschar Registered Users Posts: 2
I have two identical solar panels, the short circuit current in each is about 5 amps when I check the current individually. However when I wire them in parallel one is measuring 5 amps and the other is measuring 1 amp. It is always the same panel with the low reading. what would cause this?


  • BB.BB. Super Moderators, Administrators Posts: 30,634 admin
    One of the panels probably has an open circuit, shorted bypass diode, or similar...

    Basically, solar panels are a series of (normally) 36 x 0.5 volt cells in series for Vmp~18 volts (if a "12 volt" panel).

    You have "two" easy checks. One is Voc--Voltage open circuit (meter across panel in sun). This checks that your cells are connected in series (Voc~21 volts or so), but if there is a poor internal connection, this test will not find that fault.

    And there is putting the panel on a meter set to measure amps (typically 10 amp scale). And that does show if there is a solid electrical connection--But that is at near Zero Volts. You can have a section of the panel with a failed connection, but a by-pass diode will allow go around that poor connection and the rest of the panel will generate enough your 5 amps in full sun.

    If you have a junction box that you can open and replace a shorted by-pass diode... That is a pretty easy/cheap/reliable fix.

    If you have a sealed J-Box, or there is an open/poor connection in the panel itself--Some folks have cut open the backing and used solder and an iron to fix... And seal the back of the panel up with "liquid electrical tape" or other materials. Not a recommended procedure--And the panel may fail again in the uncertain future.

    If you have a fractured cell, water damage, or other physical fault--Then it is pretty much impossible to fix the bad panel.

    Solar panels can come with a long guarantee (out to 20 years), but getting the company to honor has not always been easy or even possible (many companies have gone out of business).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jmuscharjmuschar Registered Users Posts: 2
    Thanks for your reply. I have done a short circuit amp test and am getting 5 amps. Actuality I have two of four panels doing the same thing.and they are mounted next to each other on my rv roof.  We had a nearby lighting strike that I think may have caused this problem.
    I have been reluctant  to removing the panels to check the diodes but It sounds from your description I may have do do so.
  • BB.BB. Super Moderators, Administrators Posts: 30,634 admin
    At this point--Also search for a good deal on panels (new or used)...

    The prices of panels are so low--That you can usually justify a much larger solar array--And help keep your battery(ies) happy.

    If you wish, we can go into details... What are your daily loads (WH or AH @ xx volts). What is the size and type of battery bank (type of batteries, AH @ XX Volts, etc.). And what is it you need from the system (playing around, emergency backup power, full time off grid operation, etc.).

    If you have lightning in the area--Then surge suppressors may be helpful along with good grounding methods. However, good surge suppressors are not cheap.

    Placing one on the solar array input to your home/shed/charge controller, and another on the AC output of your Inverter (if you have one), is a good start.

    Good luck "J".

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