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Problem with fuse blowing

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  • Problem with fuse blowing

    I have a tractor and aluminium tinny on my place. Both have 12v lead acid batteries and get only occasional use, In an attempt to get better life out of these batteries I put a 10w solar panel on the roof of the shed above the tractor/ boat and put a cigarettle lighter plug on the panel output and a socket on the boat. No regulator-I have been told a 10w panel can't overcharge such a battery
    It has worked well over the years until recently-I bought a new 10w panel and did everything the same however the new setup blows a 20A fuse on the boat immediately I plug the panel in-almost as if the panel creates a short circuit.I have plugged in a 12v fluoro light in the socket on the boat-all good. I have checked the panel plug for polarity-no problem. The open circuit voltage of the panel seems a little high- at approx 22V.

    I have heard there is a diode built into the panel to prevent the battery discharging at night-could this be the problem? Is it in "the little black box" on the back of the panel.

    All a bit frustrating.

  • #2
    You have a short circuit. Go find it with an Ohmmeter. Start with the Plug by measuring between the center pin and shell where you will find the short. Trace it down.

    Your Open Circuit Voltage (OCV) should be 22 volts on a 12 volt battery panel. .
    Last edited by Sunking; 03-11-2017, 05:18 PM.
    MSEE, PE


    • #3
      So have you personally verified the polarity by testing the voltage with a digital volt meter and not gotten a negative voltage reading? You can test polarity by reversing the probes to see that negative reading. Seems to me not all cigarette lighter plugs are wired the same. Most of them have the positive in the center and negative on the sides. Can you check that all plugs and sockets have their polarity this way. The only other thing I can think of is you may be somehow getting the positive contact on the plug into contact the negative "sleeve" in the socket.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024


      • #4
        Thanks for your answers-I plugged the solar panel in again and noted that the fuse blew exactly at the point where the plug finally made full contact ie when the spring loaded centre (+ve contact) was pushed backwards.
        I carefully examined my soldering on the centre plug and noticed it was off centre- but not by much -I wonder???

        After resoldering the job everything is OK.
        Thanks for refocussing my mind about the short circuit.

        Perhaps blokes over 60 find it hard to believe that they can do a dodgy soldering job!