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Logic 1 unit voltage.

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    Logic 1 unit voltage.

    Hello all. I was wondering if anyone knows what the "off load" voltage of the logic unit is when it is connected to the mains ?
    Under mains connection via the "Hook up":
    When the unit is connected to the panel etc the voltage across the terminals is 10.6 v. Surely this isn't enough to charge the leisure battery?
    When the terminals are disconnected the voltage from the unit only rises to 82V, again that cannot be a correct "off load" voltage output can it?
    I know that the wiring has been interfered with as the leisure batery is running in parallel with the main battery. The leisure battery only powers a cig lighter socket and all other functions, internal lights, pump are at the moment running off the main battery no matter which way the panel switches are put.
    The van is 1991 Hytop.

    It is difficult from your desciption to diagnose your problem. "Long Range" diagnosis is always chancy, but if some things work off one battery without the other they are not truly in parallel.
    Your leisure battery should only be (automatically) connected in parallel when the engine is running and charging BOTH batteries. It sounds as if some wiring which should be connected to the leisure battery has been transferred to the vehicle battery terminals.

    If your leisure battery is well below the recommended discharge voltage an intelligent battery charger may only show 10.6 volts when connected, but the voltage should rise as battery voltage increases. It should always be slightly more than the battery voltage when charging to force current through the battery.
    The open circuit voltage is something else and the charger may need to be connected to assess battery voltage. 82V though is a tremendous voltage and would destroy your battery if it is maintained during charging. Maximum vehicle battery charge voltage is usually 14.7V (from the alternator, measured at the connected battery with the headlights on), but it is NOT checked open circuit.

    Make sure if you are using a multi meter that it is set to measure DC Voltage. I have never tried an AC setting with DC, but it is bound to give strange results.
    Last edited by Twolitre; 26-06-2011, 20:01.
    Keeping people waiting is stealing a part of their lives.


      Thankyou for your reply.
      All the voltages are being read in DC on a reasonably expensive digital multimeter of which I am an experienced user. The batteries are wired in parallel by a 3mm lead +ve to +ve and -ve to -ve and not series. The onboard pump and lights are driven off the car battery which is proven by removing the +ve terminal (as -ve is common) on the leisure battery and operating the pump etc.
      My concern is the +80 V that is coming off the terminals of the charging unit when it isn't under load. It seems a (dangerously?)high voltage from a charger even when it is off load. dropping down to 10.6V DC when under load still seems insufficient to charge the leisure battery. (Which is reading 12.4V without load) I have checked, there is no leakage and the casing is safe.

      I suspect that unless it can definately be confirmed that the 80+V is acceptable and that indicates that the charging unit is working correctly, I will have to replace it with a 30amp switching relay which will monitor both batteries and switch on board facilities to leisure when the engine is not running. Mains charging can be taken care of with an onboard charger which can be switched on when needed.
      Does anyone know the tech spec of the logic 1 unit please?
      Or has anyone ever measured the off load output of their unit?


        Hi can't help a lot with this, but I know a man who can!

        Post your question in the Ask Ant question, he'll know about those units if anyone does!

        Your leisure battery 'should' be powering 12v lights and water pump at the least, I would have thought.


          Hi Orkney viking.
          I'm afraid it sounds like your Logic 1 has died. I've had one drop its voltage regulator before and had similar readings to yours. One minute it was charging at less than the battery voltage the next it was boiling the battery!
          My advice would be to remove it and replace it with a stanard ( Halfords type About £10) battery charger with an inbuilt over charge function. Don't buy another Zig unit they're about £150 and do no more than a cheap charger as far as charging the battery is concerned. The switching on the panel can be left, and will switch between batteries as normal, just remove the charging wires and substitute a charger. What you will lose is the transformer function (240v to 12v) but you've probably not had that while its been dying anyway.


            Thankyou for the reply and the confirmation.
            It sounds much as I suspected. I didn't like 80+V DC coming off from what should be around 14.5V. The solution you gave is that which I thought would be the only answer. I Knew someone would be able to give a definitive answer. Happy motor-homing.


              I do think you would be well advised to refit a split-charge relay between the batteries - oh so easy to flatten both the way they are wired now!!



                Thankyou for your replies.
                I have purchased a split charge relay and new battery charger plus wire and fuse box etc. That should sort it out. I shall consign the Logic unit to the recycling point. I guess that I can still use the logic panel as the feeds and outputs will still be in place. I shall let you know how I progress. I have re-wired the mains input which is now completely separated from the logic unit. I am looking to add a further earthing point and welcome any suggestions as to where to put it. (Please be kind !!!) The RCB is still in place and mains is wired through it.


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