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200amp battery isolator question

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  • 200amp battery isolator question

    I have an 06 durango with a 200 amp high output alternator. I put a 200amp battery isolator with exciter under my hood to separate my battery in the back from the car battery. I tested the voltage at the alternator and it is putting 14.8 but then I tested it at the batteries and the isolator and I am getting 13.9-14.0. I am losing almost a volt through the isolator. I need to know what the exciter hookup is for and would this not being hooked up be causing me to lose this voltage? It says to hook this to the ignition, so should I just hook it to an ignition wire?

  • #2
    I just installed an isolator and I am getting the exact same voltage drop as you (13.9-14v). The excitation terminal on the isolator is supposed to be hooked up to the sense wire on your alternator, which tells the alternator to output more voltage to compensate. It is okay to leave the excitation terminal un-connected as long as the voltage does not drop too low. Someone correct me if I am wrong, but I dont think all alternators have this sense terminal because I sure couldnt find one on my vehicle. I think 13.9v should be safe. It wont charge your battery up as fast as 14.8v, but it will charge it and keep it topped up.


    • #3
      this is still A problem for me because I am trying to power my audio system and that volt will make a big difference.


      • #4
        i know Diodes burn a small amount of voltage when you use them for limiting / blocking.

        and i think these are the same theory, so a small voltage drop would be expected, 0.6 ish Volts was mentioned here at work


        • #5
          So why exactly is this 1 volt so important? Are you competing in a DB drag? I would say that your previous 14.8v seems a bit high and you might reduce the life of your battery from the overcharging/gasing.

          If you really want to go for no voltage drop, then you either need to connect the excitation terminal to the alternator sense (if there is one), or get a solenoid/Hellroaring isolator which will have no voltage drop.


          • #6
            The exciter hookup I would have thought would be to provide the excitation current that makes the alternator work. Some alternators self-excite, some only need a very small voltage to get them going, and some (older ones) need to be connected to the battery. So if you've installed a battery isolator then the alternator needs to get its start-up juice from somewhere, in your case it probably self-excites. It does sound like it's dropping too much voltage though, usually the schottky diodes they use in simple isolators only drop around 0.2V

            Not hooking the wire up will not affect the voltage drop. Sounds like you just don't need it in your case.

            What makes you think that voltage drop will make a difference to your audio? If it's a hefty system then the DC-DC invertors in it will put out a steady voltage to your output stage regardless of whether you are putting 12 or 15V into it. So long as you can supply the current I wouldn't worry about it.

            Because I'm rude can I ask how much the isolator set you back?


            • #7
              As stated earlier, the excitation lead on the Isolator is supposed to be hooked up to the sensing line of the alternator. It basically includes the same voltage drop that the isolation diodes have, thereby causing the alternator to regulate at a higher voltage. This then higher voltage would end up being correct after the isolation diodes. It is not required, but would be desirable if you can hook it up, as it would keep the batteries at a higher SOC. I'm not sure if there are many alternators made anymore that have this regulator sense line external to themselves. Usually just in RV and Marine applications is where I've seen it (where isolators are almost standard)
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