Continuity problem between banks

Discussion in 'Electrical Systems' started by DonB, Aug 8, 2008.

  1. DonB
    Joined: Aug 2008
    Posts: 3
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    Location: Lake Erie

    DonB New Member

    Trying to wrap up 22 ft homebuilt. I've read the books and considered myself closer to smart than ignorant, albeit inexperienced:)

    The two battery banks and connected through an off-on-combine switch.
    The two batteries are directly connected with a neg cable
    The start bank is just that, outboard starter + trim/tilt.
    The house bank connects to a fuse block w/ ground through a circuit break.

    Everything works properly, horn, lights, depth gauge. But there is continuity between the 2 cables connected to the pos batt terminals and the batt switch terminals while the switch is in the off position! Removed the cables and tested the switch. It is OK; no continuity. Removed the neg cable directly connecting the 2 batts and continuity between 2 pos cables is gone.
    What gives? Any advice? Thanks All.

    Don
     
  2. Landlubber
    Joined: Jun 2007
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    Location: Brisbane

    Landlubber Senior Member

    DonB,

    I have to asume certain things are done ok, but let me progress....the cables from the battery +ve posts connect to the battery switch at the rear, these are then diverted via the battery switching arrangement to a single output terminal at the back of the switch, thus allowing either battery 1 or battery 2 or both to be sent to the output terminal at the back of the switch.

    If you take a voltage reading from either of the two input cable terminals, there will be continuity shown as the voltage reading is reading the positive post from the battery , connecting with the negative posts of the two connected batteries, it is irrelevant where the switch position is as you are reading the input to the switch.......
     
  3. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Continuity is measured with a resistance meter. A battery, when in good condition, has a very low internal resistance and a potential of say 13 volts.
    Two batteries with a common minus will show continuity between the positive terminals with near zero potential (13 minus 13 = 0).

    Your electrical system is OK!
     
  4. Landlubber
    Joined: Jun 2007
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    Location: Brisbane

    Landlubber Senior Member

    Correct CDK, maybe that is what he is referring to??????
     

  5. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Attached is a basic setup. Having a dedicated motor battery and seperate battery for other stuff is good practice.

    The switch between the 2 positives is for in case ie the starter battery doesn't turn the motor over, the auxilary battery can be parallelled to assist. This is usually a solenoid switch capable of a 100 + amps. The same thing is used on boats with more than one engine where each engine has it's own starter battery.

    As you can see both batteries are grounded or connected together. If they are not grounded together, you cannot parallel the batteries so easily.

    Also, if the negatives are not on the same potential (gnd), and things can go wrong, you may very well end up blowing instruments from overvoltage or other electrical interferences.

    One thing you may want to pay attention to is cables that lies in water. If they do and there are cracks (they may not be visible) you could get cross-conductance and unwanted current leaks running batteries flat over time.

    Treat wiring like bread :D Dry and clean and you won't have problems ;)
     

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