low power to starter

Discussion in 'Marine Electrical / Electronics' started by wonmore, Oct 8, 2018.

  1. wonmore

    wonmore Member

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    having slow starting issues,changed out agm starting batteries to #31 size and checked voltage to starters and came up low still.At the batteries had the full 14+ volts but at starters drops below 10 1/2.Ran a seperate/additional ground cable from ground buss bar to starter but did not improve.Thinking either existing cables have too much resistance or battery switches are bad.boat seems to have very long cable runs,43 tiara,any input would be appreciated.
     
  2. Old Mud

    Old Mud Captain

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    I would say after all you did Yes, check the + leads. and your batt. switch. That low voltage /Amperage can kill your starter.

    Hey wait, did u say from a buss bar to the starter ? Have to make sure that buss bar will handle the amperage. And the cable from your Buss to your engine is good. And what do you call a "Very long cable" ? Size ?
     
  3. wonmore

    wonmore Member

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    by long I mean from starters all around the stringers across front of engine room to electrical panel,to battery switches down to batteries and then to grounding bar.
     
  4. gary49

    gary49 Member

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    Long cable run means big voltage drop. Diesel starter can draw many hundreds of amps. Our Mainship 34 had cable run lengths on the order of 8' or so. Size was #2. I paralleled new #2 cables with the old ones. Used to have to use 2 8d batteries combined to start the Perkins cold. Now starts easily with either of the 4d's. It made a large difference in cranking speed. If money isn't an issue, you could just upgrade to 4/0 cables.
     
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  5. captjohn

    captjohn Captain

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    First, the cables to both the starter and the ground need to be sized correctly, if their not, you will see a voltage drop during cranking. Next, every connection, on both the positive and negative, must be clean, and tight. Wires can go bad, easy way to troubleshoot them is with a DMM. On the DC voltage setting, put one lead at one end of the wire, and the other lead at the other end. You can only measure voltage across a load/resistance. In theory, their should be no resistance (significant resistance) across the wires. If their is resistance, you will get a voltage reading. If their is no resistance, you will read zero voltage. If you see voltage, that's how much of a drop you are seeing. If you see none, you have no drop when the engine is being cranked. If you see anything significant, a few volts, replace the wire. If you find nothing, repeat the test, one wire at a time, while cranking the engine over. Check all the wires first. If you find a wire that is showing voltage while cranking, and not the others, you should replace it. If their all showing voltage, your wires are under sized, and need to be replaced with heavier wires. Hopefully I explained this well enough to not confuse anyone.
     
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  6. EZ1

    EZ1 Member

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    Very bad tech. Replace with proper gauge wire.

    OP--There's a good chance that the cable lugs are improperly crimped and have high resistance.
     
    EZ1,
  7. wonmore

    wonmore Member

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    thanks for info,will do tests and replace/upsize if needed.
     

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