Direct short 10 feet round trip circle of 2/0 wire, would that blow ANL 500 amp fuse

Discussion in 'OnBoard Electronics & Controls' started by sdowney717, Nov 7, 2014.

  1. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    I am thinking of fusing starters and the inverter wire.
    I tend to think that it would blow, there will be a few seconds delay and ANL fuses are rated at 140% to blow open.
    I dont want nuisance blows, I just want to open circuit if a genuine hard short occurred.
    I am thinking of fusing the link between the selector switch and positive bus which are within 10 inches of each other. So if that fuse blew, all 12vdc power to the boat is gone. (except bilge pumps)

    (that linking wire is greater than 4/0, whatever the next upsize is, it is like mcm 250, it is very very thick)

    10 feet round trip is about correct for each motor and inverter circuits.
    Boat was built with 2/0 starter circuit.

    reference link
    https://www.bluesea.com/products/5137/ANL_Fuse_-_500_Amp

    I suppose I can buy a 500 amp ANL fuse and short the wire to see if they blow.
     
  2. BertKu
    Joined: May 2009
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    BertKu Senior Member

    Hi Sdowney,

    I am just thinking aloud now. Are there not electronic fuses, which can handle 500 Amp and are faster. I assume it will be in vacuum, like we were using on 500 KW Radio transmitters. Replacing a fuse is always more of a job than pushing a reset button.
    Bert
     
  3. sdowney717
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    sdowney717 Senior Member

    Hi Bertku,

    I think slow blow is good for cranking engine starters.

    I am thinking of making a row of ANL fuses coming off a copper buss bar, sort of like this here
    If I make it, I will design it for 7 spaces for fuses with one 12 volt input from selector switch.

    500 amp port starter
    500 amp starboard starter
    500 amp inverter
    100 amp Lectrasan
    150 amp House (all 12 volt boat use not of the above)
    Extra blank future
    Extra blank future


    Is 7 enough spaces??
    [​IMG]
     
  4. sdowney717
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    sdowney717 Senior Member

    ANN and class T fuses are fast acting, ANL are slow acting.

    In the above picture, it seems there is no fusing of the engine starter, and 4 batteries come into the buss bar and one alternator charger and one 24 vdc charger.

    So wonder if they have 4 on-off battery switches and a single bank charger.

    I have a three bank battery charger.
    My main battery banks are two, each bank has two 12vdc batteries. So I can have up to four 12v batteries in the common battery box.

    The 12v batteries are paralleled together to form 2 independent banks.

    These are all linked into a 1,2, both, off selector switch. The output of which currently goes to a common copper bus bar. I am think of making a fused buss bar instead. I suppose some would have 2 selector switches or even 4 switches.

    My common negative 'buss' is basically joined in a grid on all four 12v batteries in the box, not a separate buss. I could make a separate negative buss with 4 negative wires running from each battery, but that costs money in wire and makes for a longer starter circuit, just not worth the bother.
     
  5. BertKu
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    BertKu Senior Member

    It is alway difficult to precisely fuse a starter, with high start up currents which can vary in cold weather to very hot environment. That is the reason why very few people bother about this. You either over rate it or under rate it.
    Bert
     
  6. sdowney717
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    sdowney717 Senior Member

    ANL is a slow blow fuse that wont blow until 140% of its rated power.
    I suppose it could blow, I think typically about 300 amp surge to get the starter spinning. Cold weather, well your limited also by available battery power.

    I can design it that if it does not work with a fuse, I can bolt the starter wire back next to the input power from a selector switch. I think my bar should allow to have on the unfused side, 2 selector switch inputs and 2 starters, just in case. Although I am thinking I will only use one input to the bar unfused. That Nordhaven photo shows 4 inputs from batteries and one unfused output I think for the starter.
     
  7. AndySGray
    Joined: Jun 2014
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    AndySGray Senior Member

    In the picture, for the 'main eng alt' there looks to be something after the fuse beneath the label panel. Is that a shunt for a charging alternator ?

    Looks like a good setup, what size are the motors?

    You could even put a spare 500 in the two empty slots so you have a spare, with a 'nut driver' screwdriver secured somewhere close.

    The common 8D marine batteries have a 'cold cranking' rating of 650 amps.

    I guess the only real way to tell would be to put a shunt and measure?
     
  8. sdowney717
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    sdowney717 Senior Member

    yes, that tells you the amperage flow from the alternator.

    500 amps times 1.4 = 700 to when the fuse will blow for sure.

    I have a clamp on digital meter that does DC amps. I can check it.
     
  9. gonzo
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    gonzo Senior Member

    How do slow blow fuses compare in price with a breaker?
     
  10. BertKu
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    BertKu Senior Member

    Yes, have a look at http://www04.abb.com/global/seitp/seitp202.nsf/0/6b16aa3f34983211c125761f004fd7f9/$file/vol.5.pdf They go up to 800 Ampere DC.
    Bert
     
  11. sdowney717
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    sdowney717 Senior Member

    I dont know how much the cost difference is. I do prefer breakers, but everywhere I see used on large DC currents are fuses.

    I came up with a wiring scheme I like. It allows me to have a separate starter and house bank. One starter battery for both engines and 2 house batteries.
    Uses 2 selector switches, keeps alternator and charger as they are currently and as OEM did it.

    The 2 maxi fuses could be pulled instead of yanking off battery cables if your worried about alternator line being live and working on the engine. I dont worry about it.

    Starters here are not fused. They could be but I am leaning away from it for now.
    [​IMG]

    If I move the second house positive wire to number 2, then I can unparallel the house banks batteries. Which I think is good idea for testing if one goes down. Can keep the bad battery from draining the good one.
    That means starter bank switch set to number 1.
    And house bank switch set to both to put the 2nd house battery into the charge wire.
     
  12. sdowney717
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    sdowney717 Senior Member

    here is how they did it in 1966.
    Notice they used four 6 volt batteries. No designated house or starter banks.
    Alternator and charger joined and ran to a breaker, then to battery switch terminals 1 and 2.
    (voltage regulator is what they mean by alternator connection)
    And NO fusing of the main 4 gauge wire running to a distribution block.

    [​IMG]

    So at least I am improving things. All the wire is in excellent condition. It is not marine tinned.
    The alt-charger circuit breakers must have burnt out decades ago. Someone who fixed this did not OCPD the wires. Been like that now for at least 20 years I reckon.
    I removed the upper flybridge ammeters and wires and left the lower helm station ammeters. I plan to add digital voltmeters, they are much better to tell you how things are with charging.

    So that cuts out a lot of long wire runs for charging and I get some big wire to use elsewhere.
     
  13. sdowney717
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    sdowney717 Senior Member

    Inside Helm schematic, notice third wire run up is for the charging connection back to the battery
    Green 6 AMP, on terminal strips run back to breakers, then onto the batteries.
    That third terminal connector is the same one spec'd for the charger-converter in the above prior schematic.
    (voltage regulator is what they mean by alternator connection)
    [​IMG]
     
  14. sdowney717
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    sdowney717 Senior Member


  15. Joakim
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    Joakim Senior Member

    Yes, you can blow a 500 A ANL fuse with 2/0 wire (even much longer than 10'). But 500 A is not a safe long term load for a 2/0 wire and you are not able to protect it from heating too much with a fuse that will allow starting in all conditions. A very low ohm short circuit is needed for 700 A current needed to blow a 500 A ANL fuse in less than a minute. 700 A at 12 V is 8.4 kW so some very serious heating can happen without blowing the fuse. Are your batteries able to produce 700 A for a minute?

    Usually there is no fuse, since it really doesn't protect that well.
     
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