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

    Yes, I am leaning away from fusing starters as I show in the diagram I made.
    Right now the fuse issue on the inverter, lectrasan and house load wires is going to wait for me to think about the values and design.
    Boat wiring been like the way it is for decades.

    On my positive buss bar, I have a number 4 wire running about 5 feet into a distribution block inside the lower helm station, the wire is unfused. The distributuion block is breakered (has short wires running to a breaker panel).

    There is no conduit on the wire. I will put the wire in a black ENT conduit, I am wondering if a fuse for this number 4 gauge wire is not needed if in conduit??
    Egg Harbor did not fuse the wire.

    This heavy duty ENT conduit is a roll of PMAFLEX black, VOHG 50 meters long, about a one inch width.

    According to the PDF on page 14, it is self extinguishing, so that's good.
    http://www.automation-dfw.com/pdf_elec/pma-02pmafixpmaflex.pdf

    I plan to make use of a lot of this conduit in the boat. I may put the battery wires in it, some bilge pump power supply wires, alternator charge wires, anywhere it might be good.

    [​IMG]

    My roll
    [​IMG]
     
  2. jehardiman
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    jehardiman Senior Member

    Lets look at it another way.

    V= IR and data at http://www.engineersedge.com/copper_wire.htm shows that R = ~ 0.08 ohm/1000 ft, so a 10 dead short in 2/0 would mean that R = 0.0008

    So if V= 12 the I = 12/0.0008 = 15,000 amps, so yes, you will excede the fuse capability.

    Now, is there enough power? P=VI so P = 12*15,000 = 180 kW (which I doubt you have in circuit) so that amperage is not sustainable as Jokaim points out.

    So lets say you have a single battery of 12v with a CCA of 550 amps and a capacity of 200 amp-hrs. So the fast dischare rate is 16,500 amp-sec (550*30) and the power is 6.6 kW (12*550). So it theoritcally could gerneate as much as 15,000 amps for at least 1 second, or more likely 120-150% of the CCA (plate area issue) for 10-20 seconds. Sustained amperage is ~91 (I=sqrt(P/R)) which it could do for ~ 2 hours.
     
  3. sdowney717
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    sdowney717 Senior Member

    yes, I changed my mind on 500 amp fuse. 300 amp fuse should work fine.
    I mean you do want it to blow if there is a short.
    I also decided not to fuse the starters.
    And not to use ANL fuses, they cost too much.

    The Mega fuse is a lot cheaper to do the same thing. Just no visible window, but who needs that luxury. It is easy enough to tell if the fuse is blown.

    The black ENT conduit is very good to work with. I can put my 200 lbs on it and it does not crush at all. It helps organize the wires and gives it some protection. It looks a lot better not having a lot of wires running crazily this way and that. Some of the wire runs I put in the conduit first, then put the conduit into the boat. Technically this is just a wire sheath.

    Conduit is made for THHN that slippery wire. Some wires will never push through conduit. Has to be pulled straight-line, like soft rubber jacketed cords.
     
  4. ncsuengineer1
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    ncsuengineer1 New Member

    sdowney717,
    First post on boatdesign.net...

    Here is a slight spin on your hand drawn diagram. Boat was a single Yanmar with house bank. I used the Blue Sea PN 5511e switches to ease confusion of the operator from seeing 1, 2, both, off for two switches. Turn ON for normal daily use. Aux Starting battery is a "ghost" battery that has charge maintained and no draw until you switch to "combine" on the engine switch. If for whatever reason your engine batteries are toast, you can turn house switch and engine switch to combine to start engine. Each battery has capability of receiving charge from alternator via ACR.
    To link the switches, I used a copper bar with heat shrink in the middle.

    My customer had bought the boat with many underlying problems so this was the first thing to get tackled. I am glad I went with the automatic charging relays because a few days later he was on a trip heading south and the original alternator regulator went out causing a major spike in voltage to the #1 starting battery and fried a few engine gauges. The ACR recognized the spike and prevented damage travelling to #2 starting battery and house battery and all of the electronics, etc. A long discussion with local Yanmar dealer and troubleshooting of problem yielded a new alternator and new battery. It was a long day with travel 3 hours each way but it was a quick fix.


    Let me know your thoughts :)
     

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  5. sdowney717
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    sdowney717 Senior Member

    It looks like the 4 point simple on-off switch is switching in both main and auxiliary starter batteries at the same time?
    (which differs from your written explanation)
    If so you should keep the auxiliary as a backup reserve starter battery separate from the main starter battery.

    Sure are lots of ways to wire these things.
    My boat has two 12SI one wire alternators with internal regulators.
    I suppose external regulated alternators could have more troubles, they might go crazy on the output volts, so the ACR's are good for that possibility.

    I decided it is safer to keep the alternators connected to a battery all the time regardless of the switches hence just putting them on #1.

    My philosophy on battery arrangement for three batteries, why need more than one starter battery? You wont start both engines at the same time. Keep a battery for house with the third in reserve against the other 2 failing-getting drained. I suppose with my wiring, adding a single ACR could keep the third reserve battery charged from the running alternator, even if the selector switch is turned off to it. (Sort of similar to your 'ghost auxillairy starting battery kept in reserve)

    Consider that at the dock, I keep the third battery in circuit, topped up fully charged along with the other 2 using the shore charger.
    Now If I take boat out, I should turn that battery off to keep it in reserve, isolated, just in case. That way I will always have a fully charged battery if I needed it. An ACR would automate that for me, but I have to think about the cost. Maybe a simple relay could do that job, although it would need some circuitry to turn it off and on automatically, like an ACR. That could be as simple as when ignition turns on, the relay turns off and vice-versa.

    I just worked with a minimum cost for making some changes on my boat. I had to buy one more selector switch.

    I have never seen an internally regulated alternator go high on voltage output, not in decades of working with cars and boats. Mostly they just stop working entirely or the bearing wear out.

    On my setup, I dont like paralleling the 2 batteries and a single relay or ACR could help that. On shore power not much issue or even with running alternator. Biggest issue is if their is no active charging going on, one battery failing could drain down the other. But I see looking at other house wired batteries, they wire them up in parallel frequently. I suppose a fully charged battery in good condition could sit uncharged for a month and be ok. But you as a user have to interact with the switches which an automatic relay handles well. Still so far the paralleling has been just fine.
     
  6. ncsuengineer1
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    ncsuengineer1 New Member

    It was a self contained alternator - no external regulator. The dealer said it was a common problem and easier to change out the entire alternator.

    That particular switch leaves the left and right sides independent of each other when "on". See attached for blue sea documentation.

    When the engine switch is "on," it does turn the Aux battery on but it goes no where. The power goes to that "x" on the house switch.
     

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  7. sdowney717
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    sdowney717 Senior Member

  8. sdowney717
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    sdowney717 Senior Member

    Thinking about over volting, I suppose any regulator with an external voltage sensing wire that develops a bad connection - high resistance, will signal to the alternator regulator to raise the voltage. So a 3 wire Delco could also over volt. I just have not seen it.
     
  9. Carioca
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    Carioca Junior Member

    I experienced the effects of over-volting in my car in the late 70´s.....

    After reaching my destination, I was unable to restart the car , so I lifted the bonnet and after some peeking around, spotted the culprit - the battery cable had come off !

    So bolted it together again and the car started, although the alternator light did not go 'off' but kept 'on'...........the overvoltage had fried the voltage regulator, although the sturdy ignition components - coil, points, of old !- took the beating without much ado.

    Fixed it replacing the voltage regulator for a paltry sum, but a happening such as this today, could well run into at least a thousand dollars for the main EFI computer.
     
  10. Carioca
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    Carioca Junior Member

    Nº 6 gauge wire obviously contributes towards minimising the voltage drop, aside from the fact that the principle you refer to is the mainstay of (load-induced) voltage-drop compensation in electrical rotary-generators (more refined schemes feed-in data such as load-current magnitude, etc).

    Should the single-wire alternator power-output terminal be connected to the main bus-bar of the respective battery - NOT the battery terminal - voltage regulation should be just as satisfactory as for the three-wire alternative.
     
  11. sdowney717
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    sdowney717 Senior Member

    A very good reason to keep the alternator always connected to a battery, not designed so that turning a switch can disconnect the running alternator blowing it up.
     
  12. sdowney717
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    sdowney717 Senior Member

    I am glad you mentioned that. I do have the wire on the #1 battery switch post not on the battery terminal. I am recalling it puts about 14.3 volts at that point, it has never been a problem with dimming lights, nothing I have noticed running a one wire alternator. The alternator output wont come on until it spins up fast enough, so hot start at idle, you have to blip the throttle a little to turn on the alternator.

    My battery charger-converter has two sense wires connected to the engine ignition. So when the ignition switch for either engine is turned on, the charger output is turned off. If the cranking voltage drops below 10.5 or so, the charger will come on to give a starting boost, maybe an extra 30 amps. Of course the charger-converter has to be powered on either by shore or gen power to do that.
     
  13. Carioca
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    Carioca Junior Member

    .

    I suggest you browse through the MTA Aftermarket Catalogue, which you may download from the internet. MTA is an Italian supplier to the automotive industry.

    They have a whole array of fuses for specific use in automotive applications, and which may be extended with due discretion to boats too.

    Their PowerVal fuse has been specifically designed for fusing starter motors while a judicious selection within their MegaVal collection should serve as a satisfactory alternative.

    If you show me how to glue a PDF file (on my computer HD) to a post on this forum, I could provide you with graphs of the carachteristics of their fuses !
     
  14. sdowney717
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    sdowney717 Senior Member

    for posting a graph, consider taking a screen shot of the page and then post it as an image attachment or save the screenshots as picture files to google picase, etc, and link it to here using the yellow image icon in the bar.
     

  15. Carioca
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    Carioca Junior Member

    I have converted the PDF files (graphs) to JPG image files.

    Can I bypass the URL requirement to post the image files ?

    In the past, this Forum allowed the user to post images stored on his/her HD.

    I don´t have Picase, Flicker etc
     
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