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Thread: Couple of electrical questions if you please?

  1. #1
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    Couple of electrical questions if you please?

    I'm committing to the glow plug switch to the solenoid to glow plugs project and I need to know.

    In the diagram provided by marinehowto.com I have:

    A) A 10 AWG min fuse from the starter post to the solenoid. Fuses are good I like them, AWG = 10 amps minimum? yes? can a larger fuse be used in this position? How large, Max amperage?
    Three questions for one.

    B) How about a large amperage fuse, say 150 amps between the "I" side of the solenoid switch to the Glow Plugs ? Would a fuse that large be overkill?

    P.S. One last question please I don't see any power coming from the alternator? or Batts? so all the power travelling through the switch is coming from the Starter Post during crank?
    A two fer.

    Amazon is offering a Cole Hersee (24059 BP) including two of these 150 amp fuses and I'm thinking this can work. Open to any comments or suggestions,

    Thanks,

    Dan
    1988 E-32-200 M-25 engine

  2. #2
    1984 Ericson 30+, Nanaimo, BC
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    Hi,
    I'm not an electrician, but I would determine how many amps of current will be flowing through that circuit. Then I would use a slightly larger fuse for some "wiggle room", as an undersized fuse will burn out frequently. But I wouldn't use too large a fuse, cause then it won't protect the circuit by burning out when it should. To me a 150 fuse sounds way too large. I would be inclined to use a 30 amp fuse, but best to calculate how much current will run in that circuit.
    Just my thoughts... I'll be interested in what others suggest.
    Frank
    Last edited by Frank Langer; 11-08-2019 at 05:35 PM.

  3. 11-08-2019, 05:35 PM

  4. 11-08-2019, 05:41 PM

  5. #3
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    Quote Originally Posted by Frank Langer View Post
    Snip... best to calculate how much current will run in that circuit.
    Frank is onto something here and there is a tool that will help with your inquiry.

    http://circuitwizard.bluesea.com/#

    Highlighting a field popups a window of explanation/definition. Insert the data as best you can and you'll get a recommendation for wire and over circuit protection (read fuse or breaker).

    Over circuit protection is not for the device, but to protect the wire and insulation from turning into a toxic lightbulb and burning down the house. Use of the calculator is highly recommended.

    Max
    September Sun
    ERY35240D686

  6. #4
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    As Frank and Max wrote, the protection is sized for the wire and the wire is sized to the device on the end, in this case the glow plugs. So the first step is to know how many amps they pull and that should be in the owners manual.
    https://www.westerbeke.com/technical...hnical_man.pdf

    Page 19 has the plugs so multiply 7A times three plugs and get 21 amps. Uprate that by a third for corrosion resistance and other real life factors and you are at about 32 amps.
    Enter that 32A in the Blue Sea calculator and your 10 ga cable should be fine for an estimated 10 feet of total circuit length. (battery to solenoid PLUS solenoid to plugs; the plugs themselves are the ground)

    Now in the calculator add your circuit protection data and it will give you a chart which shows a variety of choices for the optimal protection device. For example, this suggested 50A fuse will give you more than double the 21A needed by the plugs yet is going to trip at half what the cable can carry:
    https://www.bluesea.com/products/517...nal_Fuse_-_50A

    Note that your proposed 150A fuse is not going to protect the cable. The cable will burn before the fuse blows. (Wouldn't you rather have a breaker?) For example if the cable rubs on the engine and a dead short develops. (ALWAYS assume a dead short like this will happen as it is the most conservative case.) Just to show why over-rating the protection is such a bad idea, below is the info for a 150A breaker and it shows the device will take 5,000 amps for 1 full second. (Really it'll just go to whatever the battery could provide.) At that point the cable can become an ignitor for any nearby fumes or wood it may have been touching and it would have destroyed/shorted/overloaded any wires routed with it.
    https://www.bluesea.com/products/704...nel_Mount_150A

    If doing this in the future and if you want a good reference to keep on the boat for when out of touch with the internet, print a copy of a wire chart like this:
    https://www.marinco.com/~/media/Webs...ltage-drop.png

    If sizing for a new device on the end of a wire, the rule of thumb is 3 times the amperage for the load on the wire and a breaker or fuse sized to that. For your case you can see that tripling the load of the 3 glow plugs (7A each) comes to 96A for the 10 ft cable and 100A just so happens to be what the chart and calculator both arrive at.
    Last edited by Tin Kicker; 11-09-2019 at 09:44 AM.

  7. #5
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    Thanks Frank, Max and Tin this was excellent information indeed!

    Frank yes you just saved me the cost of these fuses that would have been too much for the load indicated. Also thank you Max for the link to the "tool" and to Tin Knocker for doing the calcs. I did check your numbers and they agree.

    I feel far better armed with this information,

    Thanks to all of you.

    Dan
    1988 E-32-200 M-25 engine

  8. #6
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    Quote Originally Posted by Soupy sails View Post
    Frank yes you just saved me the cost of these fuses that would have been too much for the load indicated. Also thank you Max for the link to the "tool" and to Tin Knocker for doing the calcs. I did check your numbers and they agree.

    I feel far better armed with this information,

    Thanks to all of you.

    Dan
    np.
    LOL - Hadn't about a Tin Knocker (metal boob?). A Tin Kicker is an accident investigator.
    https://howitbroke.com
    cheers

  9. #7
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    A solionid is not really the right application here. a relay is more appropiate. The relay on Terra Nova has been working well for five years now. The total run from the battery to glow plug is under 6 feet. The voltage increase at the plugs compared to before (9.7 volts at the plugs to 11.9 volts at the plugs). The Universal sure likes to start now compared to before.
    Bob Morrison
    1987 E-34 Hull #15
    "Terra Nova"

  10. #8
    Principal Partner Tom Metzger's Avatar
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    Lots of good advice here and lots not so good.

    Fusing to protect the wire is a great concept, and that is a requirement, but it is not the be all/end all. It's great that the wire doesn't cause a fire, but do you want the device at the end of the circuit to cause a fire?

    Fusing for the wire size is the way to go if you are fusing from a source and will be splitting into branch circuits that will be protected with fuses or breakers. Think battery to DC panel. Those branch circuits should be sized for the load unless the load is also fused.

    With the glow plugs, 3 of them at 7 amps you want to use #10 AWG wire and I would fuse the wire near the starter solenoid at 30 amps, 21 amps + 25% next highest size. The 25% is a factor of safety to avoid false blown fuses or bkr trips, not because of corrosion which would reduce the current. A fuse or breaker will carry approximately 125% of rating forever, 37.5 amps in this case.

    If sizing for a new device on the end of a wire, the rule of thumb is 3 times the amperage for the load on the wire and a breaker or fuse sized to that. For your case you can see that tripling the load of the 3 glow plugs (7A each) comes to 96A for the 10 ft cable and 100A just so happens to be what the chart and calculator both arrive at.
    I have a problem with the methodology. 100 amps through #10 wire equals fire. Three times the load current makes no sense as it would increase the required wire size. According to the charts on the Blue Seas site my solution works. 50 amps would be the largest fuse allowed in an engine compartment for #10 wire.

    http://assets.bluesea.com/files/resources/reference/20010.pdf


    P.S. One last question please I don't see any power coming from the alternator? or Batts? so all the power traveling through the switch is coming from the Starter Post during crank?
    A two fer.
    The current comes from the battery, and the charger if you are plugged in. Those are the only sources there are until the engine starts.
    Tom Metzger
    E-34 Xanthus

  11. #9
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    Hey Tom, thanks. I really sat down and read this one. This proposed system needs to go back to the drawing boards. You cannot pull the power off the starter solenoid for the glow plugs. They must be activated prior to the use of the starter. A solenoid is the wrong equipment to use to energize the system and a high amperage fuse is a fire waiting to happen. This is a high amperage circuit that can easily burn your boat to the waterline. Don't commit to this project until you are sure exactly what you are doing.
    Bob Morrison
    1987 E-34 Hull #15
    "Terra Nova"

  12. #10
    Principal Partner Tom Metzger's Avatar
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    This proposed system needs to go back to the drawing boards. You cannot pull the power off the starter solenoid for the glow plugs. They must be activated prior to the use of the starter. A solenoid is the wrong equipment to use to energize the system and a high amperage fuse is a fire waiting to happen. This is a high amperage circuit that can easily burn your boat to the waterline. Don't commit to this project until you are sure exactly what you are doing.
    OK, it's after cocktail time in the east, but... The gazinta post of the starter solenoid is always energized. A solenoid is a simple relay intended for high current low voltage applications. Could any 30 amp relay or contactor do the job? Yes, of course, but an automotive starter solenoid is cheap, easy to mount, and can certainly do the job.

    BTW, all the people who rewired their engine panel per my Universal Engine Wiring Upgrade, or whatever I called it, powered their engines off of the starter solenoid. It works.
    Last edited by Tom Metzger; 11-09-2019 at 06:52 PM.
    Tom Metzger
    E-34 Xanthus

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    Did I miss it or has wire gauge / length / load / voltage drop been completely ignored?

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    Quote Originally Posted by Parrothead View Post
    Did I miss it or has wire gauge / length / load / voltage drop been completely ignored?
    The links showed 10ga was fine by the Blue Seas calculator and the wire chart without breaking that detail out in this thread.

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    I did not see any mention of circuit length anywhere in the thread and without it voltage drop cannot be accurately determined.

  16. #14
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    Quote Originally Posted by Tom Metzger View Post
    With the glow plugs, 3 of them at 7 amps you want to use #10 AWG wire and I would fuse the wire near the starter solenoid at 30 amps, 21 amps + 25% next highest size. The 25% is a factor of safety to avoid false blown fuses or bkr trips, not because of corrosion which would reduce the current. A fuse or breaker will carry approximately 125% of rating forever, 37.5 amps in this case.
    We're coming at the 25% and 33% (third) from different standpoints of a design engineer and designing a repair. The 25% is more efficient and normal for a production installation while using thirds is normal in the field. For either, the 10 ga wire works.

    I think my intent about the cable size was lost in how I worded the sentence you objected to and I certainly was not implying that 100A should be run through 10ga. My point was simply about uprating the wire to more than the fuse or breaker was rated for.

    Below is the Blue Seas chart showing the 50A is called to be nominal. Using the lower current for 25%, the 30A c/b would acceptably be on the low side of what they show as nominal.


  17. #15
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    Quote Originally Posted by Parrothead View Post
    Did I miss it or has wire gauge / length / load / voltage drop been completely ignored?
    21 amp load plus a margin of safety makes #12 AWG 105*C wire the minimum acceptable size for use in the engine compartment with a 30 amp Maxi fuse. This per the Blue Seas chart I referenced and their on-line calculator. I don't know why they don't use a 30 amp ATC fuse in the engine compartment for #12 wire; they do for #14. http://circuitwizard.bluesea.com/

    FWIW, Maine Sail recommends #10. Either would work for short runs. I would probably use #10 because I have it.
    Tom Metzger
    E-34 Xanthus

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