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  •  » Electrical- mega fuse or circuit breaker?

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    9/21/2015 1:47 PM  #1

    whlnut
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    From: Brunswick, GA
    Registered: 4/02/2013
    Posts: 317

    Electrical- mega fuse or circuit breaker?

    I'm wiring in a 140a 1-wire alternator in my '66. Does it matter if terminated at solenoid or to battery post?
    Local ap stores have mega fuse, but no holder. AZ has a heavy duty 120a circuit breaker. Opinions?

     

    9/21/2015 2:31 PM  #2

    jerseyjoe
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    Registered: 4/01/2013
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    Re: Electrical- mega fuse or circuit breaker?

    You can terminate it at the battery or solenoid.....jj

    "Never put a question mark where God put a period "  Richard Petty
     

    9/21/2015 4:44 PM  #3

    BobE
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    From: White Plains, NY
    Registered: 4/04/2013
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    Re: Electrical- mega fuse or circuit breaker?

    Regarding the choice of 120a fuse or circuit breaker.  A lot of damage (read 'fire') can occur before either will 'open', size the supply wire accordingly.  That being said, I'd use a CB as if it does open, once it cools down and resets, you're good to go again ... of course, you'll need to find out wny it opened and solve that problem.  I suggest added up your loads and size the fuse/CB accordingly, I think you'll find you'll need something smaller to protect the these circuits.

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    9/21/2015 6:41 PM  #4

    BobN
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    Registered: 4/03/2013
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    Re: Electrical- mega fuse or circuit breaker?

    I am using the alternator lead from a 2000 V6 mustang. It is the perfect length to go from the alt to the soleniod and had a fusable link in the wire.

    BobN

     

    9/21/2015 11:09 PM  #5

    whlnut
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    From: Brunswick, GA
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    Posts: 317

    Re: Electrical- mega fuse or circuit breaker?

    The wire from the alternator is 8GA, as specified by Powermaster. How do I choose the correct size fuse or cb?
    Thanks!

       •Thread Starter
     

    9/22/2015 5:00 AM  #6

    wsinsle
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    From: Belle Vernon, PA
    Registered: 4/01/2013
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    Re: Electrical- mega fuse or circuit breaker?

         I would use a mega fuse at about the rated output or a little smaller than the rated output of the alternator. Say a 120 Amp alternator use a fuse between 100 – 120 amp rating. Keep in mind you will probably never go to full output and even if you spike there for a second, fuses usually don’t blow instantly at rated current.
         That being said a mega fuse, by itself doesn’t protect a whole lot. The battery can supply way more current than the alternator can. A fuse between the alt and solenoid would blow if you have an internal short in the alternator, this would be due to the battery supplying high current to the short. This in itself may be a good reason to use one. About the only other thing that would blow the fuse would be a short in the wires between the fuse and battery or some weird battery problem. The issue being, if you use a fuse at or above the rated output of the alternator, it till may not blow.
         Another good place to fuse would be the main power wire leaving the solenoid and feeding power to the cabin. A short beyond this point that is unfused would only melt the wire and could cause fire. A mega fuse at the alternator is not designed to protect this wire.
        
     

    If this forum can't fix it, it isn't broke.
     

    9/22/2015 5:07 AM  #7

    Steve69
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    From: Madison Wisconsin
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    Re: Electrical- mega fuse or circuit breaker?

    I bought my megafuse on Ebay.  They have just about everything you would want.

    Steve69

     

    9/22/2015 8:14 AM  #8

    Rudi
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    From: Stuck in the 50's Welland Ca
    Registered: 4/01/2013
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    Re: Electrical- mega fuse or circuit breaker?

    I used this on my 3-G conversion with a 70 amp fuse right beside the rear mounted battery
     http://www.sherco-auto.com/mm5/merchant.mvc?Store_Code=sherco&Screen=PROD&Product_Code=IBR52

    Good work ain't cheap, Cheap work ain't good!   Simple Man
     

    9/22/2015 9:22 AM  #9

    Steve69
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    From: Madison Wisconsin
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    Re: Electrical- mega fuse or circuit breaker?

    Here's mine on the left on the shock tower. 

     

    9/22/2015 1:22 PM  #10

    whlnut
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    From: Brunswick, GA
    Registered: 4/02/2013
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    Re: Electrical- mega fuse or circuit breaker?

    WS, would it be better to put the fuse between the battery and the solenoid? I am also adding a mini-starter and will move the starter feed cable to the + side of the solenoid. Extra draw will come from AC and electric fan.

       •Thread Starter
     

    9/22/2015 3:30 PM  #11

    Steve69
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    From: Madison Wisconsin
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    Re: Electrical- mega fuse or circuit breaker?

    whlnut wrote:

    WS, would it be better to put the fuse between the battery and the solenoid? I am also adding a mini-starter and will move the starter feed cable to the + side of the solenoid. Extra draw will come from AC and electric fan.

       I put mine between the alternator and the solenoid.  Im running the mini starter too.   I think the worry is the voltage regulator on the alternator going out and the voltage spike coming from the alternator.  Not the fan or ac.

     

     

    9/22/2015 4:42 PM  #12

    wsinsle
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    From: Belle Vernon, PA
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    Re: Electrical- mega fuse or circuit breaker?

    whlnut wrote:

    WS, would it be better to put the fuse between the battery and the solenoid? I am also adding a mini-starter and will move the starter feed cable to the + side of the solenoid. Extra draw will come from AC and electric fan.

     
    No you can't fuse between the battery and solenoid, the starter draws way to many amps to make this feasible. I'm just stating if you are going to take the time to fuse the alternator you might as well fuse the main power wire going to the cabin. Keep in mind these 50 year old cars had no fusing in these areas usually without problems. An original 60 amp alternator can do as much damage on the small wire size as a 120 amp alt can do.

    If this forum can't fix it, it isn't broke.
     

    9/23/2015 1:58 PM  #13

    McStang
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    From: Benicia, CA
    Registered: 4/01/2013
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    Re: Electrical- mega fuse or circuit breaker?

    These are nice fuse blocks - a bit spendy at about $25 on Amazon. I'm using the AMI/MIDI version in the trunk for my alt output with 4g cable and crimp lugs, but they make a MEGA version as well. Not small but iginition protected and beefy (200a capacity), all stainless bus bars & hardware. Cover on the AMI/MIDI stores a spare fuse.

    https://www.bluesea.com/products/category/16/75/Fuse_Blocks/Safety_Fuse_Blocks

    (Pinto!)
     

     

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