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Author Topic:   Question about wiring/fusing for battery disconnect
futurattraction
Gearhead

Posts: 108
From: Iowa City, IA
Registered: Oct 2001

posted 04-26-2003 10:06 AM     Click Here to See the Profile for futurattraction   Click Here to Email futurattraction     Edit/Delete Message   Reply w/Quote
Electrical is not my strength. I've gone back and looked at past threads re battery relocation to the trunk, 1-wire alternators, wire sizing, etc. I don't recall seeing any reference to the need for using some type of fuse between the wiring going from the alternator to the battery. I'm planning on using 8 ga wire (unless told otherwise), as was noted on another thread. Alternator is a 140 amp unit. Do I need to run an in-line fuse and, if so, what size would anyone recommend.
TIA
Scott

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1979 Fairmont Futura, 351C w/Aussie heads, Comp Magnum 280, ProMustang headers, 3" exhaust w/Flowmasters
C6 w/10" converter
9-inch, 31 spl w/3.70s & trac-lok
suspension changes coming.

http://www.avalon.net/~spopham/futurattraction.htm

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Fastymz
Moderator

Posts: 14201
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 04-26-2003 01:06 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
Read this post,

https://mustangsandmore.com/ubb/Forum12/HTML/004227.html

I ran a 8 gauge wire with about 8" of 10 gauge to act as a fusable link.
There are many posts about this topic do a search just type in "BATTERY".

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SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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Dubz
Gearhead

Posts: 1048
From: Manitoba Canada
Registered: Oct 2002

posted 04-26-2003 04:39 PM     Click Here to See the Profile for Dubz   Click Here to Email Dubz     Edit/Delete Message   Reply w/Quote
so this box won't pass tech?

http://store.summitracing.com/partdetail.asp?part=SUM%2DG1200A&view=257#largerimage

got one for a $10 bucks and figured i would use it, guess not

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steve'66
Gearhead

Posts: 7226
From: Sonoma,CA,USA
Registered: Mar 2000

posted 04-26-2003 04:49 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Dubz,

No it won't pass tech. That kit is junk, and I always wondered why Summit sells it they know it won't pass.

SteveW

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Fastymz
Moderator

Posts: 14201
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 04-26-2003 05:07 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
Dubz the only plastic box that I know will pass is the Moroso one.But it costs alot more and it's still not built well.IMO

Steve Money thats what it's all about.I guess some guys want the battery in the trunk but never want to race too.

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SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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futurattraction
Gearhead

Posts: 108
From: Iowa City, IA
Registered: Oct 2001

posted 04-27-2003 09:21 AM     Click Here to See the Profile for futurattraction   Click Here to Email futurattraction     Edit/Delete Message   Reply w/Quote
Thanks for your followup Fastymz!

Scott

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futurattraction
Gearhead

Posts: 108
From: Iowa City, IA
Registered: Oct 2001

posted 04-27-2003 11:59 PM     Click Here to See the Profile for futurattraction   Click Here to Email futurattraction     Edit/Delete Message   Reply w/Quote
Fastymz,
How did you settle on 8" of 10 ga wiring to use as a fusible link? Is/was there a formula (or common electrical knowledge) that provided you with some direction? Thanks.
Scott

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Fastymz
Moderator

Posts: 14201
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 04-28-2003 12:22 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
No Scott,SteveW told me thats what he did.So if it's good enough for him then it's good enough for me too.
I'm sure some one on here knows of a formula that will help explain it better.

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SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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ciscokid
Journeyman

Posts: 77
From: Cleveland, TN
Registered: Jul 2001

posted 04-28-2003 01:03 PM     Click Here to See the Profile for ciscokid     Edit/Delete Message   Reply w/Quote
That 8" stretch of 10 gauge is not going to act as a "fusible link" in any protective measure in that environment. Remember that a fuse works by using resistive heating to cause enough heat to physically melt the conductor so that it opens the circuit. In other words, the fuse (or wire in this case) has to dissipate enough power to generate enough heat to melt. An 8" section of 10 gauge wire has about 680 micro-ohms of resistance. Copper melts at around 1900 degrees F. I'm not sure how much power it takes to cause that high of a temperature rise in an 8" length of wire, but it is a heck of a lot. But, lets be conservative and say that you dissipate 100 watts, about the same as a household light bulb. Ohms law (P=I^2*R for this problem) says that the current needed to dissipate 100 watts across a 680 micro-ohm resistance is 383.5 amps. That is a heck of a lot more than your alternator can supply, and even then I doubt that it would cause the 10 gauge wire to melt. You might burn the insulation off of it, but I suspect that the wire would remain intact.

Fuses are made from short segments of relatively poor conductors (as compared to copper) so that their resistivity does not cause much of a voltage drop under normal conditions, and the power that they do disppipate is concentrated in a very short segment of conductor to maximize the heating effect of the power lost. It is the localized, concentrated heating that causes them to burn open.

As for using a fuse in the alternator to battery connection, it is unnecessary. Stock electrical systems do not fuse protect that part of the circuit. A fusable link is sometimes used between the battery/alternator circuit and the main fuse panel to prevent arcing in case of a break in the high-amperage line that feeds the fuse panel, but the individual fuses that protect each circuit are the primary line of defense for short circuit or overloading conditions.

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Fastymz
Moderator

Posts: 14201
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 04-28-2003 01:31 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
I just put it there is case of an accident,in hope the 10 gauge wire will burn out cut the system.But it sounds like it does not work that way.

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SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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futurattraction
Gearhead

Posts: 108
From: Iowa City, IA
Registered: Oct 2001

posted 04-28-2003 01:57 PM     Click Here to See the Profile for futurattraction   Click Here to Email futurattraction     Edit/Delete Message   Reply w/Quote
Thanks to both of you for the ongoing discussion. I guess you answered my underlying question ciscokid. As I confessed early on, I don't consider myself very well-versed when it comes to electrical systems. I would add the necessary precautions if it were warranted, but it doesn't sound like it's necessary, so I won't do it. Thanks to you, too, Fastymz for your continued interest in this thread!

Scott

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