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Author
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Topic: Question about wiring/fusing for battery disconnect
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futurattraction
Gearhead Posts: 108
From: Iowa City, IA
Registered: Oct 2001
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posted 04-26-2003 10:06 AM
   
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------------------
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
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posted 04-26-2003 01:06 PM
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". ------------------
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
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posted 04-26-2003 04:39 PM
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
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posted 04-26-2003 04:49 PM
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
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posted 04-26-2003 05:07 PM
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.IMOSteve Money thats what it's all about.I guess some guys want the battery in the trunk but never want to race too. ------------------
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
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posted 04-27-2003 09:21 AM
Thanks for your followup Fastymz!
Scott
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futurattraction
Gearhead Posts: 108
From: Iowa City, IA
Registered: Oct 2001
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posted 04-27-2003 11:59 PM
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
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posted 04-28-2003 12:22 PM
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.------------------
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
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posted 04-28-2003 01:03 PM
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
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posted 04-28-2003 01:31 PM
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.------------------
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
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posted 04-28-2003 01:57 PM
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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