Technical Changing location of Bat to trunk/ Ga. of wire?

Guys, I have to respectfully disagree with the notion that 4/0 battery cable must be used. I’ve worked on class five through class eight trucks for 30 years. All of the batteries on class six through class 8 trucks are remote mounted. Now consider this, we are starting 15 or sometimes 16 liter Diesel engines with up to 20 to one compression ratios. Now think about starting this engine in zero degree weather and now we are talking about a 1000 amp draw through the cables. Most of these trucks are equipped with 2/0 cables. Keep in mind that most over the road tractors have 4 group 31 batteries with 950 cold cranking amps. Granted, they often use two 2/0 cables from the positive battery post to the starter, and the truck frame for ground, but I believe that 4/0 cable to start a Small Block Chevrolet with a trunk mounted is very expensive over kill. Have any of you guys priced 4/0 cable lately? 2/0 cable is more than enough for this application.

 

Lots of great replies here about how to go to a lot of trouble and expense, to make it so you won't really want to put stuff in your trunk.



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I Have Been Running a Battery in my Truck for over 42 Year's & Never
had a Problem.
I Run Welding Cable Which if its Good for Welding!
Than its Good enough for My Car.!

Just my 3.5 Cents

Live Learn & Die a Fool

 

I forgot to mention The Gauge of Wire I Use is 200 Copper Strand Welding Cable.!

Just my 3.5 Cents

Live Learn & Die a Fool

 

That right there's a damn good battery! None of them foo-foo battery tenders neither, I take it?

 

While I'm with the guys who use humongous welding cable, I do agree with RmK57. My Miata came with a battery in the trunk, and it had a small cable going there. Also, I ran that car with a lawn tractor battery.

 

All this depends on what you're trying to start. Starters pull a lot of current, even on small motors. I've got some 4 cylinder motorcycles that are only 1100CC, yet the starter draws 90 amps when cranking. A low-compression SBC or SBF may only only draw 175-200. More compression, more draw. More displacement, more draw. Expose the starter to high ambient heat, more draw. Low battery voltage or excessive voltage drop when cranking because of undersized cables or degraded connections, more draw again...

'Average' V8 starter draw is assumed to be about 250 amps. Could be less, but can also be more, a lot more. A big block with some compression and a mild cam (not much overlap to reduce cranking compression) and you can see 350 amps as 'normal'. I had a Jaguar XJS monkey on my back for a while, all of these used a trunk-mount battery as OEM. While Jag wiring overall sucked, they did get the battery cable size right. I've never checked the actual size, but it's bigger than a 2/0 (probably a metric size) and this is to spin a 326 CI V12. When I scrap one of these, I salvage the battery cables...

 

As it came from the factory. 117" long, wrapped in steel spiral sheathing, over the wheelhouse, under the door sill plate, through the kick panel up to the firewall and connected directly to the starter relay.
I'm pretty sure they used a group 29 battery for a little more oomph. Also had special battery vent caps that ran through the trunk floor.

 

I agree with squirrel, I tend to leave them where they came, seems to work well. If you are compelled to move it you can’t put too big of cable for it to work but overkill just results in spending more money.

 

Haha.

I don't want my battery in the trunk but, for me, it's the smartest/easiest spot. There's not a better spot elsewhere that doesn't have some compromise I don't want to make.

 

Early 30s cars, there really aren't many places to put a battery, unfortunately. But later cars, especially a car that has the battery up front and working fine, I'd really really rather leave it up front, away from where people and their stuff want to be.

 

You still got the battery in plan II up front?

 

yup.

Little skinny light weight cables, that I got at walmart cheap....crappy $50 battery...never has any trouble cranking that big bad blown 427.

And I can fit everything I need to drive across the country and go racing for a week, into the trunk. Without a trunk firewall.

 

All washers and hardware need to be copper or brass also if not cover them with dielectric grease , dissimilar metals cause corrosion , corrosion equals a bad connection and weak current flow .

 

My first hot rod had a 350 Chevy with bigger than stock battery cables and the battery wasn't in the trunk. Every time I stopped to get gas, the car wouldn't restart because of low voltage to the starter relay, so I did the suggested idea of putting another starter relay between the battery and the starter relay, it worked. Any guys remember this fix from the 90's? Sure it worked but now you had two starter relays and extra wiring. For the little extra expense and less connections, I'll go the 00 welding cables anytime.

 

I read an interesting (well to me anyway lol) paper on that, a copper washer against a steel frame for example, i causes a type of "fretting" corrosion. Plain old steel washers work better.

Silver is actually the best electrical conductor, but it does corrode, so gold is often used in aviation or aerospace, as it does not.

 

I had a similar problem on my 55....but it wasn't the battery cables causing the problem, it was the purple wire from the ignition switch to the NSS to the solenoid. I measured the voltage on the purple wire when it was acting up, only 7 volts, not enough to fire the solenoid. I added a relay to the circuit, no problems after that. Heavier wire would probably have fixed it. It might have been a high resistance connection somewhere, too....but I didn't troubleshoot further.

 

Mine came attached to my inner fender well. I no longer have inner fender wells.

 

Agreed. The only trunk mounted batteries I had were in stock cars. Of course the lack of money came into play. For the hot cable, I found a piece of ALUMINUM wire in a salvage yard about 30' long. It was about 1/2" in diameter and it worked. Not something I would recommend. Look at trunk mount kits from Summit to get an idea on what wire they use.

 

Ebay for sure. When I was looking for cables for my car, I saw some good quality marine-use stuff. Granted most were short for trim tabs and engine tilts. I ended up having a local speed shop make mine up while I waited for $35.

 

I agree with most of your post with the exception of the star washers! That used to be the thing, but in the fire truck arena ,we have found that the star washers tend to allow corrosion to start. It is now the standard in fire service to not use star washers. I, myself have had failures due to star washers. So I can testify!








Bones

 

This discussion has reminded me about a comment I heard 50 years ago. What I heard was that electricity flows on the surface of the wire so more strands = more surface = more better flow. At the time I was relocating my battery (for potential traction and axle torque upgrade) into the trunk of my weekday driver/weekend drag strip racer and I was buying some by-the-foot cable to do the deed.
I just now did a search and found this on the 'net.......

"Electrical energy travels via compression waves, with the waves traveling through the electrons within the wire. However, electrical energy does not travel through the wire as sound travels through air but instead always travels in the space outside of the wires. This is because electric energy is composed of electric and magnetic fields which are created by the moving electrons, but which exist in the space surrounding the wires."

Maybe there's something to it and multi-stranded, "more flexible" cable may have an actual benefit??
I'm personally dumb as a post about anything electricity and 'little black boxes'. It's all black magic to me. I'm not putting forth an opinion regarding cable but I have often wondered why wiring in any house I've ever seen is always a single strand. (?)

 

To add to the discussion, I`ve got one up front and two in the trunk for over 34 years now.

 

To Understand electricity , you can liken it to the flow of water. But they are not exactly alike…. Just kind of! Lol But then a person has to understand the rules of water flow for it to help them understand electricity!

But the main difference between cars and house current is voltage ( pressure) … 12 volts vs 120 volts = ten times the pressure. That is why houses have smaller wires in them! Also why the starter cables on a six volt car are bigger than a twelve volt car, even though it is only six more volts, it is twice the voltage.








Bones

 

HaHa..... That's easy for you to say.
For slow learners like me, the 'explanations' are the most confusing part of any understanding that may or may not soak in.

 

All electric conductors (wires) are sized by AMPS, not VOLTS. You need to match the wire size for the amperage draw required to operate the device(s) in the circuit, with a 20% margin (industry standard).......this applies to houses and cars.......

 

I started playing with electricity as a kid 60+ years ago! I was fascinated by it! Later in life I maintained a fleet of firetrucks for thirty three years! It was master wiring or fail! If you break it down to basics, the nuts and bolts of wiring/ electricity is fairly simple. I am not a “ Wizard” like “ Crazy Steve” but I think I have a basic understanding and have been successful in chasing shorts and opens for many years. Just remember the KISS rule!






Bones

 

Amps and volts go hand in hand. In order to choose the right size conductors, you will need to know both.




Bones

 

If you are going to do it, I also think 00 is plenty. As mentioned that is what big trucks use. I would get battery cable, not welding cable. I also like a good disconnect right at the battery. I use a bare metal frame ground close to the battery and a 0 dedicated ground cable back to the block also. One thing that I have not seen mentioned is protecting that cable. Needs to be away from exhaust and driveline if running underneath. Cushioned clamps, loom, sharp edge abrasion protection, grommets going through bulkheads, etc. are all important in protecting that hot cable. If you lose insulation and have bare cable to metal contact, bad things will happen. You need a sealed AGM battery or you will have to vent it outside. I would not trunk mount one unless there are no other options.

 

There is such a thing as "skin effect" with cables, but that is a high frequency AC thing. It doesn't apply to 12 volt DC.