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what gauge battery wire

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battery
13K views 46 replies 21 participants last post by  EOD Guy 
#1 ·
have have 69 gmc with a 350 and a red top optima
i was wondering what gauge wire i should use for the battery
i didnt know if the better battery or any would need different gauge
the battery will be under the hood
 
#3 ·
return the red top if you can..
get a normal lead/acid battery..
we've had to warranty every red/yellow top battery we've sold..
if you run the battery down you have to trickle charge it.. letting the alt recharge it. will kill it..
they are great for racing, no chance of acid leaking.. but normal use. they are crap.. if you ever run them down.. slow charge on a trickle charger or battery tender like charger..
 
#7 ·
I've had trouble with every Optima I've owned over the last 15 years (4). I'll never buy them or recommend them to anyone for any purpose.

As far as cables go, If I am upgrading or installing any cables going forward in any vehicle I truely care about I will be using welding cable. Preferably 1-0. It conducts better, it's much more flexible and far more resiliant to damage and heat. Whenever I terminate new cables I solder them with a torch and it's amazing how well the jacket on the cable holds up to direct flame without melting.

It's a bit more money, but well spent IMO.
 
#11 ·
I've been using this technique on the general wiring on my project. Very time consuming, but also very reassuring. How do you crimp the lugs on heavy cables? Is there a special tool you'd recommend? Do you recommend just using a vice? Inquiring minds want to know. Thanks in advance.

Pat
 
#12 ·
There is a tool if you are crimping a lot of them. Here: Heavy Duty Hammer Crimper

You can also use a 1/4" round steel rod and a vise - better than just smashing them with the vice - use the steel rod to focus the crimp. For large cast lugs, I usually drill a small hole in the end and use that to solder the connection.

When I can, I use adhesive-lined shrink tube - makes the connection waterproof. I buy the clear shrink tube - when it's sealed up, you can clearly see the connection and the wire color. (like the connections on the right in the picture).
 

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#13 ·
Use welding cables. They work the best(by far). Go down to your local welding supply store and ask for welding leads. Then just buy the end terminals and the bolts. I like the quick disconnect switches like the ones below.(you can get these through jegs or any aftermarket parts place)

 
#16 ·
The fine wire cable, like welding cable is so much more flexible and easier to work with, but you still need the gauge. The longer the cable, the greater the voltage drop. A short 4 gauge wire will work, but put that battery in the trunk and run 15 feet of that 4 gauge and you will have a bad voltage drop - you make up for that by using the larger gauge. I used 1/0. If that was heavy wire like most battery cable, it would be hard to work with because it would be so stiff.
 
#18 ·
Fine wire or coarse, for a long battery cable you still need a large gauge. Fine wire in 2 gauge will not carry more load that 1/0 coarse. Your own qualifier "...in the same overall gauge" may be true (I have seen it debated more than once), but in this instance you have to have a large gauge to minimize the voltage drop.

I have read that when dealing with high voltages, that the current travels over the surface of the conductor, meaning that the fine wire havine more surface area, carries more current. However, with low voltages such as a 12v auto electrical system, the current is carried through the conductor. There is nearly an identical amout of copper in both cables.
 
#21 ·
Welding cable is for welding, that's why it's called welding cable. It's made of fine strand wire so it will give the flexibility needed for welding. Look at the ratings for insulation on a wire distributors web site, (Try Waytek.com). Welding cable insulation is normally only rated for water resistance. Automotive, aircraft, and marine wire is rated for oil, grease, gas, and acid resistance. The gauge of the wire is what matters. The number of strands does not matter to D.C. voltage, D.C. current flows through a conductor and "skin effect" where the current flows on the outside of a conductor only happens in the upper radio and microwave frequencies.
 
#25 ·
professional electrician here. unless you are running 20ft of wire or more 4ga wire will suffice. you can buy 4ga THHN from home depot or lowe's but its expensive and doesn't bend as easily as welding cable but the insulation is rated for outdoor use and burial, very u/v resistant. good wire overall. the number of strands and it's relationship to current carrying capacity is null. 4gauge wire(bare) is rated for 100 amps whether it's THHN, SOOW, or type W. If you can find EPDM that would be the best for automotive use if you are that particular about it. the types of wire insulation will also determine the ampacity of the wire. 4ga SOOW is not rated for 100 amps, its rated at 65. the insulation has to be able to safely transfer the heat created by the load. SOOW is low cost compared to type W(100 amp rating). insulation specs also address environmental issues that can de-rate the wire. however, for the application in question, 4ga ANYTHING will work. unless its bare copper(duh). my personal preference in my camaro is 2ga EPDM because i have access to it for free. it's fine strand, dissipates heat well, takes the harsh underhood environment, and is more than big enough. the specific resistance of copper doesnt change with strand consistency (fine/coarse). the disadvantage of fine strand is when it starts to corrode it ampacity goes to hell in a handbasket quickly because of the air gaps between the strands. but if you seal the wire ends with a good heat shrink with adheisive like 3M you should never have a problem. fine strand wire handles heat dissipation better than, say, THHN(coarse). unless you are running 8 million watts of electrical crap you wont need to worry about heat from amp draw. clean connections, good grounds (size them as you would + wire), and good wire and you're all set. and yes you can use welding cable.
 
#28 ·
Interesting topic for sure. I have used welding cable for remote location of a large dump truck type battery in my pickup truck box(enclosed in a custom containing box with wood lining)for use in very cold winter to start without fail. What I did have happen is corrosion where the battery connectors connect to the cables(seemingly no physical corrosive elements got into the connections). The solution was a baking soda and water cleaning, shorten the cable to remove the affected cable and re connect cable ends, but adding petroliun gelly to the connections before the heat shrink wrap and on the battery posts has eleminated the corrosion..Just my thoughts. Den
 
#35 · (Edited)
Your problem with corrosion is likely caused by the venting of hydrogen gas (and / or hydrogen sulfide) and it being trapped inside a more-or-less airtight container. If you were to attach a tube to the battery vent and run it to the outside of your battery compartment, I think you'd eliminate the problem.


Dorman #924-254, NAPA #600-3574
I'm not positive on this, but I think that the round adapter do-hickey (thats a technical term, LOL) is used to adapt a battery that has an oval-shaped vent near the top of the battery. Venting a lead-acid battery in ANY enclosed space is a very good idea, as that hydrogen gas is extremely explosive! (Remember the Hindenburg?)

Also ... make sure that you are using resin-core solder (NOT acid-core) on any soldered connections. There is also an aerosol "battery protectant" spray that you can use to seal up the post-to-terminal connections.


Permatex #SA9
 
#29 ·
The idea of using a large gauge wire for a trunk mounted battery is to reduce the voltage drop. Will a 4gauge wire make the connection without burning up - probably, but the voltage drop is almost 1 1/2 volts over 15 feet, versus a drop of only .6 volts with 1/0 gauge. The sizing is to handle peak load (starting).
 
#30 ·
math samples

The battery brand has nothing to do with the wire gauge. The wire size is determined by the starting needs of the engine (ampere load) at a given ambient temperature, and the battery that is properly rated for the job expressed as (CCA) cold cranking amps.
We will assume that in a climate of (0*), a big cube high compression engine the CCA could be 400 amps or more.
The formula is Vdrop=2xLxRkxI/1000 or more clearly expressed as - voltage drop of the conductor = 2xdistance from the battery to the load x 1000 foot resistance of the conductor x load in amps divided by 1000.
Still with me? Good.
Ok - using 400 amps as a load.
And using 10 feet as a conductor distance.
And for #4 copper use - .308 ohms per 1000 feet. And for 1/0 copper use - .122 ohms per 1000 feet.
NOTE -- resistance numbers are from the NEC tables Chapter 9, table 8 conductor properties.

2x10x.308x400/1000= 2.46 volts dropped using #4 copper
and
2x10x.122x400/1000=.976 volts dropped using 1/0 copper.

I hope that somewhat demonstrates the ranges of conductors used for motor starting.

vicrod
 
#31 ·
Getting technical on wire

This was going back in time but the wire I used was 1 ott for sure over 10 feet of cable, the cranking was heating up smaller wires and over kill makes me happy. Again big battery, big motor and very cold weather starting. I only mentioned my situation as the corrosion ticked me off after all the work hooking up those nice jucy cables and quality cable ends. It did take over a year before I noticed the problem and now always add the petroiun jelly to any connection. If memory serves me for the repair I crimped the new ends,,no flux, no heat except to shrink the heat shrink wrap.
 
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