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which to use for a trunk mount battery setup?

  • welding cable

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Discussion Starter #1
as i am coming close to be needing to power a certain 69 cougar. i need to know what you guys and girls are using for your trunk mount batterys. I have always heard welding cable is cheaper and stronger and more conductive than battery cable. What have you guys and girls used? What are the pros and cons?
justin
 

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Even with my engine bay mounted battery I run either 1- or 0-gauge battery cables. Remember that you need four cables. Battery to solenoid, solenoid to starter, battery to chassis ground and (here's the one most people forget) engine to chassis. Remember that you need a complete circuit. If you forget that last cable, the current tries to find other pathways that you might not like - like your throttle cable or gauge wiring harness! :eek7: NOT a good thing!!! You laugh, but I've seen a guy's throttle cable literally smoking when he was cranking the motor over since that was the only ground 'wire'.

Remember, your starting (or charging) circuits are only as good as the weakest link - or the smallest gauge wire in the circuit. Our Cougar's factory negative battery cable had a lug in the middle of it that bolted to one of the voltage regulator mounting screws. That in essence made that one cable the battery-chassis and the engine-chassis ground. This also ensures that your voltage regulator has a good ground so you don't have charging problems, 'flickering lights' or problems with your sequentials working as they should.... Parts store replacement cables don't have that feature. If you rely on the 14-ga wire pigtail on the replacement battery cable as a chassis ground, how much current do you think you can get through that? That's why I use the four full-size battery cables.
 

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Discussion Starter #3
yes milo i am very aware of needing all 4 cables! in fact i have new ground straps as well, i have a 2 gauge ground cable for the engine to frame made already
 

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Justin I still have some of this: http://www.mercurycougar.net/forums/showthread.php?44713-2-Guage-Wire&highlight=cable

the bigger the cable the lower the voltage drop.....just run from relay to cut-off (if using) to batt+ then from batt- to grd on frame. Of course the cut-off must be external for some racing requirements, but you will likely want one even if you don't plan to race just for safety/convenience. You could locate it inconspicuously in the trunk otherwise. PM me if you want any - got plenty.

Mike
 

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use 2/0 fine wire welding cable---mc master/carr sells plated bronze cable ends with a solder pellet already in the end---they also sell shrink tube with adhesive inside to protect the solder joint---make sure you order the correct size end for the wire you'r using---also pos or neg terminals and r/h or l/h
i used 2/0 with the front mounted battery and # 6 for the alt charge line---if you have an old 6 volt car , changing to 2/0 cables can be the best thing you'll ever do to promote better starting
doctordesoto
 

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I used the welding cable as well on all mine. It was originally recommended to me by a well known hot rod shop up here.
 

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Cable is cable. What makes a difference is the gauge size, and the wire construction.

Larger wire gauges (lower number is larger) have lower resistance per foot. The total resistance of the wire and the return path through the chassis of the car, will determine the voltage drop. The speed at which the starter motor turns is a function of the voltage.

Some cable may be made of aluminum or CCA (Copper Clad Aluminum). You don't want to use this stuff. It looks big, but has MUCH higher resitance. The number of strands determines how easy it is to bend the wire. More strands means it is easier to go around corners. The wire gets its AWG rating based on resistance per foot so a 4G wire with 1600 strands has the same capacity as a 4G wire with 12 strands.

The insulator is very important. You want cable rated for 105 degrees C. Cables get hot and you don't want the insulator to melt. The ampacity of the cable, (a measure of how much current you can run through the cable safely), is dependent, in part, on the melting point of the insulator.

Keep in mind that the car, when running does not run off the battery, it runs off the output of the alternator. The battery is actually just another load on the alternator as it is being charged. The battery charging current is only a small fraction of the current that the battery puts out when turning the starter. The battery is charged through the same wire as its output.

When you move the battery, the main thing you have to do is to keep the resistance of the battery to starter cable the same as the shorter cable you are replacing. IF you can make really good connections to the chassis, it will have a lower resistance than just about any cable. This will require you to make up a short cable running from the chassis to the original ground location on the block. All of the connections must be very good. If you are in doubt about the connections, then you should run a ground cable from the battery to the original ground point on the block, where the original battery cable was connected.

There is no need to change the cable from the starter solenoid the to starter motor. Moving the battery has no effect on this part of the circuit.

Remember, it is Ohms LAW, not ohms suggestion.
 

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the basic concept of xr7g428 is correct but i doiffer with two points :the car does run off the battery if the load exceeds the alt output---in the winter and in the rain , my wifes sable would turn up a dead battery after 4 days of weather--reason the current draw of all the stuff(lights,heater,wipers,defroster,ect)excceded the 75 amp output on the alt--the following year ford went to 100 amp alt
the second item is using the std starter cable---the sys is only as good as the weakest link--we used 2/0 everywhere , including the starter cable---the fine welding wire has another advantage over a 12 conductor cable---break one conductor on the 12 cond cable and you lost 8 %--loose one on a 1600 conductor you have lost less than 1/10 of one percent
doctordesoto
 

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I am running the stuff that Mike (Bad69cat) is selling. Granted, I have my starter solenoind inside the car, so the main cable is much shorter. Also, my solenoid to starter cable is only about a foot or so long, even with going through the firewall. I have a 4 gauge wire running from the 3G alternator to the solenoid inside the car.
 

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Discussion Starter #11
thanks for all the input guys. badcat you got pm ! . bill, i was/am a mechanic by trade(other than being parts dude) that was quite the classroom flashback!

btw guys, electrically the only thing original on this car when i am done will be the main looms, everything else is being moved and modified . efi+ 3g+ newer fuse panel+ eventuall electric fan(s) +stereo that will go bump in the night!
 

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We took a current reading on a slightly built 350 Chevy and saw it was pulling 463 amps! of current to start. If you try to pull that kind of current through a small wire the voltage drop to the starter will be very noticeable and the starter will turn slowly if at all.
 

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it appears that with all the new electronics that grounds are a real issue----i put a spal pwm computer to run the electric fans .the instructions called for a chassis ground---even with a 2/0 engine to chassis line the system would not work correctly until i ran a 6 ga wire from the neg bat terminal to the point on the chassis where we were grounding the computer---now the pwm works exactly as advertised
doctordesoto
 

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Discussion Starter #14
i plan on doing block to ground, head to ground. dash board to ground. and battery to ground.
 
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