8 Gauge wire to battery and 130 amp alternator?
 

I normally like to run a 00 wire up to the front and pull everything off a solenoid up front. This racer is adament that he wants the starter solenoid in the trunk (65 Tempest) with separate wires for everything run to the front so that the starter cable is dead except when cranking. Currently has an 8 guage dedicated wire from alternator to trunk battery, and I see that 8 gauge carries about 55 amps on a good day. Planned alternator is a CS130D that can put out 130 amps maximum and will still be capable of 90 amps at 1,200 RPM idle - at least at the alternator. Is there another solution other than running a larger cable just for the charging circuit?

I was reading somewhere that smaller wire size in itself will limit charging amperage but don't want to melt a wire finding out the theory doesn't work. At the moment I'm thinking about protecting the 8 gauge wire with a 60 amp fuse at the battery.

Ive wired a few that way, with the starter solenoid in the back so the main cable is only hot while cranking. I use 6 gauge from the shut-off switch to the alternator, with a pair of 80A fuses in parallel. The car feed, I use 6GA with a 200A breaker, feeding a terminal block that I use to feed vehicle power. I mount the breaker on a vibration proof mount so it won't trip from tire shake, etc. It's a little more work and more parts, but if the customer is paying, they get what they ask for within reason.

Starting to realize that the 8 gauge was too light. Wonder if we just doubled up with another 8 gauge wire in parallel with the one in place now if that would be enough?

8 gauge is fine; Batt does not need 55 Amp (like ever) from Alternator. The Alt will power items mostly in the front-end.

I use a 3 ga wire from my alternator to my battery in the trunk and pull about 65 A with all electrical devices on.

How many amps does your alternator give your battery. What is normal ?
Reason I ask is because I got into a back and fourth with a manager at a chain auto parts store where he told me if your battery goes dead life from leaving a key on overnight even a 8 hour drive will not come close to charging your battery fully. His in store charger would in a hour and a half.
I kinda said he was full of it.
I was always under the under standing that a fast charge is as not as good for a battery as say a 2 amp trickle charge overnight.

My comment was for Lead-Acid battery not consuming much current while charging. They draw 2-15 Amps when impressed with 14.4 Volts.

As for LiPo, i dunno what they draw; probably less as the heat from a high current charge would likely be exciting.

Marine wire where the individual strands are tinned can flow more juice with a smaller gauge.

Not true. Marine wire tinning to prevent corrosion does not increase ampacity. Higher heat insulation & true AWG sizes lend to higher ampacity rating,

How does higher heat insulation increase ampacity?

Resistance/ft does follow the wire gauge but "Ampacity" is limited by heat dissipation. If the insulation can tolerate more heat, the wire can "safely" run hotter without melting/degrading the jacket. Doesn't mean it's smart but that's the argument. It's a rating thing.

Margin is your friend, especially when the load's performance is sensitive to voltage (like a starter motor).

You learn something new every day.

Sad thing about many 'battery cable' is they are all over the board when it comes to quality. This is why many suggest a cable size of a much larger gauge.

Rule of thumb I use when buying battery cable is it has to be clearly marked showing the type of cable it is. (generally SGT & SGX). That will ensure you have quality cable by meeting a standard. SGX has a high heat rated cover, and allows you to use pure copper, but you can run marine type tinned if you want.(As long as it's clearly marked with spec).

The tinning for marine is not for heat resistance, it's for corrosion resistance, and does have higher electrical resistance. So run one or two sizes larger than you would for SGT/SGX.

Use SGT for power run to SOL, and SGX for the start run. If you have a remote mount SOL, and put it as near to the starter as possible, a 6g or 8g for cranking will work fine. Use SGX from the SOL to starter.

The batt wire would be run to the SOL power post, as would the alt & all accessory power runs. You can run one 4g or 6g from the SOL power post to a remote post or terminal block for individual runs and to keep from loading up the SOL post (can also fuse/breaker individual runs). Keep the alt charge wire on the SOL post. If you can, use a 4g or 6g charge wire, it's recommended to be one size larger than the accessory wire, or same size from batt to power gauge.

(Make sure you're ignition key-on power wire is run to a key-on switched source.)

Charging from alt never reaches high capacities because the alt is powering the accessories while running. And of course, you want the acc power run to be as close to the alt as possible.

You NEVER use the alt to charge a low charged battery for a number of reasons. First, it would take many hours, because the accessories are using X amount of amps. Second, you can cook an alt that way (over tax the regulator, or worse). When replacing a battery w a new one, it is always recommended to fully charge the batt on a dedicated charger. The why is previously stated.

You can use a solid state high amp breaker as a protection between the batt and the SOL power wire, like this 200a waterproof unit or similar:

https://www.solar-electric.com/manua...t-breaker.html

Of course, make the breaker as close to the batt as possible.

Use quality high heat terminals, using a correct crimper, cover with double wall adhesive shrink tube. The crimp compresses the wire for full contact of all strands and prevents corrosion.

One big concern of trunk mounted batteries is the ground, especially if you are using the frame. To ensure the best contact, use a thread-sert/nut-sert on the frame. If need be, use a thru-panel post and boots.

My morning brain dump...

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Just realized I typed for nothing! Knew I should have had coffee first!

Might be able to redeem myself some by suggesting a fuse/relay distro block:

https://www.waytekwire.com/catalog/p...ini-fuse-panel

Also will comment that the charge wire should be GXL, and think 8G would work, but agree 6g is a better choice. Think GXL only goes as big as 8g, so may be forced to use SGT/SGX if you want to go 6g.


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Its per the NEC national electrical code. It can carry a higher amperage with a higher rated insulation. You also derate the amperage for ambient heat, length of runs and wire fill in conduits.

GM (and other US OEs) use GXL, TXL, SGT, and SGX wire in new cars and commercial vehicles.

Here's the GXL/TXL AWG recommendations and the battery cable AWG/AMP/Feet chart.

Also, here's the GM Electrical Best Practices doc, if you want to review it:

https://www.gmupfitter.com/wp-conten...rac_093017.pdf

Just to say, NEC doesn't provide guidance to the auto industry, although some principals apply.

SAE & NHTSA regulate automotive stuff, you can read their' docs if you really need to take a nap.


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Thank you for the information. While I was reading the latest posts my son-in-law returned with 25' of 4-gauge thin strand wire which will be the dedicated charge wire from alternator to battery. Not sure but think the alternator is a 110 amp unit. The 4 gauge will be better than the 6 or 8 gauge I was considering and that's never a bad thing.

Next point is I have always wired my (few) drag cars with a thick 00 gauge wire up to a solenoid on the firewall and branched everything off from there. This racer was talked into having the solenoid back in the trunk so the thick wire would only be hot during starting. Well that's fine and good, but he's ignoring the 4 gauge alternator wire, the 10-gauge wire to the MSD box, the 10 gauge wire to the dashboard main cutoff switch that have to be hot during running. Seems to me that all those smaller wires present more of a short risk than one well protected large cable? Also instead of having short runs up front, we've ended up going up a guage or two to compensate for the additional 15' of wire coming from the rear and that's increased the cost of the project.