minimum size of battery cable

[chevy art]

both my buddies are runnung custom made 200 amp alternators and they each burned one up that needed to be rebuilt. they both use 10 gauge wire from front of car to battery in the trunk as their battery cables. i dont agree with them about this cable size and think the minimum cable should be a # 6 cable. one has the 3 prong plug in harness, and the other has a 1 wire alternator setup.any thoughts on this, and if the cables are definitely too small, how and why would this burn up the alternator.have not had one of them tested yet to really see if it burned up, battery just went dead starting a run at the track, and with all the accessories on the volts just kept dropping down below 12 volts and car hotter and misfired. any thoughts om this would be appreciated thanks art

[In-Tech]

10 gauge, really? This chart will get you in the ballpark. Always overbuild wire size unless weight is a factor.

WireSize.jpg

[user-23911]

both my buddies are running custom made 200 amp alternators and they each burned one up that needed to be rebuilt.

Lemons?


Cable size has nothing to do with alternators burning up.

If the battery is in the back of the car and the cable is too thin, you'll have starting problems. The starter motor will be struggling.

If the alternator is working correctly and it's fitted correctly, it'll work regardless.
Correctly......that's another problem.


But "custom built" and "200A"tends to ring alarm bells.


An alternator's output current is dependent on the alternator RPM. In order to get more current, spin it faster.
Spinning too fast makes it fail.


Maybe what you should be asking is.........."what mods were done to it to make 200A" and "how many RPM does it need to spin to, to get 200A" and "at what voltage does it make 200A at"?

[Bradley67]

This ^^^^^^
I use Zero gauge from starter to trunk battery.

[David Redszus]

Cable size has nothing to do with alternators burning up.

If the battery is in the back of the car and the cable is too thin, you'll have starting problems. The starter motor will be struggling.

Absolutely correct. Alternators do not start engines; batteries do that.

If a starter motor produces 2 HP, that is equivalent to 1500 watts.
If the battery lead length is 10 ft or more, A 0 size cable should be used per the posted chart.

Why did the alternator fail? If a battery does not take a charge, the alternator will attempt to push more current to the battery and cause overheating of the alternator.

[RCJ]

I believe the OP means the wire from the alt. to the battery is 10gauge not the battery cable is 10 gauge.He raise a good point thou, how can a 10 gauge wire work on a 200 amp system. The wire should be melting.

[MT Jeff]

Why not tie the alternator into the battery cable at the solenoid and use the battery cable to carry the current. You would still need more than 10ga though. 4ga would work. I would think.

[Truckedup]

I believe the OP means the wire from the alt. to the battery is 10gauge not the battery cable is 10 gauge.He raise a good point thou, how can a 10 gauge wire work on a 200 amp system. The wire should be melting.

It probably would melt if the alternator had to produce 100 amps continuously....Keep in mind that GM used a #10 wire for 60 amp alternators for many years...

[chevy art]

thanks for all the replies. i will show this to my friend tomorrow and he can take it from there. also bringing the alternator back to the rebuilder to have him check it out and test it. im not sure if one of the members asked about the 10 guage wire my buddy has in the car. it runs from the alternator to the battery and brings the juice to the battery. think i said that right art

[John Wallace]

He should have a power connection/buss at the front?
The wire from the alternator goes to it, and the big battery cable goes to the battery in back.
The main power runs from that connection at front, like starter, lights etc.

Use relays also.

[gnicholson]

thats crazy. even a stock older 60 amp altennator would havw a serious voltage drop across a 10 amp wire that long when full fielded. You need at least 0 gauge cable to the battery whether you do it through the starter cable or a standalone cable if you are running a battery cutoff switch. With two hundred amp alternator a discharged battery and a 10 gauge cable it will act like a fusible link and burn in half

[David Redszus]

thats crazy. even a stock older 60 amp altennator would havw a serious voltage drop across a 10 amp wire that long when full fielded. You need at least 0 gauge cable to the battery whether you do it through the starter cable or a standalone cable if you are running a battery cutoff switch. With two hundred amp alternator a discharged battery and a 10 gauge cable it will act like a fusible link and burn in half

A 200 amp alternator and a discharged battery, with only 5 ft of #10 solid copper wire will result in a voltage drop of 9.57%. The accepted maximum voltage drop is 2%. You do have a fusible link.

[user-23911]

But a 200A alternator won't make 200A until you've got it spinning at "full" RPM and you're NOT going to put 200A into a discharged battery.....you'll kill it (the battery).
You're not going to get the engine started with a fully discharged battery, so it's pretty much an impossible situation to get into.


So back to the first question.
Under what conditions does it make 200A.

It probably doesn't.
Ever.

[Truckedup]

But a 200A alternator won't make 200A until you've got it spinning at "full" RPM and you're NOT going to put 200A into a discharged battery.....you'll kill it (the battery).
You're not going to get the engine started with a fully discharged battery, so it's pretty much an impossible situation to get into.


So back to the first question.
Under what conditions does it make 200A.

It probably doesn't.
Ever.

I used to rebuild truck and bus alternators in the late 1970's. 100-120 amps was a big alternator then...For bench testing a large variable "Resistor" tester was the load. The alternator/generator was belt driven by an 8 HP gas engine..A bus with lights on and the four heat blowers was a 80 amp draw...Modern vehicles have what? A 120 amp alternators? Probably to maintain about 60 amps at idle with the lights, AC and other loads...

[gnicholson]

But a 200A alternator won't make 200A until you've got it spinning at "full" RPM and you're NOT going to put 200A into a discharged battery.....you'll kill it (the battery).
You're not going to get the engine started with a fully discharged battery, so it's pretty much an impossible situation to get into.


So back to the first question.
Under what conditions does it make 200A.

It probably doesn't.
Ever.

my point was its to small even for a muxh smaller alternator. a 60 amp load would require a 4 guage cable that length. Remember it's not just the battery that's receiving the amperage. It's all of the accessories. That's why they made these huge alternators.... all of the electric draw from all of these accessories like big stereo systems etc. gotta keep the voltage over 14. Even though it would probably never produce that much amperage in the vehicle the cable should still be sized for the length and the amperage the alternator is capable of producing