Are current ratings BS?

[helotaxi 5,000+ posts]

The battery serves one other important function in the car's electrical system and that is as a filter. Get rid of the battery and the car's computer would have some issues with DC ripple and may not work correctly.

The automakers use the chassis as a part of the circuit for all the electrics in the car out of convenience. Boats work on a 12V DC system just like a car and car amps can and are used in boats. Try "grounding" an amp to the fiberglass hull of a boat. Everything in a boat is wired back to the battery.

The reason to run a wire back to the battery instead of using the chassis in a high power install is that the chassis is really a pretty crappy conductor.

As far as voltage and rating, wire application charts are based off a finite voltage drop but this is different than wire rating. The charts take length into account, ratings don't.

 

[ocdadhd]

The battery serves one other important function in the car's electrical system and that is as a filter. Get rid of the battery and the car's computer would have some issues with DC ripple and may not work correctly.
The automakers use the chassis as a part of the circuit for all the electrics in the car out of convenience. Boats work on a 12V DC system just like a car and car amps can and are used in boats. Try "grounding" an amp to the fiberglass hull of a boat. Everything in a boat is wired back to the battery.

The reason to run a wire back to the battery instead of using the chassis in a high power install is that the chassis is really a pretty crappy conductor.

As far as voltage and rating, wire application charts are based off a finite voltage drop but this is different than wire rating. The charts take length into account, ratings don't.

If you find a point on the frame & ground it with 0 resistance, why would you run wire all the way back to the battery.

 

[CHEMMINS 10+ year member]

There is no such thing as a frame ground with 0 resistance. Look at the resistance of different metals. You frame has way more resistance than a straight to batt copper line.

 

[CHEMMINS 10+ year member]

Think about it...the current has to flow through the amp, through your short wire, then through your high resistance frame, then through another piece of wire to get back to the point of origin to complete a circuit.

 

[helotaxi 5,000+ posts]

The guys at JL Audio did some testing years ago and the vehicle they tested had about the same resistance as a single run of 4a wire.

 

[CHEMMINS 10+ year member]

Prolly back when vehicles were actually made of metal, not todays composites and thin gauge metals.

 

[ocdadhd]

Prolly back when vehicles were actually made of metal, not todays composites and thin gauge metals.

My '00 Z28 is thin metal & the body is actually fiberglass.......however, my '00 Grand Cherokee is SOLID. I have almost 0 resistance in my ground, I measured it.

 

[ocdadhd]

Prolly back when vehicles were actually made of metal, not todays composites and thin gauge metals.

The actual frame, not the body. Well, maybe except for Toyota---they use recycled steel.

 

[helotaxi 5,000+ posts]

Most cars are unibodies and thus don't have a frame. Depending on the current draw of the system, if the resistance is measurable with a normal DMM, it's too high. Most DMMs will only measure to 0.01 ohms which with a 100a current draw would be a 1v drop.

 

[CHEMMINS 10+ year member]

Yup....you should never get any resistance measurement. Saying you got almost 0, means you read something, and as HT said....0.01 ohms is 1v, which is huge.....7% loss at 14v

 

[Buck 5,000+ posts]

So, is there any verdict?

 

[PIITB Wut Wut 10+ year member]

yes....

take 2 batteries

take 3 pieces of 1/0 wire

attach the grounds and hots so the batts are connected and connect a 3rd line to just one batts positive...

take dmm and place on peak voltage and stab into pos and neg wires

take clamp meter and put on peak voltage and attach to unhook pos line

touch unhooked pos line to ground... repeat with different lengths.... goodluck

 

[Buck 5,000+ posts]

yes....
take 2 batteries

take 3 pieces of 1/0 wire

attach the grounds and hots so the batts are connected and connect a 3rd line to just one batts positive...

take dmm and place on peak voltage and stab into pos and neg wires

take clamp meter and put on peak voltage and attach to unhook pos line

touch unhooked pos line to ground... repeat with different lengths.... goodluck

Did you get your username from that gay *** video with the black dude in it?

 

[jrouter76 10+ year member]

So instead of grounding your amps in the back of the trunk with a 2-3 foot wire(1/0) it would be better to run a 1/0 from the battery(neg) back to a fuse distro for my amps correct ?

 

[emilimo701 10+ year member]

True, but voltage is a concern really, cause 300amps at 12v is a lot different than 300 amps at say 600v. When they test these cables what is the testing voltage?

no, it's not. you really should be certain you know what you're talking about before you give technical advice like this