front to rear neg. wire runs ????'s

[tommyk90]

agreed, ill take tommyk's advise over some newbs anyday. until other proof is brought to the table.

Just because I have more posts than him doesn't make him a n00b.

So before you pass judgement I'd like to see him respond. If I'm wrong, I'm wrong. I have no problem with that. We all learn in the end.

[jockhater2]

@tommyk90 ;
thanks for taking the time to type up your posts. I read all of them. Even the lengthy ones. It helped me grasp and understand current/electricity a little more.

I am glad I went with the "more is better" group. I wouldn't trust my cars 21 year old rusted frame to be a good ground.

[tommyk90]

@tommyk90 ;
thanks for taking the time to type up your posts. I read all of them. Even the lengthy ones. It helped me grasp and understand current/electricity a little more.

I am glad I went with the "more is better" group. I wouldn't trust my cars 21 year old rusted frame to be a good ground.

I know exactly what you mean. My s-10 has seen better days as well. Even with a full frame (and frame grounds) I decided that negative runs were a necessity. Though I also have 2 batteries and a 340 amp alt under the hood. I'm also pulling 800+ amps so frame only was out of the question.

[jockhater2]

I know exactly what you mean. My s-10 has seen better days as well. Even with a full frame (and frame grounds) I decided that negative runs were a necessity. Though I also have 2 batteries and a 340 amp alt under the hood. I'm also pulling 800+ amps so frame only was out of the question.

It really makes sense. I wouldn't trust steel anyways as a conductor. It's mostly Iron, chrome, nickel, and then small percentages of other things. Those are all crappy conductors.

I went with the "more" group because I was told to. And I like to overkill things. Who knows what the future brings. Better than having to take my car apart again and runs when I could have done it all the 1st time. Besides. Wire can always be taken out and used in other builds. It makes sense to just go with more.

What really got to me. Was when you talked about how people who run there systems off of a rear battery bank. It makes a lot of sense that they will not notice any improvements.
I think running a system off of nothing butt batteries sounds kind of dumb. Just my opinion.

[gckless]

It really makes sense. I wouldn't trust steel anyways as a conductor. It's mostly Iron, chrome, nickel, and then small percentages of other things. Those are all crappy conductors.

I went with the "more" group because I was told to. And I like to overkill things. Who knows what the future brings. Better than having to take my car apart again and runs when I could have done it all the 1st time. Besides. Wire can always be taken out and used in other builds. It makes sense to just go with more.

What really got to me. Was when you talked about how people who run there systems off of a rear battery bank. It makes a lot of sense that they will not notice any improvements.
I think running a system off of nothing butt batteries sounds kind of dumb. Just my opinion.

For a daily driver, yes. For someone doing 3 second burps, not so much.

[tommyk90]

It really makes sense. I wouldn't trust steel anyways as a conductor. It's mostly Iron, chrome, nickel, and then small percentages of other things. Those are all crappy conductors.

I went with the "more" group because I was told to. And I like to overkill things. Who knows what the future brings. Better than having to take my car apart again and runs when I could have done it all the 1st time. Besides. Wire can always be taken out and used in other builds. It makes sense to just go with more.

What really got to me. Was when you talked about how people who run there systems off of a rear battery bank. It makes a lot of sense that they will not notice any improvements.
I think running a system off of nothing butt batteries sounds kind of dumb. Just my opinion.

Well depending on the vehicle and setup, most people don't have much of a choice but to run a large bank in the back.

For instance, since I compete in many "street" or "stock" style SPL classes I'm limited to one alternator. Running 9000+ watts on one alt is going to require a large battery bank, which I have. The best possible scenario would be to have enough alternator amperage to run all the amps in your vehicle, but this is highly unlikely for various reasons, space being the biggest issue.

The point I was trying to get across is that if a majority of your capacity is in the rear, then needing a lot of wire up to the front isn't necessary since you aren't relying heavily on your front battery or alternator to supply current when you're playing your system. Once your alt is maxed out then you're relying on your battery bank anyways. This is why 2 runs to the front will suffice for most people because of the capacity in the front versus what they have in the back.

Now if that role is reversed then the opposite would hold true. Example: A guy has 2 alternators and 2 batteries in the front and only 2 batteries in the back. Logic would say that a majority of the amperage would need to be pulled from the front because that's where the most amperage capacity lies. This is where multiple runs of each is in order. He's relying on whats under the hood versus what's in the back.

Really, the sum of it is this. If you can afford it and fit it, do it. Like you said, you never know what your system is going to be like down the road. May as well prepare for it now just in case.

[jockhater2]

Well depending on the vehicle and setup, most people don't have much of a choice but to run a large bank in the back.

For instance, since I compete in many "street" or "stock" style SPL classes I'm limited to one alternator. Running 9000+ watts on one alt is going to require a large battery bank, which I have. The best possible scenario would be to have enough alternator amperage to run all the amps in your vehicle, but this is highly unlikely for various reasons, space being the biggest issue.

The point I was trying to get across is that if a majority of your capacity is in the rear, then needing a lot of wire up to the front isn't necessary since you aren't relying heavily on your front battery or alternator to supply current when you're playing your system. Once your alt is maxed out then you're relying on your battery bank anyways. This is why 2 runs to the front will suffice for most people because of the capacity in the front versus what they have in the back.

Now if that role is reversed then the opposite would hold true. Example: A guy has 2 alternators and 2 batteries in the front and only 2 batteries in the back. Logic would say that a majority of the amperage would need to be pulled from the front because that's where the most amperage capacity lies. This is where multiple runs of each is in order. He's relying on whats under the hood versus what's in the back.

Really, the sum of it is this. If you can afford it and fit it, do it. Like you said, you never know what your system is going to be like down the road. May as well prepare for it now just in case.

Oh. Well of course in SPL set ups that makes sense. Absolutely.

I have a small 1.8L 4 cyl. With plenty of room after I removed my A/C and all of the lines. I already had my friend make brackets to mount an alternator that is meant for a yukon in my jetta. Next goal is. Using that empty A/C spot for a 2nd yukon alternator.

I am very glad I did 3 runs. Because I know that 680amps of current would be bottle necked by 2 runs. Even though I shouldn't technically be pulling 680amps on music. It will help those red lights that I am constantly sitting at. Maybe I won't have to look like an idiot sitting there holding my throttle at 2000.

Can you explain how efficiency on amplifiers work?
Like if an amp is 80% efficient and makes 1,000 watts. Which whould be 100 amps. Does that mean it actually needs 120 amps to make 1,000 watts?

[tommyk90]

Can you explain how efficiency on amplifiers work?
Like if an amp is 80% efficient and makes 1,000 watts. Which whould be 100 amps. Does that mean it actually needs 120 amps to make 1,000 watts?

That is the basic idea, yes. Not quite 100% accurate like that do to amp idle draw, voltage, heat, etc., but that is the general idea.

Voltage is the other determining factor in that equation. Higher voltage=less amperage for the same amount of wattage. Thus why SPL guys run 16v batteries and huge banks of alternators. And thus why keeping your voltage up is good for a daily driver as well. Less strain on your electrical system and the amplifier itself.

[jockhater2]

That is the basic idea, yes. Not quite 100% accurate like that do to amp idle draw, voltage, heat, etc., but that is the general idea.

Voltage is the other determining factor in that equation. Higher voltage=less amperage for the same amount of wattage. Thus why SPL guys run 16v batteries and huge banks of alternators. And thus why keeping your voltage up is good for a daily driver as well. Less strain on your electrical system and the amplifier itself.

Ohhhh. Ok. Well then I definitely want 2 add a 2nd alternator. My current amp should draw 500amps and I am adding a audison lrx 6.9k that should draw about 100amps. Plus the obvious electrical of the car itself.

I looked into upping the voltage. But it's best left for the experienced. Plus if you run more than 15v in german cars. Usually you will fry the ECU.

Thanks again for helping me gain some more knowledge!

[tommyk90]

Ohhhh. Ok. Well then I definitely want 2 add a 2nd alternator. My current amp should draw 500amps and I am adding a audison lrx 6.9k that should draw about 100amps. Plus the obvious electrical of the car itself.

I looked into upping the voltage. But it's best left for the experienced. Plus if you run more than 15v in german cars. Usually you will fry the ECU.

Thanks again for helping me gain some more knowledge!

Don't worry about going super high with the voltage. 14.5-14.7 is perfectly acceptable. Really, anything about 14v is good.

[jockhater2]

Don't worry about going super high with the voltage. 14.5-14.7 is perfectly acceptable. Really, anything about 14v is good.

That part I do understand. My voltage right now dips to 13.5 which I know is really good. But I haven't added the mids/high amp yet. And that wasn't with heat on and headlights on.

[mlstrass]

cool story

You don't have a fuggin clue kid, it's rather obvious

[mlstrass]

agreed, ill take tommyk's advise over some newbs anyday. until other proof is brought to the table.

Careful kid TimmyK is kinda skinny, so I'm not sure he'll be able to walk properly with you hangin off his sack like that

[keep_hope_alive]

Thanks @tommyk90 ; that was a good explanation.

To elaborate - what we really care about is voltage drop. we care about that because most amps will produce less power with less supply voltage. voltage drop can occur on both power wire and ground wire. as mentioned, we are trying to complete a circuit.

"load a ground" means to pull current through it, so voltage drop can be measured. a standard DMM is not accurate enough to measure ground resistance (inaccurate at low resistances). there are separate tools for that, or you can just pull a known current and measure voltage drop and calculate it.

There are no "hard and fast" rules, but if your expected draw from the front is less than 200A, you are probably fine with using good steel (not necessarily the body). if you start to run parallel sets and multiple alts, run dedicated grounds.

It certainly won't hurt to run dedicated grounds, and in reality, resistance will be less since you have continuous copper from back to front and not separate pieces of welded steel.

The more I think about it, the more I think that dedicated grounds are a good idea for anyone... lowering resistance is the goal, and each connection contributes for the majority of resistance. More importantly is the resistivity of metals...

The Resistivity of Copper is 1.712
The Resistivity of Steel is 11.8
The Resistivity of Aluminum is 2.709

Resistivity is 10^(-8) ohm-m @25 deg C
Lower resistivity means better conductance.
Taken from "CRC Handbook of Chemistry and Physics, 57th Edition, 1976-1977, CRC Press, p. F167-168; CRC Handbook of Chemistry and Physics, 90th Edition, 2009-2010, CRC Press, p. 12-14, p. 15-37"