Amp Power Wiring Question - Chevy Impala SS Forum
 
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post #1 of 8 (permalink) Old 01-12-2016, 01:37 AM Thread Starter
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Amp Power Wiring Question

I'm hoping soon to be able to install my old subwoofer and amp combo and I want to get another amp (4 channel) to power the front and rear speakers. I have an amp wiring kit that came with a 4 gauge power wire that I was planning on using for this. The amp I have is the Rockford Fosgate P500-1bd, and I want to get the p400-4 (or similar) for the regular speakers.
My question is, will the 4 gauge power wire be good to run to a distribution block in the trunk and the two amps off of it?
Also, my car is bagged and I have a smaller gauge power wire running to the trunk to run the compressor. I was thinking of having all three of these connected to the distribution block (with the compressor having an inline fuse between it and the block.)
Should this work?
Any info is appreciated!
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post #2 of 8 (permalink) Old 01-12-2016, 12:35 PM
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Many factors many opinions

Second question first. In theory you can use the amps and compressor together. Practically you will have to make sure the compressor does not make electrical noise, or if the amps and audio cables can reject compressor electrical noise. In the old days we fought against the alternator and the heater blower. DC motors spark at the brushes and make noise. When they start they surge high current and spark at the relay or switch. New amps with good audio cables should reject this.

Is 4 ga good enough? How far are you running it and how much current(amps) are you running through it?

Assuming 25 feet and 100 amps continuous load (a lot of driving lights) you should go heavier. Car stereo systems do not draw continuous loads but peak loads from the low frequency audio. For me 4 ga might be OK for you if you play loud all the time with the bass high heaver wire is needed.

Good amps have capacitors in them that will give you clean audio when the load peaks high. Heavy wire will reduce the times they have to work.

You also have to have a good ground. Good wire and connection to the frame at both ends. If you run a separate ground wire you have double the gauge of both wires (positive and negative) to allow for the voltage drop in both wires. 25 feet positive plus 25 feet negative is a 50 foot run on the charts. Most audio installers consider the frame heavy enough not to drop the voltage. The down side is any rust between the wire lug and the frame will drop voltage.

I would use heavier wire than the 4 ga.

Try this chart. http://assets.bluesea.com/files/reso...ence/20010.pdf

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post #3 of 8 (permalink) Old 01-12-2016, 05:49 PM Thread Starter
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I'll probably just run a separate power wire for the amps to reduce the risk of noise.

I'd definitely like to get a bigger gauge wire but I just got this kit as a gift and I'm not sure if I can exchange it.

I had emailed Rockford Fosgate before you had responded and they said the 4 awg should be fine.

Hmmm
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post #4 of 8 (permalink) Old 01-12-2016, 09:18 PM
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100 Amp guess

100 Amp was a guess. If P500-1bd is 500 W and p400-4 is 400 W = 900 W devide by12 Volt = 75 Amp X 1.3 (amplifier wasted power) = 97.5 Amp

Post RMS and Peak wattage for both amps (all channels) and what fuses they use and the numbers will be more correct. I do not have the time to research your amps.

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post #5 of 8 (permalink) Old 01-13-2016, 01:28 AM Thread Starter
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The P500-1bd says
RMS: 500 Watts x 1 @ 1-Ohm (which is how I run it)
Info here (http://www.rockfordfosgate.com/produ...tails/p500-1bd)
The newer version of this amp gives max and average current draws at:
(http://www.rockfordfosgate.com/produ...tails/p500x1bd)
Average: 35 A
Max: 70 A

The P400X4 (http://www.rockfordfosgate.com/products/details/p400x4)
RMS: 50x4 @ 4-Ohm
Average: 30 A
Max: 60 A

I hope that's what you were asking about.

Thanks for all the help!
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post #6 of 8 (permalink) Old 01-13-2016, 11:38 AM
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130 A Peak

"I had emailed Rockford Fosgate before you had responded and they said the 4 awg should be fine."
This would be OK for ONE amplifier.

So if you look at the chart 120 Amp 50 feet (25 pos, 25 neg) 10% voltage loss it recommends 2 ga much bigger than your 4 ga kit.

If you run the volume at MAX all the time you would want the 3% table which recommends 4/0 ga. This is a massive task to safely route in a car. The head ache of a second battery would be easier.

Fuse the positive at the battery. (150 amp?) This is fire protection not amplifier protection. Despite the miss information any good wire will work. My first car used a booster cable. Looking back at it I do not think there was enough plastic to protect the wire but you could find a deal on a quality one. Welding cables are a good choice for protected wire but need to be kept away from the engine and exhaust.

If you poke around this site you will find people have run the cable through the firewall on the driver's and passenger side. Some run it under. If you go under It should be protected and anchored alot.

Amps should be placed so the fan air moves around and does not suck back in the hot air it just sent out.

The speaker wire is just as important. 14 ga or 12 ga for the speakers and the shortest biggest wire you can afford for the woofer.

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post #7 of 8 (permalink) Old 01-16-2016, 05:49 AM Thread Starter
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Wouldn't it be better running the power wire from the battery to the trunk and then the ground from the amp to a close by grounding location, not back to the battery?

I contacted the company I got the wire kit from and it seems like they'll exchange it.
I'll have to pay the difference for the bigger wire, but I'd rather be safe.
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post #8 of 8 (permalink) Old 01-16-2016, 11:48 AM
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You need a good ground.

"Wouldn't it be better running the power wire from the battery to the trunk and then the ground from the amp to a close by grounding location, not back to the battery?"

There is no close grounding location. The only factory ground wire that can handle this power is to the engine block. If you check the FSM you will find no direct ground connection to the frame. The factory ground wire to the body is rated for the factory power loads. I would never use the body as a connection for this much power. You are pulling enough power to weld metal. A connection that goes bad will melt sheet metal.

You can find a thread about the battery to sheet metal ground failing and all the problems it can cause.

You can connect the battery to the frame then the frame to a power block. It is hard to stop the frame connections from rusting. If you want to do this once I recommend a ground cable unless you live in a desert.

You are headed into the high power accessory alley. When you come out the other side your wallet will be much lighter. First you install the electronics and cables. Then you need a larger alternator and wire harness to the battery. Factory HD alternator is 140 amp. Most of this power is used by the cooling fans and AC. These cars were never made for this kind of power use.

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