Stereo/amp power and ground wires to battery.

[ntsqd]

That's exactly the kind of anecdotal detail that I specifically was not asking for.

Why does it do that when the ground wire is long? Anyone ever try a shielded cable (properly drained)? How about twisting the ground and power wires together? So far all we have is an Old Wives Tale.

A short ground wire means that the ground path is going thru spot welds and is an indirect path (read: longer) that potentially has much more resistance than the wire to the battery will have. If you're going to do that, why bother with stipulating that the ground wire needs to be the same gauge as the power wire?

 

[bronconut73]

I have cured folks radio whine by simply cutting their ground wire that they had taken all the way to the battery and providing a good/clean chassis ground.
Then take the ground wire they had ran to the battery and ground the battery to the chassis if it is not already obviously done.
I am not smart enough to tell you why that works I only know that it does.

Sometimes radio whine can be a plethora of issues ....but I often see it where a well meaning self installer ran their amp ground all the way to the battery or had their power wires and ground wire ran right next to their speaker wires or rca wires.

 

[Banjer Picker]

Feedback

ya know, we could give better advice if you'd just answer this question. If you can't then I'll quit wasting my time.

Couldn't really find any specs that referred to "input" other than "Input impedance" (Its 10kOHMs) and that the amp can take up to 50W input from the head unit. All other specs seem to be output.

The amp is a Kenwood KAC-M1824BT. If that helps any.

I'v already got it wired to the battery with a 12 gauge wire and 15A fuse for what its worth.

 

[ntsqd]

http://www.kenwood.com/usa/car/marine/kac-m1824bt/spec.html

45W X 4 / 90% (power inefficiency guess) = 200W input; 200W / 11Volts (min allowable) = 18 amps peak input.

Per: http://www.ancorproducts.com/en/resources/three-percent-voltage-drop linked previously -
A) 20 amps (@ 3% Voltage Drop) at 10 feet from the battery (20' total circuit length) = 8 gauge

B) 20 amps (@ 3% Voltage Drop) at 7.5 feet from the battery (15' total circuit length) = 10 gauge

There are charts for 10% Voltage Drop, I don't use those for electronic gear or motors.

 

[Banjer Picker]

http://www.kenwood.com/usa/car/marine/kac-m1824bt/spec.html

45W X 4 / 90% (power inefficiency guess) = 200W input; 200W / 11Volts (min allowable) = 18 amps peak input.

Per: http://www.ancorproducts.com/en/resources/three-percent-voltage-drop linked previously -
A) 20 amps (@ 3% Voltage Drop) at 10 feet from the battery (20' total circuit length) = 8 gauge

B) 20 amps (@ 3% Voltage Drop) at 7.5 feet from the battery (15' total circuit length) = 10 gauge

There are charts for 10% Voltage Drop, I don't use those for electronic gear or motors.

So, would that indicate a poor design by Kenwood that the amp comes hardwired (via wire harness) with 16 gauge power and ground wires?

 

[ntsqd]

No, it would not. They have no idea how long of a power run might be needed and they're constrained by their accountants to not make the wire any bigger than necessary. For the length of their supplied wire, 16 Ga. is fine.

The National Electric Code is unfortunately persuasive in its saying X amps = Y wire size regardless of the length of the circuit. Within their codified world it works fine, but the general assumption is that it applies universally, which it does not. DC requires different wire size than does the same volt/amps in AC, and it goes on and on. Part of the reason I use the Ancor table is because they're geared to marine DC circuits.

 

[RODRIG3911]

I looked it up for you.

The ground for the amplifier should be directed to a bare metal area of the car body, within eighteen inches of the amp’s location. Your objective is to try to ground to the main chassis or the sub frame. The most common amplifier grounding locations in a vehicle are anywhere that has a bolt directly connected to the metal chassis. However, these bolts are normally glued to keep them from unscrewing, so LockTight or mild bolt adhesive should be used to re-secure them. If you’re mounting your amplifier in the trunk, the most common ground would be the strut tower. You have to be sure to sand down any paint or rust until you see the shiny metal underneath for the best connection
Ground to chassis!!

I've installed hundreds of amps this correct way and never had a problem, but I have fixed many with whining issues that other people installed like bronco nut said

 

[ntsqd]

This still is a "How", not a "Why". "Correct way" is subjective. ALL of my Ham radios, which have RF amplifiers in them, want a direct to battery ground. They don't whine.

 

[randbjorn]

That's exactly the kind of anecdotal detail that I specifically was not asking for.

Why does it do that when the ground wire is long? Anyone ever try a shielded cable (properly drained)? How about twisting the ground and power wires together? So far all we have is an Old Wives Tale.

A short ground wire means that the ground path is going thru spot welds and is an indirect path (read: longer) that potentially has much more resistance than the wire to the battery will have. If you're going to do that, why bother with stipulating that the ground wire needs to be the same gauge as the power wire?

If your vehicles electrical system is perfoming as designed then there is absolutely no reason to run a ground back to the battery. The fact that there is NOT a large cluster of ground wires coming back to the battery from all of the electrical components installed by the manufacturer in your vehicle should tell you something. Grounding that amplifier to a paint removed bare metal surface will provide plenty of ground path for that amp unless your electrical system is sub par. Specifically there should be a ground strap from the body of your rig tied to the battery to help insure an adequate ground path. As to the question of the size of the power wire. The reason that amplifier comes with an prewired 18ga power lead is because that is all that it needs. It was designed to stuff under the dash somewhere and be tied into the constant power lead that normally feeds your radio. Most aftermarket radios have built into them the same amount of power as that amp. You ever run an 8ga power lead to your radio? It would be like running a 1" fuel line to the carburetor on your small block. If it makes you feel better, do it. As to the noise issue, both the radio and amplifier should see the same ground reference. If the amp is grounded to the battery and the radio to the body it can contribute to a ground loop issue so thats a no no. Quality shielded rca cables and good clean grounds are the best recipe for a noise free system. That being said your system will only perform as well as it weakest link (just as someone else pointed out here). Cheap or damaged components are gonna cause problems no matter how well they are installed. Hope this helps!

 

[ntsqd]

OK, ground loop picking up noise makes some sense. Why not just bring the stereo's ground to the battery too? Then you know that they've got the same ground reference and as a bonus you get max potential - no voltage drop from iffy weld conductance etc.

If you're grounding to the body, even if the body is properly grounded, you're still grounding thru welds. Arguably at low power their resistance isn't very high, but it's still there. A long time ago I learned to never, ever ground trailer lights to the trailer frame. Run a dedicated ground wire system or you WILL have problems eventually. I don't see this as being any different. Analogous to remote mounted batteries in drag cars (even though that's high current and not directly the same), never, ever use the chassis for the ground, always run a ground cable up to the engine block or starter itself. Do anything different and the car will eventually have hot start problems. BT, DT in both cases.

 

[randbjorn]

Like I said, If it makes you feel better, do it. But, If grounding directly to the battery vs. grounding to the body/chasis produces any measurable or noticeable performance difference with the parts we are discussing here, then you are going to have issues with every other electrical component that is currently grounded to the body/chasis of you're vehicle. By your logic, every other critical electrical component (ignition system, fuel pump,pcm's tcm' etc.) should be grounded directly to the battery too. Personally, Id rather make sure that the entire electrical system in my eb functions as it should to help insure optimum performance of every electrical component.

 

[ntsqd]

Not by my logic, no - not everything. You're extending a concept beyond it's intent. But some things, yes. Particularly those with amplifiers. No seems to get that mobile ham radios want a direct battery ground. Every one of them. Without known exception. Why is that? My guess is that they have proper noise filtering and stereo amps can't be bothered with that expense. So band-aid fixes have become the "correct" way to wire them.

 

[randbjorn]

If you can't answer for yourself why a ham radio needs a direct connection to the battery, why do you have such a strong opinion about running a ground for the amplifier to the battery? Let me cut to the chase. I'm a couple of months away from starting my 25th year as a full time professional 12v av installer. The last 13 of those years self employed. Right now my backlog is about 12mo. Unheard of in my industry, especially in this economy. Ive worked with just about every manufacturer and currently have very close relationships with jl audio, kenwood, pioneer. Not one of the top tech advisors for any of those companies would recommend or require a ground being run directly to the batt for that application. In fact, doing so can actually create other problems and could have a negative affect on overall performance. There are very few things I would speak forcefully about or claim to be an expert in on this forum, but this is one of them. Following the manufacturers guidelines is NOT a band aid, Its common sense.

 

[ntsqd]

My point was clearly missed. That is that the short ground recommendation is a band-aid covering up the lack of adequate noise filtering. Something that the ham radio mfg's are willing and able to do.

 

[bronconut73]

My point was clearly missed. That is that the short ground recommendation is a band-aid covering up the lack of adequate noise filtering. Something that the ham radio mfg's are willing and able to do.

You think expensive, high end amplifiers are not as filtered as a Ham Radio?

With harmonic distortion below.05% on the models below....

Macintosh,
JL,
Alpine,
Etc....

Do Ham radio's have that low of harmonic distortion?

 

[ntsqd]

On their power input, no I do not. HD is a rating of what the amp can do, not how well it filters the input power.

 

[bronconut73]

I am not at randbjorn's level but I worked in audio shops as a kid.

I have competed and won numerous audio competitions.
I have always installed my own equipment.

I can't help but think that we (me & randbjorn) are simply talking about other stuff than you nsqdt.
Because I know how crazy smart you are.....

I just think we are not comparing Apple's to Apple's.

 

[Dannyboy71]

I used 8 gauge with a mega fuse near the battery.
concerning your negative connections here is some interesting reading http://www.w8ji.com/negative_lead_to_battery.htm

 

[randbjorn]

I used 8 gauge with a mega fuse near the battery.
concerning your negative connections here is some interesting reading http://www.w8ji.com/negative_lead_to_battery.htm

I did not have the time/inclination to type that much info but that link is the long form of what I was trying to explain to ntsqd. Thanks dloskam!