SBD, grounding wires for aftermarket amps

[joe603]

So I have a request for SBD...or maybe a test scenario.

I have aftermarket stereo equipment installed in my G. The sub amp is pretty big, MTX 7801 superamp (900+RMS with 1,800 peak watts). If I have it turned up, the amp actually slows down the car when a big bass note hits! Most likely, the current draw from the amp is bogging down the alternator, which in turn slows down the belts...which is felt on the drivetrain. (like when the AC compressor kicks on...you see a drop in RPMs)

I'm wondering if the grounding on the car isn't all that it should be...

I do have 4-gauge ground wires on both the amp and the negative from the battery.

Would a wiring kit help with the charging system? Have you done a kit on a car with an aftermarket stereo system installed?

The system has a 1F CAP, Optima Yellow top and 4ga wiring, professionally installed.

[SVTCOBRA]

that's one clean battery compartment!

[Sentientbydesign]

My brain is too fried to deal with this. It MIGHT help. It SHOULD help. Will it? No clue.

Here's what I'll offer. Email me, I'll give you the Staff discount. If it makes difference, then you keep it.

If not, return it. You pay $14 total for shipping (back and forth).

I actually have a blue kit sitting on my desk that was made for someone here on NICO, but there was a discrepancy (sp) and he's has HR not the DE, so I'll need to make him another one. If you want it, I can have it in the mail by this afternoon and to you by Wednesday or Thursday.

[pfarmer]

So I have a request for SBD...or maybe a test scenario.

I have aftermarket stereo equipment installed in my G. The sub amp is pretty big, MTX 7801 superamp (900+RMS with 1,800 peak watts). If I have it turned up, the amp actually slows down the car when a big bass note hits! Most likely, the current draw from the amp is bogging down the alternator, which in turn slows down the belts...which is felt on the drivetrain. (like when the AC compressor kicks on...you see a drop in RPMs)

I'm wondering if the grounding on the car isn't all that it should be...

I do have 4-gauge ground wires on both the amp and the negative from the battery.

Would a wiring kit help with the charging system? Have you done a kit on a car with an aftermarket stereo system installed?

The system has a 1F CAP, Optima Yellow top and 4ga wiring, professionally installed.

I doubt very much that a grounding kit would help if you are outrunning your alternator. If your car is feeling the effects of the alternator the fix is to upgrade the alternator and then possibly separate your audio from the rest of the system (dual output alternator for example). If the alternator is physically sucking power from your car to the point you feel it then that condition should stay the same. A second battery at this point may help for peak use but overall your alternator still needs to rotate.

Now a different pulley may help but this depends on the rpm the car is normally driven at and the characteristics of the alternator.

But you may actually be dropping the voltage to the system to the point where it affects various modules. I would connect a meter to observe this.

Do you have a capacitor located at the amp?

Perry

[suby01]

go with 0 gauge wire. for power and ground.

also, how long is your ground wire from your amp to the car frame?

[Sentientbydesign]

Got some food...

Ok. Joe, we have to determine if the alternator is being maxed out OR if the wiring is limiting current.

I honestly can't tell you which is happening.

[kmckis1029]

i agree with perry... sounds like your alternator cant handle the power draw... im surprised you havent got stuck cause your car wouldnt start

seperate battery... bigger cap... smaller amp(i know you would hate that)... bigger grounding wires... higher output alternator... a combination of these will fix the problem

i would try bigger wires and a bigger cap first...

[suby01]

i agree with perry... sounds like your alternator cant handle the power draw... im surprised you havent got stuck cause your car wouldnt start

seperate battery... bigger cap... smaller amp(i know you would hate that)... bigger grounding wires... higher output alternator... a combination of these will fix the problem

i would try bigger wires and a bigger cap first...

+ shorter grounding wire.

[joe603]

I think it's the alternator...all other fixes have been done (short ground wire from Amp to car, new battery with upgraded 4ga NEG wire, and a 1F cap).

I was just wondering if you've had a customer who had similar problems that a grounding kit fixed.

[Sentientbydesign]

You could do some current measurements off of the alternator and see if that's the problem.

[tollboothwilley]

I have a similar setup. I run 0 gauge wire to the Sub amp with a 1F capacitor.

What I think you might want to try is to upgrade the Battery Neg -> chassis ground. Also upgrade the Alternator ground -> Battery Neg.

Those are the only wiring upgrades that could be beneficial, aside from rewiring the amp with 0 gauge.

[pfarmer]

I have a similar setup. I run 0 gauge wire to the Sub amp with a 1F capacitor.

What I think you might want to try is to upgrade the Battery Neg -> chassis ground. Also upgrade the Alternator ground -> Battery Neg.

Those are the only wiring upgrades that could be beneficial, aside from rewiring the amp with 0 gauge.

From what I see is that the battery ground has already been upgraded to 4 gauge which should be good for about 135 amps. But.......... if you are driving 900 watts rms. then the rule of thumb that is often used is to allow an additional 40% for actual amp loading. This gives about 1260 watts.

At 12 volts this would give you a draw of about 105 amps. #2 would give you about 181 amps. According to the FSMs you have a 110 amp alternator on a 2005. Previously when I looked into this the fuseable link for other models ran 140 amps which is typical for an alternator with a 30% fat in its rating. Keep in mind that one is not likely to be driving around at 5000 rpms all day, the max rating for the alternator. At a crusing rpm of about 2500 it isn't even 100 (keep in mind alternator speed).

Now consider that once the car is started you are basically running off of the alternator, not the battery. While the battery cables to the amp are in range this doesn't take care of the undersized alternator. Even with its fat you are potentially loading right on the upper limit during the high output transients. Increasing the battery cable size will not increase the capacity to the amp except when the car is not running, it will only mask the real issue on a very limitied time period with the car running. What needs to be done is to increase the alternator capacity keeping in mind that that it may be necessary to also upgrade its cabling as well since that is what is really supplying the car with its power. You can't get 200 gpm of water to your house with a 150 gpm pump regardless of the size of the pipes.

The separate battery will only help if your actual draw averages less than what the alternator can supply, it actually decreases to a certain extent your long term capacity.

One thing to check is to see if the amp is actually clipping during the transients. This isn't unusual and goes largely unnoticed especially for subs. The point here is that the amp is rated 900 watts rms. In the case of a sine wave this is most likely the rated power output. But if you are clipping then the actual output of the amp can increase substantially as you approach a square wave. Along with that comes an increase in the power it requires from the electrical system. This is something to look at as the fix then would be to turn down the inputs until clipping disappears. Still doesn't cure the 110 alternator.

Perry
Modified by pfarmer at 12:03 AM 9/2/2009