If the power wire to the Amplifier is too small and is causing the Amplifier to draw more current due to dropping voltage and this is causing the headlights to drop then the correct place is near the amplifier. Putting it near the amplifier is similar to using a surge cushion in a plumbing system to prevent "water hammer. You will want to place the capacitor as near the amplifier as possible and you will want to increase the wire size to the maximum allowed by the amplifier to allow full use of the CAP. (You can check for this voltage drop with a VOM.)
If the wires are sufficiently large enough and the reason for the Lights Dimming is that the Alternator is too small then you COULD put the CAP under the hood but I have only heard of putting the CAP under the hood as a noise filter or due to size limitations in mounting it near the Amp. However if the reason for the CAP is because of the Amplifier then you need to place it by the Amplifier. The shorter path between the CAP and the Amplifier the better due to resistance in the wire robbing you of energy the cap is supplying. If you look at most high quality amplifiers they internally have pretty large capacitors.
Realize that in both of these cases the CAP is a band-aid and doesn't resolve the original issue. As long as you use them properly there is nothing wrong with using Capacitors but it is kind of like using Duct Tape to extend the life of a hose when you really should replace the hose. The fix for the first item is larger wires and the fix for the second is a new, larger alternator or multiple alternators. In some cases where caps are used to get rid of noise the noise is generally due to high performance parts "leaking" RF into the power system and the CAP will filter it out. But one should realize that CAP companies are in place to make money off selling you capacitors...
If you DO use a CAP I would NOT put it under the hood for this purpose. The reason why is if the problem is undersized wires you will still have undersized wires. Why are undersized wires a problem? Think of it as a pipe with water running through it. If you try to put more water through a pipe the velocity increases. The pressure against the pipe then increases as well until it reaches a point it explodes. A wire is very similar except the resistance of the wire increases as the length gets longer so as you go longer you need larger wires. Which means for the most part that as your wire gets longer it will act as a smaller wire. If you use too small of a wire for your amplifier it drops the voltage allowed through it. Anyone that knows electricity can tell you that if you require 1200W at the amplifier and normally use 100AMP to get there at 12V if you drop this voltage to 10V you will require 120AMP through the wire. Why is this a problem? If you were using a wire rated for 100AMPS you are now 20 amps over the rating for it and this wire will heat up and eventually the copper will slowly burn off and you will end up with things like melted connectors or potentially a burned wire. As the copper burns the resistance increases and you could end up with an electrical wire fire. So like I said, putting the CAP under the hood is the WRONG place because it will hide this wire issue until you have a fire in your car or you blow fuses because the amperage is too high.
My OLD 2001 Mitsubishi Eclipse GT:
"The Project That Never Ended, until it did"
next project? subaru brz
If the aim is to stop lights dimming, then the cap should be at and for the lights.
If it's to prevent amp dips, then the amp - noting of course that a cap won't handle long burps etc.
In both cases, a battery will hold far more reserve power (voltage) than a cap.
The cap near the lights means that temporary amp and alternator dips are buffered by the cap and the cable resistance from the alternator/battery to the cap.
And with lights typically drawing far less than an amp, the cap will keep the lights higher for much longer than if it were at the amp.
But as I often ask, what is the aim of the cap? What dip do you want to overcome? If an amp dip is not audible, why bother at the amp?
Note too that undersized wires only increase the cap's (or 2nd battery's) effectiveness. It's the wires from the cap (or battery) to the target (amp or lights) that needs to be heavy (for surge/dip purposes).
And if amps are constant power devices as they should be and as suggested (ie, 100A @ 12V or 120A @ 10V), then voltage drops won't have an effect unless they drop below the amp's minimum voltage (or conversely, exceed the amp's max input Amperage capability). However few amps seem to exhibit this behaviour based on (1) the apparent effect of input voltage dips, and (2) ratings of many amps that show their output power increases with input voltage (ie, usually proportional to voltage-squared if it's a resistive load, or proportional to voltage if it is current limited).
I'll skip the issues of internal amp surge drops, and the separation of an amp's SMPS (PSU) from the amp itself which would allow a DC supply voltage to the amp of up to 120VDC (depending on local HVDC limits) - though this morning I replied about the latter on the12volt.com in response to HV amps (48VDC and higher). But 120VDC would mean up to 1/10th the copper requirements of 12V amps. (And wipes out the lucrative market that survives on the stupidity of LV amps and low-Ohmage outputs.)
For what is running now, I don't know precisely. It's the stock bose system that came with my truck and I added a mono amp/2 10s under the backseat. The bose setup has front and rear door speakers, tweeters above the dash, and a small sub under the center console.
They say ignorance is bliss..
Far from it in this case.
I had a moment of clarity and THINK I found the low audio issue. I did not understand the difference between line level/high level inputs and rca inputs. It was a non-issue when I originally ordered the wiring harness, but after the RMA I received one that is line level inputs only (the old one was RCA only).
Me being quick to solder I just put some RCA ends on the wiring harness and then plugged the pc's audio into those.
I'm going to call and confirm this with tech support friday. Hopefully there is a solution to use this harness as another rma would hurt my brain cells.
Well I'm going to give this thread a bump since the dimming headlights was not corrected as I had believed.
It is better but not 100%--in fact a headlight just blew out when I turned the bass to max and got out the truck to verify if they were dimming or not...
I upgraded the "big 3" to 1/0 awg yet the headlights still dim when the base hits. Does this mean it is time for a better alternator?
Specifically I ran
1/0 from alternator to battery1.
2/0 from battery1 to battery2.
1/0 ground from battery 1 to engine block.
1/0 ground from battery 2 to engine block.
1/0 ground from engine block to firewall.
Anything I may have missed that could help?
Blowing the headlight suggests an over-voltage, not a dip.
IMO the only way "short circuits" or bad connections causes bulbs to blow of from the repeated thermal cycling when of intermittent nature (short and repetitive).
The overvoltage could be due to your battery grounding to the engine depending on the type of alternator.
Usually the vehicle body/chassis is the "main" ground as that's what most electricals use. The battery(s) -ve and engine are then each strongly bonded to the body/chassis.
A drift between body and engine ground can cause an overvoltage from the alternator.
It could also be a faulty alternator (regulator) that overshoots its target voltage (~14.2V) though I'd consider that unlikely. I'd reroute your battery grounds to the body/chassis first, and preferably the same SOLID point as the engine ground (is the firewall solid enough; why not the chassis rail etc?). If the 2nd battery is remote, then a solid chassis/body GND should be fine.
Extra (redundant) engine to body GNDs won't hurt, and will protect from damage if the other(s) fails.
(I'll be unavailable for a few days.)
Great information as always.
Perhaps the blown headlight was unrelated as I monitored to voltage on the dash and never saw any spikes above 14.2, but it did dip down to ~13.9-14 when the bass hit.
I will try your suggestion of sending grounds direct from each battery to the chassis and see if that helps. However, the ground I ran from battery 1 and engine block-firewall follow the gm ground so I doubt their is an issue with grounding to the engine block from the battery--but I can always troubleshoot as I ordered enough 1/0 to make both connections.
When connecting to the chassis rail is there a typical spot gm would use to ground or should I just drill a new hole? (or is it sufficient to be lazy and run a self tapper?)
3 midterms next week so I probably should defer making any changes until next thurs-friday.
I just couldn't let this go.
So I made a 1/0 to go from battery 2 to chassis. Not fixed.
Made a 1/0 to go from battery 1 to chassis. Not fixed.
Then when I was ready to throw in the towel I went to check the alternator 1/0 connection at battery 1 and found that it was secure but the damn terminal screw was only tightened lightly by hand.
1.5 turn with a wrench and problem solved.
I think it's safe to say the headlight WAS related!
"Did you check if it's plugged in?"
Last edited by mrwesth; 02-15-2013 at 09:58 PM.
A self tapper for a main chassis/body ground? No! Whilst maybe ok for some loads, as a main GND they can not be relied upon.
My heavy grounds are usually 8mm bolts into captive (welded) chassis or body nuts, and that's for mere tens of Amps loads.
I use a 12mm or 14mm bolt into the engine block for the GNDs to chassis and battery.
I don't know what's available on GMs, but surely they'd have a good point somewhere. I have used engine mount points (chassis side) and cross-member bolts etc. I'd consider using suspension points - eg, swaybar body brackets.
I strongly disagree with some of the things Oldspark says at times and I don't think him and I will ever come to agreement on some items. But as far as this stuff is concerned.. I said it before.. You can never have too big of a wire...
As he said, NEVER use self tappers as a ground point... you ALWAYS want to use a bolt to make a solid connection. You also want to make sure you use a star washer between the car body and the connector you attach to your wire. This washer will bite into both the connector and the car body to make the best connection. No paint on the car body where you attach it. (You can always paint over the whole piece when your done if you are worried about corrosion but make sure the original connection is solid first.)
When looking for grounding locations and you are not running the wire all the way to the battery you will want to connect to the frame wherever possible.
If you are hooking to the sheet metal of your car you will want to ensure that the sheet metal has a solid connection to the frame (Or subframe in a unibody car.) The issue is if the sheet metal you are using as a ground only has limited connections and is spot welded in places then you do not have a good ground path and can have different ground potentials. Differing ground potentials is very bad because that means you have the possibility of different voltages being seen in your system. In the best cases this can be seen as noise, hum or other annoyances. Worst cases can be equipment failure or possibly fires when things are not properly fused.