car electrical voltages/noise

Hi all, So I am having electrical issues with my install on a 2008 Mazda 6. My system was too powerful for the factory alternator and battery, so I am in the process of replacing them. I have already replaced the battery with a Kinetik HC1800 and am about to install a new HO alternator. Before installing the alternator, I did some voltage tests out of curiosity. For starters, my battery voltage is 13.1 with the car off. Isn't this a little high? Is that a problem? When the car is running, with AC on half, lights on, and low volume music (basically, factory alt should be able to handle it) the voltage across the terminals is 13.7 at best. This seems a little low, right? I suspect that my alternator may be failing as I have abused it for about 6 months now with a too-powerful system. Would this explain the low idle voltage? I also have a slight amount of alternator whine through my speakers. From what I can tell, all my grounds are fine (solid contact, short length of wire, Alpine HU so not RCA issue, RCA/power opposite sides of car). Is it possible a failing alternator could cause alternator whine through the speakers? Lastly, I have a bit of noise through the speakers only when the car is IN GEAR. ie. if it is in park, I have it on low volume, it is clean. As soon as i shift into reverse, I get some slight noise, shifting into neutral the noise disappears, and into drive it comes back. Could this be alternator too? In any case this is the more annoying noise because it is slightly louder than the alternator whine. So if anyone has any suggestions on what to check out on this one I would appreciate it. The system is an Alpine X305s HU, with the Alpine powerpack mini amp running the speakers. Have 2x 12" Kicker CVX subwoofers with a Kicker ZX 1500.1 amp running them. Power and ground on big amp is 0 gauge. Engine wiring has been upgraded to around 2 gauge (going to replace charge wire with 0 gauge when I replace it). The small amp and HU up front are grounded decently, at the exact same spot on a sort of crossbar connected to the chassis. Any help/thoughts/whatever appreciated! Thanks!

Very few stock alternators are going to put out 14.4 under load, especially a car alternator. 13.7 isn't really all that low when you said that is with lights, AC, and music on. What is your reading with all of those off?

Have you done your Big 3 Upgrade? That will help you find some "lost" voltage and it is essential if you think you'll be putting a new HO alternator in.

MECP Basic Installation Tech

Certification ID: CEA195600

Pioneer AVIC-X920BT

Polk Audio DXi 6500 - front

Rockford Fosgate Power T1693 - rear

Alpine MRP-F300

Alpine MRP-M500

Alpine SWR-1242D

As far as your battery voltage goes, 13v isn't going to hurt anything.MECP Basic Installation Tech

Certification ID: CEA195600

Pioneer AVIC-X920BT

Polk Audio DXi 6500 - front

Rockford Fosgate Power T1693 - rear

Alpine MRP-F300

Alpine MRP-M500

Alpine SWR-1242D

13.1V is ok for a battery. After battery charger removal, the battery retains "surface charge". A typical 12V lead-acid battery that is full at 12.6-12.8V often has up to ~13.8V due to surface charge. Surface charge should disappear overnight (or 24 hours) or can be removed with a load. FYI - some reckon 10-15 minutes on high-beam to remove surface charge. I mention that to annoy capacitor freaks that reckon batteries quickly drop to under 12,8V.) Yes - 13.7 is a bit low. (Assuming "normal" temperatures...) The norm is 13.8 to 14.4V. (Ideally starting at 14.4V then dropping to 13.8 when the battery is fully charged.) It might be the alternator's output profile - ie, needs above idle speed etc) It might be bad connections or undersized wiring - ie, voltage drops increase with current - have the Big-3 been done? (You must upgrade ground paths and alt-battery connection.) Hence what is the alternator voltage (heavy B+ output to its chassis) compared to across battery (+ve to -ve terminals) eg - 14.4V & 13.7V? If it is merely a low (voltage) output, that can be boosted easily assuming its regulator has external sensing (eg, not a "single wire" D+ type, but has the charge light output (D+ or L) and Ig or S (Sense) etc. [ Do I hear "How?"? Insert a diode with voltage drop 0.2V - 0.7V to increase output voltage by the same. A local dude is selling such a device for $42 on eBay - it's one (or two reversed) $0.05c 1N914 diodes in an ATS fuse body! ] But it could be a worn alternator... EG - blowing any of it 6 main power diodes reduces its output as well as introducing NOISE. (I stopped using older Bosch alternators because they'd blow their power diodes way too easily.)    Generally though, you can't "wear out" an alternator. They are self-limiting wrt output power (current). That doesn't mean their brushes last forever, nor that they avoid crap diodes & other poor or cheap design. And overheating has it effects. [ My first non-Bosch failure was after extreme abuse - but it was only an internal sensing diode that became un-soldered. ] Alas no straight answer. But hopefully enough to assist fault finding. (Assuming you have a voltmeter.) PS - thanks mrm1776. I started this reply over an hour ago. I hate phones!

Thanks for the info. I just got finished putting in the new alternator so the voltage is not an issue anymore. Unfortunately, both forms of my noise are still there. :( ie. the alternator/engine whine (varies with engine rpms) and the 'in-gear' noise. Some more info on the in-gear noise if anyone has ideas: Again, it only occurs when the car is in gear. It does not occur in neutral or park, but does in drive and reverse. However, it stops when the car hits 3rd gear! If I am playing a silent part of a track, you hear the noise as you accelerate through 1 and 2 gear, then when you hit third, it vanishes. When I stop and the car downshifts to 1 gear, it appears again. Any ideas? Will also take any suggestions on the alternator whine. I determined (i think?) that it's not the subwoofers by unhooking the RCAs going into the subwoofers and the whine was still there. I tried grounding the outer RCA shields a-la-pioneer style but that just made it worse. Thanks everyone.

Also this seems to have been lost in the first post: my engine wiring (ie. big 3) has been upgraded. The alternator charge wire is 0 gauge. The chassis and engine ground wires are something around 2 gauge (not quite as heavy/thick as the 0 gauge I used. If it has any bearing at all, the factory negative battery terminal, is still in the engine compartment, but is NOT hooked to the battery. So the wire from this terminal looks like this: O--------X-------------Y O is the factory terminal (where it used to connect to the negative battery terminal), X is the chassis ground, and Y is the engine ground. This is how the factory wiring was set up, and this is one continuous wire. Point X now also has the larger 2 gauge wire attached that then runs to the negative terminal of the battery.

So just to clarify, all original factory wiring is still in place. So the alternator has the factory and the 0 gauge wire attached, which take different routes but both end up at positive terminal. And the factory wire from point X to Y (chassis to engine, which in factory setup was negative terminal to chassis to engine) is also still there, as well as a connection of the 2 gauge wire that goes from negative terminal to engine ground. Sorry for all the blabbering just trying to give anyone with a clue all the info! Thanks!

My general rule is that ground cables should at least equal the power cables (gauge etc). The logic is that whilst +12V can come via various paths (alternator, battery, other batteries etc), the grounds alone might carry ALL that current. [In simple terms, if a load takes 100A from the battery & 100A from the alternator, that's 200A thru its ground (which could be all from battery or alternator....).] Also, grounds are the easiest resistance to reduce. EG - doubling the battery to chassis & chassis to alternator/engine (and load to chassis etc) HALVES those cable-path resistances. How much +12V cable is required to do the same? Plus if I have (say) 200A +12V cabling, I'd like 2 x 200A grounds to that if I lose one, I don't melt my electrics. (But how do you know you have lost only one...? Ah ha!) As to leaving all factory standard wiring there and ADDING the extra wiring, IMO as said elsewhere, that should simplify any warranty or insurance claims.... You have added a redundant ground path with the -ve terminal to engine. I often do that instead of duplicate -ve to chassis & chassis to engine. Excluding ground loop issues - and from a redundancy POV - it's the same thing, but cheaper and lighter. (TekHed me would call it 2n+1 redundancy versus two n+1 redundancies. Note that redundancy here means "spare backup" or "fail-over" paths etc - it does not mean wasted or useless. (Though like any back-up, it is usually total waste until required - just like a fire extinguisher.) The dangling factory -ve terminal shouldn't matter. A +ve might act as an antenna for noise, but that isn't an issue for this dangling ground. And if your dangling ground should short out one of your other -ve-chassis-engine grounds.. der, um, let's see - will that be a hazard... oh yes - your grounds could be too powerful and therefore melt your engine - you'd better get a bigger engine to protect against that! (Yes - I'm kidding. I'm using the same logic as a too big a battery or alternator blowing normal electrical components.) Gear noise - if it were manual and quiet only with clutch in or in its 1:1 gear (typically 4th in Jap & Euro cars), then I'd say it's your central main-shaft bearing.    But for electrical noise.... Modern auto boxes do (or can) use CPUs and electrical equipment so that could be the problem. Maybe check gearbox ground, or the gnd connection for any connection/cable to the gearbox. Older boxes might have had reverse light switches (manuals did, but auto's can be in the console, though Mazda used switches on the auto boxes themselves in the 1980s-1990s). Later they added to electric speedo senders. And electric overdrives. And electric thingos for whatever modern reasons.... As to you blabbering - sorry - I didn't notice. (LOL!) (Besides, extra info is better than under-info!)

I can't quite tell if you think the ground wiring being smaller than the charge wiring could be an issue or not. I'm thinking it is NOT the cause of either of my issues because prior to installing my new alternator (today) the wiring was identical for charge and ground, and the issues existed. So what I'm gathering is: You don't think my wiring setup in the engine is the issue, assuming that all connections are solid, but that I might check the ground on the gearbox. I will try to check this, though I don't really know what a gearbox is or why it has a ground haha, but I do have the manual. For the record, this is an automatic transmission. And thank you for your response!

Sorry - my bad. I think 2G is ok for what you have (I'd have to check - but others know better.... I design by resistance-length x current for (IMO) acceptable voltage drop.. Chilton's reckon a 7V drop is ok do they????!!!). I did mean more as a general comment - ie, ground "exceeds" power gauges. But if you need 4G and gnd is 2G and power is 0G, both are "over spec". (IE - better than ok.) And thanks - I figured the box was auto - I spotted the tell-tale park. Since a gearbox is firmly bolted to the engine, it is grounded. Or should be - I have seen apparently STRONG metal to metal bondage that has poor electrical transfer - ie, like engine to gbox with several hefty & tight bolts.    If it were to be "floating", then it could act as an antenna that radiates static etc from rotating gears. (Static causes popping when it arcs - that was a problem with wheel hubs in ye old days, and pre-bonded bonnet & boot lids (trunk etc) and doors.) Of if floating, it won't shield any interference (EMI/EMC) from internal coils etc. My 1986 auto has electrical components. Yours is 20 years newer and bound to have electrical gizmos. And geez man - everyone knows what a gearbox is - it is an extra thingy that costs extra money in a vehicle! I reckon it's only there as a stick-mount so people can sell better looking knobs, and of course for the rest of us to give money to those that can fix noises. Wiki no doubt has its technically biased view on what a gearbox is in case you desire alternate views - no matter how misleading they may be. (I'll review that part of problem later...)