# What powers an amp - the battery or the alternator?



## FastKat (Feb 5, 2017)

Who cares? Well I have two convenient places to tap power for my amps: A) on the battery side of a fuse, and B) on the alternator side of the same fuse. See 1,000 word pic below. A and B represent the places I can get power. The fuse is factory installed and integrated into the fuse block.

I know that car batteries run at about 12 volts and alternators run around 14 volts. I believe that amplifiers like more volts and therefore the alternator runs the amplifier unless the alternator voltage drops to 12 volts which should not be happening.

I am looking at running a 4 channel A/B amp and a 300 watt mono D sub amp.

Where do I tap power (location A or B) and more importantly why?


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## kyheng (Jan 31, 2007)

Just tap the power cable from battery to amp and call it the day. Don't make simple things complicated.


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## FastKat (Feb 5, 2017)

What you're saying is extremely complicated... maybe impossible... to do cleanly on my car. It would be a hack job. The factory battery cable assembly does not play well with other power cables!



kyheng said:


> Just tap the power cable from battery to amp and call it the day. Don't make simple things complicated.


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## nhtunes (Jul 31, 2016)

Its the same circuit so the same voltage, but hook in on the battery side of the fuse. The fuse is to shut down the alternator feed to the electrical system if there is a failure.


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## SPLEclipse (Aug 17, 2012)

Voltage is technically the same at all points in the circuit, so tapping at the battery or alternator will make no difference in the voltage the amp sees.

However you should consider that during dynamic peaks in the music your current draw will exceed what the alternator can provide. The battery is capable of several hundred amps of current, and if you draw that power from the battery and through the stock wiring back to the alternator and off to the amps, you might overload that factory cable and potentially blow the stock fuse. This would be really bad as you'd prevent the alternator from charging the battery at all and after 10-30 minutes you'd be stranded with no way to get the car home. If the fuse and wire gauge between the alt and battery is sufficient to handle the maximum current draw of the amps you are technically fine, but i'd prefer to not have any risk of blowing that fuse.

There are aftermarket battery terminals that feature a standard sized battery post-like connection. This lets you clamp you factory terminal down to the aftermarket terminal just like you would connect the factory terminal to the battery. That might help if you have a stock terminal with a lot of connections or it is otherwise difficult to disturb the factory terminal for another line. Knu makes one: http://www.knukonceptz.com/mobile-audio/battery-terminals/sp/ultimate-positive-battery-terminal/

You didn't mention it but i should say that you should make sure you fuse the added 12v+ line from the battery appropriately for whatever gauge wiring you use. You might know that already but I just want to make sure I put that out there.


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## FastKat (Feb 5, 2017)

You make a good point - that fuse size is likely based on the output of the alternator (or based on the size of the alternator wire which is based on the output of the alternator) so I am thinking that the alternator is not capable of blowing that fuse based regardless of whether it's powering amps. If the alternator was at max load and the amp wire started pulling additional load from the battery through that fuse it could be a problem.

This scenario during dynamic loads where the system voltage drops below the 14v output of the alternator to the 12v output of the battery - are the headlights dimming at that time? I would think yes.

That block looks pretty handy. If there was one that had the battery cable post on the top it could potentially work for me. The one in the link would turn my OE battery cable assembly 90 degrees and I don't think that world work... or if it did it would be a stretch.. literally! Pic attached.


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## thornygravy (May 28, 2016)

If you want a cut and dry answer to your question.. The battery when the engine isn't running, *ideally* the alternator when the engine is running.


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## High Resolution Audio (Sep 12, 2014)

SPLEclipse said:


> Voltage is technically the same at all points in the circuit, so tapping at the battery or alternator will make no difference in the voltage the amp sees.
> 
> However you should consider that during dynamic peaks in the music your current draw will exceed what the alternator can provide. The battery is capable of several hundred amps of current, and if you draw that power from the battery and through the stock wiring back to the alternator and off to the amps, you might overload that factory cable and potentially blow the stock fuse. This would be really bad as you'd prevent the alternator from charging the battery at all and after 10-30 minutes you'd be stranded with no way to get the car home. If the fuse and wire gauge between the alt and battery is sufficient to handle the maximum current draw of the amps you are technically fine, but i'd prefer to not have any risk of blowing that fuse.
> 
> ...


The first line of information in your post is false. Voltage is technically not the same in a circuit. In both AC and DC system there is a term called Voltage Drop. It is caused by the resistance or impedance in a cable. Voltage drop becomes especially important in a 12 Volt DC system because the voltage is so low, to begin with. 

As one sends 12 Volt DC current through a cable the voltage will keep dropping as the run of wire gets longer and longer. Eventually you would get a reading of zero. That is why it is imperative to use large cables such as 1/O or 2/O for feeders from the front of the vehicle to the rear to compensate for the resistance in the cable. 

If one just ran the size wire needed to supply the amplifier according to theory ( current alone), without taking into account voltage drop, then the voltage would be dramatically different at the end of a typical run from the front to back of a vehicle.


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## Holmz (Jul 12, 2017)

FastKat said:


> ...
> I know that car batteries run at about 12 volts and alternators run around 14 volts.
> ...


The 12V battery will be lower than 12V when dead, and up at 14+V when getting charged.

The alternator, via voltage regulator, controls the voltage of cars electrical system which is the same voltage everywhere on the power lines with the nuance of some small losses due to resistance and current.




SPLEclipse said:


> Voltage is technically the same at all points in the circuit, so tapping at the battery or alternator will make no difference in the voltage the amp sees.
> ...


^Correct^


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## gijoe (Mar 25, 2008)

High Resolution Audio said:


> The first line of information in your post is false. Voltage is technically not the same in a circuit. In both AC and DC system there is a term called Voltage Drop. It is caused by the resistance or impedance in a cable. Voltage drop becomes especially important in a 12 Volt DC system because the voltage is so low, to begin with.
> 
> As one sends 12 Volt DC current through a cable the voltage will keep dropping as the run of wire gets longer and longer. Eventually you would get a reading of zero. That is why it is imperative to use large cables such as 1/O or 2/O for feeders from the front of the vehicle to the rear to compensate for the resistance in the cable.
> 
> If one just ran the size wire needed to supply the amplifier according to theory ( current alone), without taking into account voltage drop, then the voltage would be dramatically different at the end of a typical run from the front to back of a vehicle.


Hopefully what he meant was that the voltage is the same on either size of the fuse. Besides the negligible resistance that the fuse causes, the voltage will be the same. 

Since we're on the topic. Voltage drops across resistors (technically anything that causes resistance) in a series circuit, but current remains the same throughout. Current drops in a parallel circuit, but the voltage remains the same.


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## Onyx1136 (Mar 15, 2009)

FastKat said:


> What you're saying is extremely complicated... maybe impossible... to do cleanly on my car. It would be a hack job. The factory battery cable assembly does not play well with other power cables!


What vehicle do you have that makes it so impossible to do simple things correctly?


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## kyheng (Jan 31, 2007)

FastKat said:


> What you're saying is extremely complicated... maybe impossible... to do cleanly on my car. It would be a hack job. The factory battery cable assembly does not play well with other power cables!


In this world, you can find many types of battery terminals. I'm not asking you to tap from the existing wiring which sure will be impossible unless you want to torch your car.
You can tap a power cable from alternator but remember, the alternator will be mainly used for powering your car's essential appliance and not car audio.


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## sirbOOm (Jan 24, 2013)

There is A LOT of misinformation in here.

Everything electrical in a car is technically powered by the alternator. When the car is off or the alternator is not engaged (in most modern cars, the alternator only charges when needed to maintain battery voltage), everything electrical is supplied power from the battery (which is a power storage device, a reserve), but only for so long as the reserve can manage to do so. Fundamentally, still, that power came from the alternator which is effectively a power generator. The battery is a power reserve that smooths the power output of the alternator (eliminating noise, calming voltage spikes should they exist, and compensating for the alternator's inability to react to sudden power needs, or dips).

There is a very important reason why there is one (typically) heavy gauge wire coming from the alternator to the battery. There may be a smaller wire that is for voltage sensing, but that's not important here. It is because all electrical items in a car should be powered after the battery for the aforementioned reasons AND after the fuse that exists between the alternator and battery, which is intended to prevent a serious problem should the single wire I mentioned short or the alternator spit out a sudden spike (malfunction) or potentially if you have a number of other electrical issues.

Do NOT attach your amplifier's power wire to anything but a point after the alternator to battery fuse and directly to the + terminal of a battery. 

There is always a way to connect your power wire directly to the positive terminal of the battery before any and all other fuses that exist already and are intended ONLY for the vehicle's existing electronics.

You may need to cut factory power wiring, get a different type of battery that physically fits and meets your car's minimum power requirements, or by some other means.

It would be helpful knowing what car this is and having a photo of the battery that is influencing this question.

And, yes, the alternator ALSO powers your car audio. Where on earth do you think the power comes from?


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## sirbOOm (Jan 24, 2013)

FastKat said:


> You make a good point - that fuse size is likely based on the output of the alternator (or based on the size of the alternator wire which is based on the output of the alternator) so I am thinking that the alternator is not capable of blowing that fuse based regardless of whether it's powering amps. If the alternator was at max load and the amp wire started pulling additional load from the battery through that fuse it could be a problem.
> 
> This scenario during dynamic loads where the system voltage drops below the 14v output of the alternator to the 12v output of the battery - are the headlights dimming at that time? I would think yes.
> 
> That block looks pretty handy. If there was one that had the battery cable post on the top it could potentially work for me. The one in the link would turn my OE battery cable assembly 90 degrees and I don't think that world work... or if it did it would be a stretch.. literally! Pic attached.


You can find my build log for my 2014 Silverado and in there are the parts I used to deal with a battery like this. I can't remember the details right now.


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## SPLEclipse (Aug 17, 2012)

High Resolution Audio said:


> The first line of information in your post is false. Voltage is technically not the same in a circuit. In both AC and DC system there is a term called Voltage Drop. It is caused by the resistance or impedance in a cable. Voltage drop becomes especially important in a 12 Volt DC system because the voltage is so low, to begin with.
> 
> As one sends 12 Volt DC current through a cable the voltage will keep dropping as the run of wire gets longer and longer. Eventually you would get a reading of zero. That is why it is imperative to use large cables such as 1/O or 2/O for feeders from the front of the vehicle to the rear to compensate for the resistance in the cable.
> 
> If one just ran the size wire needed to supply the amplifier according to theory ( current alone), without taking into account voltage drop, then the voltage would be dramatically different at the end of a typical run from the front to back of a vehicle.


I am very aware of voltage drop. It is such a non-issue in this instance that it would be pedantic and potentially confusing to the OP to bring it up. I guess i should have said "theoretically" or "assumed to be" or "on paper" instead of "technically".


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## FastKat (Feb 5, 2017)

Thanks for the replies and many different viewpoints.

My car is a 2013 VW Jetta. Pic of battery cable attached. I am not interested in getting a different battery or replacing that cable assembly. I will work around it the best I can. I could potentially put a large fork terninal on the clamp's screw but I would rather use a ring terminal (my original plan) though that nut is captive and cannot be taken off.

For those saying the battery plays a significant role in running an amp, I have 2 questions:

1) Do the headlights dim when the alternator is unable to supply the necessary voltage to the amp and the battery must step in?

2) What would happen if I started the car, unplugged the battery, and ran my amps hard? Sounds like an interesting experiment.


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## gijoe (Mar 25, 2008)

FastKat said:


> Thanks for the replies and many different viewpoints.
> 
> My car is a 2013 VW Jetta. Pic of battery cable attached. I am not interested in getting a different battery or replacing that cable assembly. I will work around it the best I can. I could potentially put a large fork terninal on the clamp's screw but I would rather use a ring terminal (my original plan) though that nut is captive and cannot be taken off.
> 
> ...


Instead of messing with the battery, run the power from one of the blanks in the fuse box. You're fuse box might be a bit different, but I'm betting you have a place to tap into. 

These lugs will fit (8awg). https://www.amazon.com/gp/product/B0747NHYZX/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1


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## FastKat (Feb 5, 2017)

We are on the same page. My fuse box / power distro center looks a little different. I got one of these bad boys to jump off the leftmost red wire (primary from battery) and then have the wire fall down through one of the blank channels. The other choice was the black wire from the alternator.

https://www.digikey.com/product-det...WOFhNQllKNkRGd1d1RWkwK1wvc1VjOGtUbTdtaHMifQ==



gijoe said:


> Instead of messing with the battery, run the power from one of the blanks in the fuse box.
> 
> These lugs will fit (8awg). https://www.amazon.com/gp/product/B0747NHYZX/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1


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## gijoe (Mar 25, 2008)

That fuse box is more different than I expected, but it still looks easier to get your power from there than directly from the battery. I like that lug though, as long as tapping into the black wire is safe that looks like an elegant solution. It's difficult to see, but do you have a blank spot next to the red wire?


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## Grinder (Dec 18, 2016)

FastKat said:


> 1) Do the headlights dim when the alternator is unable to supply the necessary voltage to the amp and the battery must step in?
> 
> 2) What would happen if I started the car, unplugged the battery, and ran my amps hard? Sounds like an interesting experiment.


Check this out: http://www.diymobileaudio.com/forum...cussion/116055-list-useful-diyma-threads.html


1) Read this thread: http://www.diymobileaudio.com/forum...134202-big-3-caps-general-electric-stuff.html

2) Let all the smoke out? I wouldn't try it.


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## FastKat (Feb 5, 2017)

Yea, there is a blank spot there but there is no metal bus bar at that slot... it is all plastic. The black wire is from the alternator and feeds back to the battery through the box bus bar. It is fused at the bus bar.

That terminal was a nifty find. Can't wait to install it! Is that pic from your car? A VW?



gijoe said:


> That fuse box is more different than I expected, but it still looks easier to get your power from there than directly from the battery. I like that lug though, as long as tapping into the black wire is safe that looks like an elegant solution. It's difficult to see, but do you have a blank spot next to the red wire?


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## FastKat (Feb 5, 2017)

Meh, I doubt it. Certainly not on a brief testing basis. 



Grinder said:


> 2) Let all the smoke out?


You can take just about any newish car, start it, disconnect the battery, and drive it from NYC to LA with all the lights on, fans on full blast, defrosters on, etc., and be fine. I understand that a sound system can be demanding though I'm not sure if it is practically different than the above.


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## Grinder (Dec 18, 2016)

FastKat said:


> Meh, I doubt it. Certainly not on a brief testing basis.
> 
> 
> 
> You can take just about any newish car, start it, disconnect the battery, and drive it from NYC to LA with all the lights on, fans on full blast, defrosters on, etc., and be fine. I understand that a sound system can be demanding though I'm not sure if it is practically different than the above.


If you already know the answer, I can't imagine what would be so interesting to you about such an experiment, and why you would bother to ask the question.


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## FastKat (Feb 5, 2017)

The question was to get people to talk about the transition between alternator voltage and battery voltage and what that looks like from a voltage and current standpoint WRT it's effect on the devices on the electrical system (lights, etc.) I think discussing that will help me [us] understand whether or not (or when) the battery plays a role in a properly running charging system powering an appropriately sized sound system.

My goal is to have mu alternator support my relatively modest amplifier requirements without having to draw from the battery. I look at drawing from the battery as a failure of the alternator to do its job.



Grinder said:


> If you already know the answer, I can't imagine what would be so interesting to you about such an experiment, and why you would bother to ask the question.


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## Holmz (Jul 12, 2017)

FastKat said:


> ?..
> 
> My goal is to have mu alternator support my relatively modest amplifier requirements without having to draw from the battery. I look at drawing from the battery as a failure of the alternator to do its job.


The battery always acts as a capacitor to both smooth out ripple, and it provide energy... especially when the alternator needs to supply power and it take some milliseconds to respond.

There is no failure. It is working as designed, and they usually work.


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## Grinder (Dec 18, 2016)

FastKat said:


> ...My goal is to have mu alternator support my relatively modest amplifier requirements without having to draw from the battery. I look at drawing from the battery as a failure of the alternator to do its job.


It's not necessarily because your alternator isn’t powerful enough to run all your gear. Presuming you have an adequately sized alternator, at any given moment (even while running your amps “hard,” presuming you’re not listening to test tones or the like) your alternator is unlikely to be running at or near its capacity, even though your headlights might be dimming to the beat; because:



SPLEclipse said:


> ... during dynamic peaks in the music your current draw will exceed what the alternator can provide...


…at any given moment. 





An alternator is not designed or equipped to instantly respond to every load, particularly very large and instantaneous loads. This is where a battery (and The Big Three) comes into play:



sirbOOm said:


> ...The battery is a power reserve that smooths the power output of the alternator (eliminating noise, calming voltage spikes should they exist, and compensating for the alternator's inability to react to sudden power needs, or dips)...


This is why it is unrealistic to expect one’s battery to, under no circumstances (no matter how brief, and how exceedingly little it actually matters) fulfill a load while the car is running. Indeed, such loads are (apart from starting the car, and several other reasons ^^^), exactly what the battery is there for.





And while it might be true that:


FastKat said:


> ...You can take just about any newish car, start it, disconnect the battery, and drive it from NYC to LA with all the lights on, fans on full blast, defrosters on, etc., and be fine...


...There is essentially nothing especially instantaneous (or even particularly large) about any of those loads; and all is well, as long as those loads (and potentially much more) do not exceed the capacity of the alternator (and all wiring and thermal/overcurrent devices).





For all these reasons, and given my level of knowledge (and yours), it is not so easy to predict what might happen if you: 


FastKat said:


> ...started the car, unplugged the battery, and ran (your) amps hard….


...Which is why I replied with:


Grinder said:


> Let all the smoke out? I wouldn't try it.


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## FastKat (Feb 5, 2017)

Partly agree, partly disagree.

I have a 140 amp alternator. If my amps, under normal and even louder music listening levels, are pulling up to 40 amps, am I really overdrawing the alternator?

Still unanswered... if your alternator can't supply the demanded power and the amps pull power from the battery, is voltage dropping across the entire electrical system and then causing your lights to dim? I think yes. That means everyone that has amps pulling power from their batteries has dimming headlights.


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## FastKat (Feb 5, 2017)

Aren't their actual capacitors in the amp power supply for this exact purpose?



Holmz said:


> The battery always acts as a capacitor to both smooth out ripple, and it provide energy... especially when the alternator needs to supply power and it take some milliseconds to respond.
> 
> There is no failure. It is working as designed, and they usually work.


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## Holmz (Jul 12, 2017)

FastKat said:


> Aren't their actual capacitors in the amp power supply for this exact purpose?


True - they supply it to the amp... but the 140A alternator may be putting out 15A, and then you turn the spotlights on at dusk. and the load goes to 50A.

In the 0-1/4 second the that the alternator goes from 15 to 50A the battery may be used.


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## Grinder (Dec 18, 2016)

FastKat said:


> Partly agree, partly disagree.


That's cute. 






FastKat said:


> I have a 140 amp alternator. If my amps, under normal and even louder music listening levels, are pulling up to 40 amps, am I really overdrawing the alternator?
> 
> Still unanswered... if your alternator can't supply the demanded power and the amps pull power from the battery, is voltage dropping across the entire electrical system and then causing your lights to dim? I think yes. That means everyone that has amps pulling power from their batteries has dimming headlights.


You obviously still don't get it.


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## 04quadcab (Dec 31, 2017)

A lot of interesting discussion about alternator and battery power. The practical issues here are 1) Where to tap in and 2) Where to put the fuse?

The short answer is 1) At the battery and 2) as close to the battery as possible. The original poster is having trouble accessing the battery positive, and it seems that the solution is to tap into the factory fuse distribution box. I am not familiar with this particular car, so I would to see some more pics of the problem and the solution.


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## FastKat (Feb 5, 2017)

If you were sitting here next to me I'd be happy to discuss any element of your response (I think this stuff is fun!) but in this online environment I didn't think writing a detailed respone would have lead to fruitful discussion.



Grinder said:


> That's cute.
> 
> 
> 
> ...


What I don't get is how everyone's 12v batteries are supplementing the amps on their 14v charging systems without their headlights dimming while acknowledging that voltage is constant across the electrical system less voltage drop from line loss. The answer looks pretty simple to me: either their amps don't need the battery power (alternator power is sufficient) or their voltage is in fact dropping causing lights to dim, flicker, etc.

This is not my first wiring project. Pic below of one of my most fun... making an LS1 swap + GM trans wiring harness from 5 different vehicle OE harnesses and a stack of wiring diagrams that went into an old Jag. It worked the first time! Still, I don't know everything and have been wrong before, that's for sure...


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## Holmz (Jul 12, 2017)

FastKat said:


> ...
> 
> What I don't get is how everyone's 12v batteries are supplementing the amps on their 14v charging systems without their headlights dimming while acknowledging that voltage is constant across the electrical system less voltage drop from line loss. The answer looks pretty simple to me: either their amps don't need the battery power (alternator power is sufficient) or their voltage is in fact dropping causing lights to dim, flicker, etc.
> ...


The battery is charging when the voltage is higher than 12V, so it is as you suggest above.

If you had those multi kW amps, that were also not regulated then they would possibly pulling down the system so that the battery has to keep the voltage from dropping.

If the lights were flickering, then you would know that the alternator is not keeping up at least some of the time.

So put the amp cables behind a fuse as was suggested earlier, and be happy.


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## Grinder (Dec 18, 2016)

FastKat said:


> If you were sitting here next to me I'd be happy to discuss any element of your response (I think this stuff is fun!)


What is fun? Arguing how many angels can dance on the head of a pin? 






FastKat said:


> ...but in this online environment I didn't think writing a detailed respone would have lead to fruitful discussion[/B].


Why not? 

By any objective measure, you have received a number of sincere and sufficiently detailed responses to deal with the subject at hand. If that's not contributing to fruitful discussion, I don't know what is...

With all due respect, the least you could do is drop the dismissive attitude, and perhaps take the time to respond in-kind. After all, we're only trying to help. 







FastKat said:


> What I don't get is how everyone's 12v batteries are supplementing the amps on their 14v charging systems without their headlights dimming while acknowledging that voltage is constant across the electrical system less voltage drop from line loss.


First of all, as you seem to draw a distinction between a "12 volt battery" and a "14 volt charging system," it might bear mentioning that a 12v automotive battery whose resting voltage (i.e. no load or supply for several hours) is 12.0, is for all intents and purposes at 0% SOC (dead); while an automotive 12v battery whose resting voltage is 12.8, is at 100% SOC (fully charged).

While the car is running, and the battery is at reasonable SOC, the entire system, battery included, is at ~14 volts; and with ordinary accessory loads, voltage throughout the system is essentially the same.



In any case, if it weren’t for voltage drop (somewhere, no matter how brief), your headlights would not be dimming.

Given reasonably sufficient ampacity of your car’s wiring system (including that of your audio gear, of course), if you were to measure the voltage at any location, you would see essentially the same sort of voltage drop as that which is indicated by the dimming of your headlights.


Whether this is a problem or not (and/or how one might solve it) is another matter.







FastKat said:


> The answer looks pretty simple to me: either their amps don't need the battery power (alternator power is sufficient) or their voltage is in fact dropping causing lights to dim, flicker, etc.


I know you don’t like to hear it, but amps played hard (certainly to the point of dimming lights) really do need both the battery and alternator while the car is running (for reasons that seem to have been made abundantly clear by myself and a number of our fellow members).

If you disconnect the battery and crank the tunes - lights, fans, defrosters, etc. notwithstanding - at the very least, voltage drop will be much worse than with the battery connected.






FastKat said:


> This is not my first wiring project. Pic below of one of my most fun... making an LS1 swap + GM trans wiring harness from 5 different vehicle OE harnesses and a stack of wiring diagrams that went into an old Jag. It worked the first time! Still, I don't know everything and have been wrong before, that's for sure...


That’s awesome!


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## FlyingEagle (Sep 22, 2017)

The last page of responses, along with a multitude of earlier responses in kind, have summed up the issue with large current draw in short bursts or longer, as it relates to the vehicles electrical system and its ability to handle the extreme draw that it was not designed to. Yes, it can handle up to a certain current level (or at least to the level of a hot saturated alternator/rectifier bridge/regulator assembly) whether controlled singularly internal to the alternator or external by a device or ECU. If you expect more, you need to design or reconfigure elements in the system. Great ideas about using a newer style of headlamp bulb and related control mechanism that is less prone to dimming as voltage varies, gets you a bandaid but will work just fine.

I don't see much more point to the thread if there isn't much more agreement on the OP's end, as taken from my point of view. I have seen a lot of great and truthful information posted here, and none of it is meant to demean the OP. I will backup my initial statement and only post thus far in the thread, with the fact that I am a licensed automotive service technician and work with these systems on a regular basis. It is actually kind of nice to sit here and see so many people from other walks of life, who are able to live and breathe well beyond the daily experience of those deep in the repair business.

Oh, for anyone reading about disconnecting a battery connection while the engine is reading = DON'T just DO NOT. 

It is the best way to spike voltage in the charging system, and can and has done serious damage to many vehicles electrical systems. Even a loose battery post will do the same thing if you are lucky enough to get high enough amperage through to start the car and then keep it operating ....

One thing that comes to mind as it relates back to charging systems is the relation of the alternator design. Some give pitiful output at idle and require much better RPM to be stable and provide decent and higher current output, while others are better at idle and kind of "top-out" or are designed not to be in a super high RPM environment. They do make clutch overrun models now too. I watch my voltage swing as my turn signals operate on my 1989 Mitsu powered vehicle. It is the design of my alternator assembly and ECU control, but mainly the alternator that is at fault. I can install LED's in place and it will likely be a much better affair. I have installed larger gauge wiring ala Jaguar XJS (0/2) through the vehicle and run a battery in the trunk with no volt drop across the circuit - this voltage issue with signals and other elements are symptoms of a design that is insufficient to meet high demand/load. The only cure for most and a better and more stable idle voltage (even with fans and other loads coming on) that goes along with it, has been to install a GM Saturn alternator assembly that oddly enough has super stable voltage at idle and can provide more current, with the added bonus of having nearly identical wiring at the plug too.
The only way to get a better setup was the replace the part that was barely able to keep up with the factory loads as it was. For reference it didn't matter whether the alternator was a 65A or 90A unit (which I use), it was the design. They provide low current at low RPM and I am sure the start point for charging is barely lit at the point of idle, and my lightened flywheel doesn't help to keep this process inline either. Did I mention that the more heat you added to the equation ... the worse the effect became! Missing exhaust heat wrap scenarios and more are what kill the regulator/rectifier. There isn't much more you can add to this situation, as design will dictate just how "good" the system will operate under given conditions, and just where the quirks may show up when the system is modified or placed under high demand. 

Anyways, those are my thoughts after having read through the thread thus far.


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## Grinder (Dec 18, 2016)

FlyingEagle said:


> The last page of responses, along with a multitude of earlier responses in kind, have summed up the issue with large current draw in short bursts or longer, as it relates to the vehicles electrical system and its ability to handle the extreme draw that it was not designed to. Yes, it can handle up to a certain current level (or at least to the level of a hot saturated alternator/rectifier bridge/regulator assembly) whether controlled singularly internal to the alternator or external by a device or ECU. If you expect more, you need to design or reconfigure elements in the system. Great ideas about using a newer style of headlamp bulb and related control mechanism that is less prone to dimming as voltage varies, gets you a bandaid but will work just fine.
> 
> I don't see much more point to the thread if there isn't much more agreement on the OP's end, as taken from my point of view. I have seen a lot of great and truthful information posted here, and none of it is meant to demean the OP. I will backup my initial statement and only post thus far in the thread, with the fact that I am a licensed automotive service technician and work with these systems on a regular basis. It is actually kind of nice to sit here and see so many people from other walks of life, who are able to live and breathe well beyond the daily experience of those deep in the repair business.
> 
> ...


Great stuff! Thank you!


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## FastKat (Feb 5, 2017)

Thanks guys. I am good to go. Grinder -
no need to further burden yourself with my dismissive attitude!


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## Grinder (Dec 18, 2016)

FastKat said:


> ...I am good to go. Grinder -
> no need to further burden yourself with my dismissive attitude!


:laugh::laugh::laugh::laugh::laugh:

I'm happy to let this thread speak for itself.


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## Alain93 (Mar 6, 2017)

FastKat said:


> Meh, I doubt it. Certainly not on a brief testing basis.
> 
> 
> 
> You can take just about any newish car, start it, disconnect the battery, and drive it from NYC to LA with all the lights on, fans on full blast, defrosters on, etc., and be fine. I understand that a sound system can be demanding though I'm not sure if it is practically different than the above.


Do not disconnect the battery while the car is running, especially with newer car, you may damage the ECU. It was OK back in the days, before 96 or 97, not anymore. 

Sent from my SM-T530NU using Tapatalk


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## lurch (Jan 20, 2014)

Nice to see another liscenced mechanic " flying eagle " and you are spot on. 

To the OP :
You will NOT make it to LA. 
Removing the power cable puts the alt into " full field " mode, meaning 100% output
and duty cycle. The alt sees a " low Volt " situation and asks the rotor to turn on 
full blast with no breaks. 
Eventually the stator coils melt down or cook the epoxy resin off the windings and short. 
That alt will be red hot in about 50 miles, depending on the ambient tempurature. 

It will also cook other delicate electronics in the car as there is too much voltage
surging throughout the entire system. So when the throttle position sensor melts and
the multifunction switch in the steering column melts and the ecu finally gives up, your
trip is over. 

just sayin ....


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## sirbOOm (Jan 24, 2013)

This thread is a disaster. End! 

You connect your amps to the + terminal of the battery - directly. Not after factory wires. Not at the alternator. Not anywhere else. Figure out how to do it. There is no reason to be concerned about whether your amps pull some power from the battery or not. They will, especially if you have a variable output alternator. Get over it.

Moving on...


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