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Electrical System Capacity Question

  #1  
Old 10-16-2013, 02:11 PM
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Default Electrical System Capacity Question

Hi all,

I drive a 2009 Sedan, 2.4L EX-L without nav. I'm planning a comprehensive A/V upgrade project, and I'm trying to figure out just what I'm working with in terms of the charging system. If I'm not mistaken, it looks like I've got a 130A alternator. The question is, how much of that charging capacity is taken up by the car's systems? I'm looking for a worst-case-scenario figure, that is to say parked with the engine idling, A/C on high, heated seats on high, high beams and fog lights on, everything except for the radio (since I'm replacing it, I'm not interested in how much current it draws). I'll likely end up measuring for myself using a shunt, but it'd be nice to be able to save myself the trouble.

Thanks!
 
  #2  
Old 10-16-2013, 02:36 PM
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40% is your usual usage. leaving you about 60% reserve.
 
  #3  
Old 10-16-2013, 03:40 PM
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Not really the answer I'm looking for, but thanks for the reply. Let me rephrase.

The alternator has a peak output of 130A. At idle, assuming 40% output, output is 130*0.4 = 52A. The question is, how much of that 52A would be left over if everything in the car (except for the radio) is running and I'm not going anywhere? And for that matter, is 52A really the correct figure for my car's idle alternator output? For example, if the car's engine, battery and other systems together draw 20A, then 52 - 20 = 32A. That 32A figure is the magic number I need to know when I'm deciding which speakers and amps to install.

I understand that average usage will be less, but I live in a city where I spend a lot of time sitting in traffic jams, often at night or in very hot weather. The last thing I want is for my battery to run dry because my alternator can't keep up, so for me this figure does in fact become pretty relevant.

P.S. - Yep, I've considered adding a second battery, a capacitor or a high-output alternator, but if I can avoid any of these complications I'll be much happier.
 

Last edited by Gerhard01; 10-16-2013 at 03:42 PM.
  #4  
Old 10-16-2013, 05:10 PM
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you have a 60% reserve, meaning if everything on the car is running at once you are using 40% of your alternators charging capacity. but it depends too on the amp hours and cold cranking amperage of your battery. If you want to know your alternators idle amp output you will have to have it bench tested. the alt on your car and the alt on another are going to match exactly.

couple that with the fact that current draw of the stereo will not be steady and will have a high draw when bass hits and a low draw when the bass is not hitting. the alternator can charge when there is not a high amperage draw and the battery can sustain the power when there is. it will not be pulling directly off of your alternator but off of your reserve capacity instead of the alternator.

Generally speaking if you stay under 1000 watts rms on your subs and 500 rms on your highs. you should be fine with the factory charging system.

Now the RMS printed on your product box is not true rms. you will need a clamp meter to find true rms. the box does not account for box rise on the subs or any resistance you may pick up through wire.

the most effective way to find out if you will for sure need another battery is if you have voltage drop you will need another battery. because of your cars eld system you will not be able to tell if you have voltage drop very easily because the car cuts the voltage when it does not need 14.4 volts.

the speakers do not matter at all when deciding if you need to upgrade your electrical. all that really matters is the amp. how many amps are you going to be running and how much power RMS are you shooting towards pushing and what amplifiers? some amps are far more efficient than others.

If you told us your goal we could probably help more. Are you trying to break glass, do you want a good solid bass note, do you want to be louder than factory sound better than factory?

edit: you will also not run your battery dry. any decent quality amp will cut off when the voltage gets low. so the voltage drops too low the amps will cut off and when the voltage gets up they will turn back on. now if you were ever to experience this it would be wise to turn the subs off for a while and let it charge.

also when sitting in traffic are you going to just be slamming your stereo the whole time. you dont see high amperage draws until you are really pushing the stereo. the factory stereo is probably only running about 40 watts total at full volume. so are you going to be running 1500 watts when just sitting in traffic? chances are no. you are going to have it at a "reasonable volume" and only be pulling about 200-250 total tops. which is going to be a very small amperage draw. for example I am running 1500 watts per sub. when I clamped them each amp is pulling 17 amps when the system is slamming and moving my windshield. not really sitting in traffic volume.

In short I am sure someone like KHA could answer your question with a direct answer, but that knowledge is just a fun fact and not all that useful in a practical situation when you are making decisions based on theory and how things should work with 100s of variables that are unknown at the time and wont be know until after the fact. then once they are known they all affect each other so it is not a simple change one thing.

the best way for me or someone else to help you is to tell us how much power you want to run.
 

Last edited by neophyte; 10-16-2013 at 05:25 PM.
  #5  
Old 10-16-2013, 08:26 PM
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Well I'm not looking for a lot of volume. I'm not the kind of guy who shares his music with half the city or is interested in going deaf by 30. My upgrade has three goals: first, integrate all of the latest A/V technology that the '09 Accord is missing. Second, reduce noise, vibration and harshness (this will be handled through soundproofing and vibration dampening material, so I won't cover it further here). Third, maximum improvement in sound quality with maybe a modest increase in SPL.
Here's the rundown on the system as it stands now, with links to the manufacturers' pages for each of the items:


1. Head unit - Alpine ICS-X7HD. This will give me HD radio, SiriusXM, a backup camera, Bluetooth, USB and the ability to use an iOS or Android mobile device to supply streaming audio/video and navigation. I'll install the USB port in the covered center stack storage compartment and add a Beanco Technology Mobile Home unit to the right of the shifter to make using the phone hands-free easier. My mobile devices will be a 64GB iPhone 5S and an iPad 5 (can't wait for that to come out).
Alpine Electronics of America, Inc.
Mobile Home

2. External DSP - At first I was planning on keeping the factory head unit, so I was planning on adding an Alpine PXA-H800 signal processor, but with the Alpine head unit I'm thinking this will probably be unnecessary?
Alpine Electronics of America, Inc.

3. Speakers/Subwoofer/Amps - I'm still trying to figure out exactly what I want here, and just like with every other part of this project I'm definitely learning mostly about how much I don't know. A lot of the reason I've been asking about the car's charging system is that I'm using that information to help determine what I can fit to my car. I've been toying around with the idea of something kinda like this:

-Front speakers/tweeters: Focal K2 Power 165 KR2 6.5" 2-way components, 80W RMS at 2 ohms
http://www.focal-america.com/wp-cont...65KR2_SPec.pdf

-Rear speakers: Focal K2 Power 165 KRC 6.5" coaxials, 80W RMS at 4 ohms
http://www.focal-america.com/wp-cont...65KRC_Spec.pdf

-Subwoofer: Focal Utopia Be 21 WX 8" multimagnet subwoofer, 250W RMS at 4 ohms
http://www.focal-america.com/wp-cont.../21wx_spec.pdf

-Amplifiers TBD, but obviously a 4-channel for the speakers and mono for the subwoofer.


I like the idea of this setup or something comparable, but I could be missing something. Also, I'm a little concerned about some of my speakers being 2 ohms and the rest 4 ohms, would this cause problems? And finally, while I plan on listening to speakers in-store and in-car, I'm not sure that the difference in performance between these speakers and something a bit cheaper would justify the extra cost. I'd probably wind up with a nasty case of buyer's remorse, but hey if I'm only planning on doing this once every several years I'm sure I can rationalize it.........um...right?
 
  #6  
Old 10-16-2013, 09:15 PM
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with what you have there assuming you power them at their recommended power, your factory electrical system would be more than enough. If anything just upgrade the factory grounds (big 3).

Focal makes some nice products and with that amount of power your will definately gain some volume. if you are going for sound quality just puts some mid bass speakers in the rear deck. the tweeters will throw off your soundstage. the difference between the 2 ohm and the 4 ohm wont matter too much. just have to make sure your gain is set properly not to overpower them. It will have some affect of the dampaning factor of the speakers but for a daily driver I dont think it would be a whole lot.
also the difference in speakers in the store and in the car will probably make more of a difference than the slightly less expensive speakers. buildings are a lot more accoustic than cars are.


and If you are wanting a high sq an external processor is a must. and a crossover with a more specific setting than what is available on the amp is a nice feature too.

Sound quality is not really my thing. check out Keep Hope Alive's build thread. he is an sq and electrical genious. at one time I was focusing on building an sq car but I decided to switch to spl. I may be building an sq vehicle soon but as of right now my experience is limited.

Keep hope alive you wanna chime in on this?
 
  #7  
Old 10-16-2013, 10:58 PM
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thanks, neo, for filling in.

excellent questions here. I can tell you have at least the fundamentals of electrical knowledge if you recognize you can measure current with a shunt. but measuring current used doesn't tell you what the capability is. the alt output will respond to the load presented. you can turn everything on in the car and measure that load and you'll probably find between 20-40A of draw depending on lights on vs. off. note that Honda (like most) only put what they need into the car and they do not plan on giving you more than you need.

Also note that Honda uses the Electrical Load Detector (ELD) to measure ignition current and the powertrain control module (PCM) uses that information to decide if it is ok to turn off the alternator field current (thus turning off the alt). I have devised a bypass that is detailed in this section. we can discuss electrical infrastructure in more detail as that is the true nature of this post, but you mention other aspects that I want to discuss quickly.

You have chosen some nice equipment. I would persuade you to audition Hertz Mille next to Focal, i've heard both and Hertz wins in my opinion. Audison makes excellent amplifiers as well.

I have used the H-series processors from Alpine, most recently the H701 (predecessor to the H800). You still need the RUX-C800 controller and that is an $800 processor/controller combo that is indeed awesome if you want to run the system active (i.e. not use passive crossovers). The head unit you chose (also a nice piece) does include time alignment and a decent EQ which can be sufficient with passive crossovers and a good installation. I know, because i have a similar headunit (same processor internal) and am using it without the H701.

Getting the H701 depends on your budget and goals. If you want additional tuning capability and are willing to spend more on the processor and additional amplifier channels, go for it as you will be pleased. Note it adds $1500 to the total package once you figure hardware (processor + additional amplifier channels + infrastructure, and wiring). Only get rear speakers if you run a processor, and only run midrange drivers that match the front. don't use rear coaxial as we do not want any tweeters behind us. i can delve more deeply into the aspects of localization and human hearing if you wish. with this system, your goal should be recreation of an accurate sound stage in the front of the vehicle.
 
  #8  
Old 10-16-2013, 11:23 PM
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as far as electrical capacity goes, the simple answer is no. and I contradict myself here when in your first post I said it would be fine. I've further taken into consideration you desire to sit in traffic with full resources. no, the stock electrical system is not capable nor designed for an external sound system like you want. basic systems as neo described and as I assumed you wanted do not need much power for modest volumes. when you start getting into high end audio + long periods of idling, you start wanting a more robust electrical system that provides dynamic range (which means the amplifiers require bursts of current, bursts that the stock alt under load cannot cope with).

i encountered this recently with a 2005 Scion tC build. It is a reference-quality system used by a recording engineer and acoustics co-worker/friend.
KHA 2005 Scion tC with Audison and Hertz

Running a single Audison LRx5.1k his stock 100A alternator was woefully incapable despite a good battery and wiring upgrades. So he purchased a 160A alternator from Quality Power. Still not enough. Then he upgraded to a 240A alternator and his voltage drop problems were solved. But shortly after the car started throwing error codes because the charging curve was different and the ECM was getting voltages it didn't expect (the new alt reached 14.4VDC at a lower RPM than stock). Instead of reprogramming the ECM, he removed the alternator. Instead, we are going to do a bank of six 3,000F ultra capacitors - the same that I have in my car and have done in other cars in lieu of upgraded alternators.
Specifically I use six Maxwell BCAP3000-P270-K04 wired in series
http://www.maxwell.com/products/ultr...es_1015370.pdf

The Big 3 wiring is certainly a must and is harmless to the vehicle. Essentially this is just reducing resistance in the stock charging system.

You will want to plan on supplementing the electrical system otherwise you will lose musical dynamics.

The standard capacitors you see (1F or 5F) are too small to be useful despite the marketing behind them.
High output alternators are worth the investment and you should not have any electrical issues with a high output alternator on the Accord (once you bypass the ELD).
 

Last edited by keep_hope_alive; 10-16-2013 at 11:59 PM.
  #9  
Old 10-16-2013, 11:41 PM
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Originally Posted by Gerhard01 View Post
I like the idea of this setup or something comparable, but I could be missing something. Also, I'm a little concerned about some of my speakers being 2 ohms and the rest 4 ohms, would this cause problems? And finally, while I plan on listening to speakers in-store and in-car, I'm not sure that the difference in performance between these speakers and something a bit cheaper would justify the extra cost. I'd probably wind up with a nasty case of buyer's remorse, but hey if I'm only planning on doing this once every several years I'm sure I can rationalize it.........um...right?
Do not worry about impedance differences in speakers when they are on different amplifier channels. In general, higher impedance is preferred as amplifier damping factor improves and THD reduces.

There are HUGE differences between speakers. Each one by each brand, in each line, sounds different. But in order to get the most out of any speakers, the installation is vital. Note with home audio you are paying for a package that has hundreds or thousands of hours in R&D with the enclosure. In car audio you are the designer and you buy raw drivers and then construct the enclosure and listening environment.

I have built car systems with budget raw drivers and active processing that most people would consider outstanding. but it required hundreds of hours of effort and testing multiple driver combinations (i have 10 speaker locations in the front of the car - 5 per side that i used to experiment with a 3-way active front stage).
Now, I have one excellent 2-way component set and that is all I need. The main problem with a 2-way system and stock door locations is that the door woofers are not aimed back at the listening position. The result is an off-axis response that limits woofer response above 3kHz (something I have measured with a variety of drivers). The problem this creates is that it forces the tweeter to play down to 3kHz before it's crossover takes over, which pushes audible response down to 1kHz or so (assuming 12dB/oct slope that is common to most passives and devices). This causes the tweeters to sound harsh and also messes with localization and the sound stage. The fix is to run a 3-way system with a dedicated midrange located on-axis that allows you to pus the tweeter crossover to a comfortable 4-5kHz. Fine and dandy, but a lot more work fabricating a new speaker location.
The Hertz Mille woofer is dramatically different in that its hyperbolic cone has excellent off-axis response. I've measured the woofer playing to 6kHz before roll-off when measured at the listening position (headrests). This is the only woofer i've seen do this and it's due to the cone design. Further, the tweeter in the set has air passages and a removable rear chamber to absorb rear wave from the tweeter dome (also a rarity). This chamber lowers the fs to 960Hz which extends usable response down to 2kHz. While you don't want to play it that low for several acoustical reasons, it does offer a lot of flexibility.

An installation that incorporates diffusion and absorption, damping and transmission loss to control the rear wave is the goal. Speaker locations need to be adjusted based on the polar response of the drivers and flexibility in crossover points. lastly, reflections and phase interference are also factors to consider. I have my own ways of achieving this, and i steal from my work in acoustics.

You mention lowering road noise, I have found some products that are affordable and also very effective. I have shared them in the sticky on deadening.
 
  #10  
Old 10-16-2013, 11:53 PM
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Originally Posted by Gerhard01 View Post
Hi all,

I drive a 2009 Sedan, 2.4L EX-L without nav. I'm planning a comprehensive A/V upgrade project, and I'm trying to figure out just what I'm working with in terms of the charging system. If I'm not mistaken, it looks like I've got a 130A alternator. The question is, how much of that charging capacity is taken up by the car's systems? I'm looking for a worst-case-scenario figure, that is to say parked with the engine idling, A/C on high, heated seats on high, high beams and fog lights on, everything except for the radio (since I'm replacing it, I'm not interested in how much current it draws). I'll likely end up measuring for myself using a shunt, but it'd be nice to be able to save myself the trouble.

Thanks!
re-reading this i see you mention heated seats, those can be ~10A along. high beams and low beams can be ~15A (assuming four 35W bulbs), A/C can pull ~20A with the compressor on. That can put expected draw to between 40-50A.

the alt output capability varies with engine RPM. then the curve increases to the rating which it achieves around half of the alt RPM capability. Curves for the Honda S2000 look like this (achieves rating at 5000 RPM):



the general idea is that you cannot apply a linear approximation (i.e. percentage) to the alt capability because the curve is logarithmic.
 

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