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I can assure you that there is more than enough information above to answer the question correctly. Like I said, it's not the easiest question I've asked. If you can't answer it, then that's OK. Follow the thread and you'll learn how TO answer it.

the question is fine, you are asking on a community that just overbuilds the shit out of things, so most would just go over what is need rather than just hit the mark. But i enjoy the questions.

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Mechman 370 alternator which outputs 200+amps at idle and 370 at speed.

(1) XS Power D4900 (1000CA and 80Ah for starting the vehicle)

(3) XS Power XP2500 (CA doesn't matter their supplemental and 100Ah per battery)

I based this off of Ah which is probably wildly wrong but whatever.

So yea I am guessing 375 amp draw for 1 hour....and the 4 batteries could handle that when fully charged. Knowing the wattage and whether its a 12v/14v/16v system would help too.

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ok to the first problem at hand.

-To be able to play his music as loud as it will play while driving the vehicle without having voltage issues.

With this question i am going to assume that for the most part Takedown504 will be moving in his vehicle and that for 80% of the time his RPM’s are at cruising revs, 2000RPM at least, therefor giving us full amperage potential in terms of the alternator’s rated output. Since we also know that Takedown504’s car will draw 75 amps to be completely sustained at any given time while on, and that his sounds system amplifiers will require a max draw of 300 amps, he will need to be able to sustain a constant output amperage of 370 amps from the alternator in order for there to be no voltage issues. Since this isn’t a perfect world and the alternators output amperage and voltage are constantly spiking and dipping (due to RPM changes, and the change in amp draw etc) Takedown504 will also need to upgrade the primary battery under the hood in order to provide the burst amperage that may be needed when the alternator isn’t able to produce 370amps of output. So products needed: 1. 380amp alternator (given it fits, the exact vehicle wasn’t given) 2. D3100 12volt AGM battery (once again depending on group size required for primary battery)

now for the fun question

-to be able to play his music as loud as it will play cleanly while parked and the engine is not running for one hour.

So when i originally started to answer this question i began searching through the best Lead-Acid/AGM car audio batteries to determine the appropriate bank that would be needed in order to sustain a 300 amp continuous drain for 1hr. But even with the best of car audio batteries, the main problem with lead/acid and AGM that I kept running into, was that the degradation of power is relative to the speed at which you attempt to withdraw. And sadly with those batteries, its almost exponentially negative. For example a battery that is rated at 120ah, probably got that rating because it was able to hold a 15 amp draw for 8 hours, and not actually a 120 amp draw for 1 hour like some may think. So when it comes to Takedown504's problem, just having 3-100ah batteries, or even 5, or 7 for that matter, would not matter because the amount being drawn from them in such a quick manor (1hour continuos) would significantly shorten not only their life span, but their ah rating. And we know that because of Peukerts law, which says the faster you attempt to discharge any lead/acid type battery, the less energy you can potentially get out of it. Sometimes up to 60% of its capacity can be waisted/lost just from amp draw over its rating. Also with these batteries when fully charged, the batteries have a resting voltage in the mid 13s, but as amperage is drawn and the battery loses charge, say 50%, the resting voltage will also drop substantially, and since we want good voltage for 1 hour without charge we cannot expect to use all of the batteries potential power. SO we’re looking at double up at least again and where we were was already “overboard”. So in there lies the problem. And after some research i think i found the solution for this part of the question. In order for Takedown504 to be able to sustain music for 1 hour without charging, he would need to install 2-200ah Lithium Ion batteries in the secondary location of his vehicle, connected through either an isolator or relay directly to the alternator. Because of the design of Lithium type batteries, the downfall that plagues lead/acid batteries (Peukerts law), is virtually nonexistent. Meaning not only can you draw more current over shorter period of time and expect the same factorable amp hour rating, you can also expect the same voltage practically no matter the percentage of battery life remaining (we’ll say 80% of battery is usable). it will continue to supply a constant amperage, and voltage until the battery is completely drained, unlike lead/acid in which voltage/amperage drops constantly until it dies (doesn’t matter we want good voltage). So for Takedown504, if he had 2-200ah (or 4-50ah etc etc) lithium ion batteries, he could knowingly support his system for 1 hour easily with a 300amp draw (300ah), and be confident that once that the time was up, the batteries would have enough juice to be safely recharged by the alternator. here’s one of the batteries i used when doing these calculations http://www.lithiumion-batteries.com/products/12v-200ah-lithium-ion-battery/

That also shows a discharge graph and RC rating which verify my thoughts on sustaining voltage constantly. I know people are freaked out about them but hey, you wanted an answer, and mathematically it works.

glad i finally got to reading something recent, i always search and find past questions and topics i would have liked to try my 2cents in but then i realize they’re years old so I’ve just silently been learning as much as possible. :good:

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I like tboorn's idea of "3-100ah batteries, or even 5, or 7"

I'd do a minimum of 4 100ah batts. But here is where I cheat.

You stated he wants to play for an hour engine not running. So here is what I do is sell him 2-3 portable RV 12v 10amp solar panels to keep the batteries charged.

And the trim on the panels must be painted black and gold :)

Edited by Smoove
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I will do two calculations due to one factor not being said and that would be the nominal system voltage and that plays a major factor when selecting the engine off mode. So I will base off of 13.8v and 12.6v for running vs not


First would be to figure out what the system and truck would use as a total amp draw


so it would be 300a + 75a = 375a while running.


then to convert from amps to wattage 375a X 13.8v = 5175w needed while running.


and then to play 1hr on battery alone would be just 300a due to all other power using devices are off and that would be


300a X 12.6v = 3780w needed while truck off


to maintain 3780w for one hour you can visit a site like this one listed to calculate the Ah of the battery vs the watts consumed.




Based on my numbers you would need 760Ah worth of battery storage to play 1hr with truck off. I did tweak the numbers a little on the calculator and used 12.6v X 300a to get 3780w where their calc only used a constant 12v


Now seeing that we would need 3780w in reserve and 5175w while driving we can now figure out the charging aspect.


With the stock alt able to produce 140a you would need to only come up with 235a to produce enough power for the system to run while driving. But with that being said you will not get 100% output all the time from the alt(s) due to heat and other variables so I would step up to a 300a to provide enough power to run the system and also charge the battery bank.


So here are my system plans. oh and the batts are all AGM's not Wet or Gel.


Battery bank = 760ah

140a alt + 300a alt (If dual alts can be done)


or


Battery bank = 760ah

Largest alt that will fit in his vehicle. (If dual alts can not be done)

Charge the battery bank to make up for the charging system short comings if the biggest alt does not meet the required power to run the system AND charge the bank.

 

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See, I told you there were some good thinkers here. However, no correct answers yet.

This is a multi-part problem. In order to answer correctly, you need to think about how to arrive at the solution versus the solution itself.

Tony Candela - SMD Sales & Marketing
Email me at [email protected] to learn about becoming an SMD Partner!

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Lets start with required current.

we need 75A to run the car day and night continous. i am assuming this is with all accessories on. idle vs ont idle i assume this wont change much for lack of argument. ill also assume we can get alternators to maintain a consistent voltage so amperage remains consistent for accessories.

so on the stock system we have 140A (stock alt) - 75A to run the car and accessories. That means with stock electrical with all the best cables in the world, we have 65 Amps remaining for extracurricular activities. I assume the stock alt is a hot rating since OEM alts usually are hot rated, not peak rated like most.

next lets specify our extra draw. So these amps need 300A of current to produce clean output. anyone with that much draw is going to be asking for a substage so ill assume the amps are class d. ill also assume these amps are not perfect and have an efficiency rating. lets just say of around 70%. considering they are wired to 1 ohm.

so if we need 300 amps clean to the point, after 70% efficiency consideration, we will need to feed these amps approx 430A to keep them happy. if the 300A requirement accounts for efficiency well then we need 300 amps.

next key to the puzzle. two things, average draw, and also duration.

To be able to play his music as loud as it will play cleanly while driving the vehicle without having voltage issues.

- To be able to play his music as loud as it will play cleanly while parked and the engine is not running for one hour.

on music, the average draw will not be a consistant 300 amps. the general rule of thumb for music is about half of the maximum continous draw.

so, we are working with approximately, 150 amps (if efficiency is included), or 215 amps (if efficiency is not included).

thus we only have a 140 amp alt running the car with 75A accessory load. another thing id want to point out is the fact that once car is on, the battery is a load on the system. depending on state of charge of the battery, the battery could be 5-30A load in addiiton on the system, i assume that was accounted for in the 75A idle draw. Any way.

While the car is driving, with stock system, we only have 65A remaining. with a 150-215 A requirement. so while driving, if playing music, we have a 85-150 amp deficit.

so the first step would be to upgrade the alternator. the type of car will determine how large of an alt will fit. from my personal experience not many 300+ alts do well at idle. So i would opt for a high quality 270-290 amp unit (cold rating most likely). This will give us a solid 225-250 HOT amperage output. even if it is 225 HOT and the 300 Amps account for efficiency, this 225A Hot unit would be able to support the system at set voltage on music.

My next question would be to see if he can run a dual alt setup. if its a truck you more than likely could run a dual alternator setup and the stock would give even more head room, especially if the 300A did not account for amplifier efficiency.

next we need stored power for when the car is off.

so i assume when the car is off that 75A load is no longer present.

so we have 300-430 amps but on music we are looking at 150-215 amps.

so we need 2 batteries at 75ah @ 1C to be able to support the 150A load for an hour or 3 70ah @ 1C to be abloe to support the 215 amp load for 1 hour.

that will deplete the batteries from a full charge to dead, and he wouldnt be able to start the car.

so in the end, I would put 2 100 ah @ 1C batteries for the 150 amp draw or 3 80ah batteries for the 215 amp draw not including efficiency.

so in all

1 270-290 Peak rated alt (does 225-250 at driving speeds), this will cover 300 amps after efficiency calculations.

1 270-290 peak rated alt (does 225-250 at driving) and the stock alternator, will cover the system if effciciency calcs were omitted.

or if he didnt care about idle performance which i dont see why he wouldnt,

you could do a single "370" amp unit. and that would do around 300-320A HOT and that would cover the whole system and car regardless if efficiency was included or not.

2 100 ah @ 1C batteries for the 150 amp draw (included efficiency). enough to start car after the hour.

or 3 80ah batteries for the 215 amp draw (not including efficiency). enough juice left to start the car after.

I forgot to mention the stock battery, I would also recommend to leave it in as extra security to start the cAr. Design the batteries in rear to support whole system alone and be able to start car still just in case that hour runs a little over.

also if it were me i would add a bank of super caps to stablize voltage and create an extra buffer between the alternator and battery bank so the batteries would last longer. but thats just me. it wouldnt really be necessary if batteries are quality, but it would help the system.

and i think i covered it all.

Edited by Bump4life
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Very nicely done and a very thorough explanation as well. B4L identified all of the clues perfectly and addressed the problem at the core. About the only thing he overlooked was the additional current required of the additional batteries added to the system. Yet, he did account for that in his somewhat generous estimate of the "5 -30 Amp load in addition to . . . "

In short, here is the process:

Amplifier Current Consumption * Duty Cycle of Music > arrive at total current required of audio system at maximum output

Total Current required of Audio System + Current required of stock Accessories > arrive at total current of audio system and accessories required with engine running

Amplifier Current Consumption with Music factored with the length of time desired to play audio system with the engine not running > arrive at total AH rating of batteries required to support

Current required to maintain a surface charge on said batteries + total current of audio system and accessories required with engine running = Total Current Required

Total Current Required > Size of Alternator, Cables, etc.

Sir, email me your address (link below).

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Tony Candela - SMD Sales & Marketing
Email me at [email protected] to learn about becoming an SMD Partner!

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:ph34r: (in the back seat lurkin for knowledge)

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