few ? about different things .

[big scott]

hi guys,

was going to make a few threads but decided to just ask in 1 thread.

1- how to calculate how many alts i would need for my system. ?

2- if you wire a sub for 1 ohm will the amp ever see that 1ohm? meaning there box rise.

see was thinking of wiring 2- d2 to 0.5 ohm and was wandering if the amp will ever see the 0.5 ohm because there box rise.

3- im a little confused as i have read both ways. but from what i understand if im not going to run my system with my truck OFF then i dont need extra battery's/caps right ?

i may add to the list but right now i cant think of anything else.

Click to read more...

 

[bbeljefe]

hi guys,was going to make a few threads but decided to just ask in 1 thread.

1- how to calculate how many alts i would need for my system. ?

2- if you wire a sub for 1 ohm will the amp ever see that 1ohm? meaning there box rise.

see was thinking of wiring 2- d2 to 0.5 ohm and was wandering if the amp will ever see the 0.5 ohm because there box rise.

3- im a little confused as i have read both ways. but from what i understand if im not going to run my system with my truck OFF then i dont need extra battery's/caps right ?

i may add to the list but right now i cant think of anything else.

It doesn't matter how many alternators you have, it matters how much current the one (or ones) you have can supply. Seventy amps per 1000 watts would be ideal, although not many people get to that point. As for batteries, yes, you do need them regardless of whether you're going to play the system with the vehicle not running. Fifty amp hours per 1000 watts is ideal for batteries but that and the alternator requirement I mentioned aren't deal breakers so you could get by with a little less if your alternator(s) are over sized but you'd need more if they were under sized.

With respect to impedance rise... all loudspeaker drivers, whether they are subs, mids or tweets, present impedance rise when in motion and that happens regardless of where they are mounted. They don't even have to be connected to an amplifier in order for impedance rise to take place. All that has to happen for a speaker to create impedance rise is that the coil moves relative to the magnetic field it is in. That said, amplifier designers already understand that their amplifiers will rarely, if ever, see the lowest impedance they rate them for when they rate them. Thus, when a manufacturer rates an amplifier at 1Ω, they are rating that amplifier at 1Ω nominal impedance. What that means is that the amplifier can handle the normal impedance fluctuations of a loudspeaker load that, when at rest, equals 1Ω or higher.

In simple terms, you can't trick the amp or the engineer who designed it by putting your subs in a box. Moreover, there are a lot of different factors that determine how much impedance rise will occur with a loudspeaker so the term box rise is not really accurate. It's true that the box will have some effect but it's also true that the environment outside the box will have an effect, including the barometric pressure, the temperature and the elevation.. and we don't say barometric pressure rise, lol.

All that said, if you're seriously concerned about the safety of your amplifiers, don't run them at lower than recommended impedances. Of course, amp manufactures will often rate their amps conservatively to cut down on warranty claims so your amp may in fact be capable of handling a .5Ω nominal impedance while only being rated for 1Ω but, that risk is on you for the most part.

Lastly, and this kinda ties back into the other two questions... if you do run your amplifiers at lower than rated impedances, you need to over build your electrical system because the rules of thumb I listed above are for average class D efficiencies. And when you're wired below rated impedance your amps will be less efficient. Much less efficient in most cases and that means they will require a lot more power in order to keep from self destructing.

 

[brian84corvette 10+ year member]

when i build i use the math ratio 100 watts to 10 amps

and there is an alliance between alternators and batterys - my talks with mylows10 have lead me to understand the need to have reserve battery in equil portion to alternator power - at first i thought it was just all alternator and batterys did not matter - there have been people who can run their stereo systems off of just alternator power - to prove the point that it is capable of being done, but there is a nice alliance between battery reserve and alternator power that helps out during a huge system when playing full tilt.

im running a single singer 320 hair pin alt. it produces 220 amps at engine idle - and 320 amps at 2k rpm i also have 410 amp hours worth of resrerve batterys in the truck - so by my math 730 amps is my absolute max draw capable... if my system tries to draw more than that - it just cant there is no where for power to come from.... lucky for me my system is only going to be around 6k watts total out put at its max - and in daily music and ground pounding i would imagine 5k watts output is more realistic. so i have a bit more electrical on tap than what i would need at the minimum - wich is good as i plan to demo alot at shows.

 

[big scott]

thanks very much for that info.

as for the amps ohms i was just thinking about box rise. but what you said makes cents.

and as for batterys, see thats what im saying one person says no you dont need batterys,, and others say if you plan on playing you system with truck off then yes you need batterys.

thats why im confused.

but you say i need then no matter what. right now im at about 3,500 rms but when done ill be at 6-7,000 rms total.

and about the alts. right now i have a 200amp alt and im at the max rms for this alt. hell at full tilt now in dipping in the lower 12v and i dont like it.

and going to put another alt, thinking about a 240amp . so ill have 2 alts. with 440amp total. and was wandering if thats enough .

 

[big scott]

when i build i use the math ratio 100 watts to 10 amps
and there is an alliance between alternators and batterys - my talks with mylows10 have lead me to understand the need to have reserve battery in equil portion to alternator power - at first i thought it was just all alternator and batterys did not matter - there have been people who can run their stereo systems off of just alternator power - to prove the point that it is capable of being done, but there is a nice alliance between battery reserve and alternator power that helps out during a huge system when playing full tilt.

im running a single singer 320 hair pin alt. it produces 220 amps at engine idle - and 320 amps at 2k rpm i also have 410 amp hours worth of resrerve batterys in the truck - so by my math 730 amps is my absolute max draw capable... if my system tries to draw more than that - it just cant there is no where for power to come from.... lucky for me my system is only going to be around 6k watts total out put at its max - and in daily music and ground pounding i would imagine 5k watts output is more realistic. so i have a bit more electrical on tap than what i would need at the minimum - wich is good as i plan to demo alot at shows.

ok good info. what batterys do you have?

im trying to figure out how many i need. and if 2 alts will be enough . with 2 alts ill have 440amp.

 

[brian84corvette 10+ year member]

if 2 alts are not enough - you can make up the diffrence in ( good ) batterys. - a good battery is low esr - to give off and take back in power at a faster rate than most batterys can.

the math formula of 100w to 10 amps is pretty good at rough guess on requirments

mid 12 volts is still acceptable. its anything under 12 volts is where it gets scarry with things getting burnt up.

the guys with big systems are not keeping above 13.5v playing full tilt unless they have an un limited budget to work with...

most normal people on a budget drop in the 12s and we are fine...

with my ddm2a (2500w @.5 ohm ) and my pair of mb quart discus 4 chans ( 1k each amp ) i was droping to 13s flat in my setup - and i believe thats because all 4 of my batterys will "rest" at 13.0 volts after a few days of the truck not being on - but there is a thing called float charge - where a battery will hold in the 13.75 + range as the alternator is putting 14.4 to 15.0 volts out - for a few seconds after that charge stops the batterys keep this float voltage and thats whats feeding the amps as heavy bass lines hit that drop voltage badly.

my singer alt charges at 15.0 volts ( its a bad to the bone unit ) so when im blasting and the voltage starts to drop - from 15.0 down to 13.75 volts is being fully fed by the alternator.. the batterys are there - but the alt is running everything... once voltage drops below 13.75 volts the batterys start putting off their float charge to feed in to the system along with the alternator... if the drop continues below 13.0 then the float charge is now worn off and the batterys are playng the system off of their reserve capacity - along with the alternator still adding what its capable of...

but

in most music - its not a steady tone of bass. it has pauses and breaks in it - wich allows the alternator to re float charge the batterys back up in between bass hits - and as long as the system does not dip in the low 12s for extended amounts of time the batterys will continue to be avalable for power draw for the duration of a few songs - to a few hours of music before needing re charge depending on certan things...

again

we are talking above normal stereo system stuff here in the 4 to 6k watt systems...

i can never say enough good stuff about my singer hairpin alternator - it has a incredable rebound rate. if i play a 35hz tone for 30 seconds and drop to 13.0 volts during that tone - the rebound of the voltage is almost instant... as soon as the tone is finished the voltage will spike back up to 15.1 or 15.2 volts at a much much faster rate than my stock alternator ever could.

 

[big scott]

ok that does make cents about voltage with batterys. ok i was on the right track meaning i have planed on getting about 4 batterys. i think with 2 alts. with 440amp total and 4 good batterys i should be good.

and my calculations was wrong.

ill be pushing about 11-12,000rms .

thats with 8 amps.

6- 6.5

4- tweeters

4- 15"

4 or 8 8" bass speakers

and was looking at the amps im going to use for my 4 15" and was going to run 1 amp per 2 subs. but i changed my mind. im going to get 1 amp per sub. so ill be pushing 2,300 rms per sub.

so now need to figure out how many battery ill need. as im not sure i can put 3 alts. on this engine. i think 2 is my max unless there a super big v-belt lol..

i will say this is getting expensive lol..

 

[brian84corvette 10+ year member]

just some quickie info on batterys -

normal wet cell car batterys and agm batterys should not mix because = normal car batterys will want to sit near 12.7 volts - and agm batterys will want to sit at 13.0 volts. the agm will always be trying to feed its charge to the wet cell battery - and this process wears out both of the batterys.

i had a wet cell normal car battery under the hood for a while - and 3 100 amp hour agm batterys in the rear all hooked together.

the agm batterys killed the wet cell up front and i was having issues i could not figure out. my dmm was reading 13.0 volts at the battery ( they were all hooked together still ) but i had weird drops when playing.

when i un hooked every battery from eachother - and let them sit for 3 hours... my dmm read 13.0 volts on all 3 rear agm batterys - but the front wet cell was reading 12.3 volts... and the next day it was reading 12.6 volts with out charging it back up. = that battery went bad by being constantly fed more than it wanted from the agms... but its low 12.3 resting voltage was pulling down the system voltage when trying to play "big"

since then ive added another agm up front - same size and kind as my 3 in the rear - and now they all rest at 13.0 hapily for days with out re charge.

good batterys have a low internal ohm resistance that allows them to give off a ton of power in a short amount of time.

this is strictly for explination purpose and not real numbers but....

if you were to touch the positive of a battery to the negative of the same battery and cause a dead short - this would allow the battery to give off its maximum avalable current and amps its capable of.

a wet cell can only give off power so fast - as its internal resistance is general higher than a good car audio agm battery.

so letts say you did that on your normal car starting battery and measured ... 250amps in exactly 1.0 second timed - a good agm battery might give off 400 amps in that same 1.0 seconds time because it allows power to leave the battery faster than normal batterys do.

this is great for car audio because the way car stereo amps ask for power is instantanious and sometimes for only split seconds.

during a big bass note - a car stereo amp may say to the elecrical system - hey give me 350 amps for .5 seconds duration so i can send that to the subs...

but if you only have one normal wet cell car battery feeding the system - the battery may say to the amp - thanks for your request but my maximum capacity is to give you 175amps in that .5 seconds time your asking for that power.... so you can see how the amp will need power but not recieve it due to the capability of the electrical system to feed what its only capable of doing....

i hope that makes sence

 

[hispls 5,000+ posts]

You'll never go wrong from going overboard on electrical, and if you plan to do anything other than play 3 seconds at a predetermined frequency you'll gain little and risk much by trying to run low impedance on your amps.

 

[big scott]

is a yellow top a wet battery ? thats what i have under the hood.

so if i add say 4 batterys in the back all amg audio battery should i get a battery Isolator ?

what i will do is replace the under hood battery as it is getting old but still work good. i just want to do this right.

 

[big scott]

You'll never go wrong from going overboard on electrical, and if you plan to do anything other than play 3 seconds at a predetermined frequency you'll gain little and risk much by trying to run low impedance on your amps.

i was just wandering if it worked that way. but i do see your point. ya my setup will only be daily and demos. so with the setup ( sub amps ) ill be running each sub at 1ohm the amps are rated down to 0.5 ohm but with my subs i cant run them like that unless i get d1 subs. but im not going to as i already have 1 d2 sub. so im going to stick with d2 that way i can run 1 amp per sub at 1 ohm . works for me lol..

 

[big scott]

ok heres 2 more ?

1- can i add 1 battery at a time? will i notice a difference if i add just 1 battery now ? or would i need to put all 4 in . and no i dont have 4 batterys right now or i would just install them. im asking to see if i have to store them until i get all 4.

2- this has to do with size of box to power. when i had my box build i was asked what kind of power i was going to use...

so lets say i had a box made for 1800 rms but decided to run say 2200rms with the same box.

what kind of difference would i see by adding more power .

so by adding more power sound the box be smaller or bigger ?

just wandering thats all.

th

 

[brian84corvette 10+ year member]

is a yellow top optima battery concidered a agm..... welllllll kinda but no at the same time... its a spiral cell battery... and ive killed my share of them. their internal resistance is not quite as low as it needs to be for car audio - even tho they are marketed to be car audio capable batterys - they are still pretty iffy.

in my experience - they do not do well with any tiny but constant draw in the car... mine would always be at 80% or less charge because of that and it was about one of the worst batterys ive had.

car audio type batterys are branded big names = over priced but good quality like xs power - and kenetik - stinger - odyssey - north star ext....

but there are also basicly re labeled batterys that are similar to those in no name brands that are also fairly good at car audio use. ( my favorite = deka intimidator )

my batterys are no name - china made and cost me $170 per battery no core charge delivered to my work for a 100 amp hour agm battery (63 lb weight)

idealy you would get all of your batterys you plan to run at the same time - from the same manufacture date - and from the get go they are all "matching" meaning that one hasnt been half used up yet directly linked to a newer one thats had no abuse.... you want them all to be as the same as possible...

but most of us here are trying to ball on a budget - so it is ok to get one or 2 and add one more as funds allow. the battery under hood takes the most abuse - as it has to deal with the elements and heat under there... newer batterys should go under hood - and older ones rotated to the back bank....

as for will you see a diffrence replacing the single yellow top under hood with a car audio type agm battery ? yes

it wont be a huge diffrence replacing just with 1 battery - but if you could swing 2 agm batterys of 100 amp hour ish ratings then you will definately see improvment much more than your current setup using the 1 yellow top.

battery isolator is a great idea. pain in the *** to install properly ( not being a bottle neck in electrical flow to the amps )

and about the 1800w to 2200w increase of only 400w will probably not be noticable....

i had a origonal gen 1 saz1500 wired at .5 ohm on my pair of re sx 18s and it was pushing them realley good - i thought swaping on a ddm2a at .5 ohm would instantly give me more loud because of the extra power ( about 600w more than saz1500 was giving ) but i could not even tell by ear if louder with either amp.

usualy to feel louder by a good amount you have to double power.... so if you had your box designed to play at 1800w and you jumped up to 3600w then you would need to re design the box to play off of that amount of power.... smaller boxes take more power than larger boxes - but larger boxes can be more efficent than smaller... it has to do with the air spring effect on the cone of the subs - as the cone moves in and out - the air traped inside the box will stretch and limit the movment of the cones - is good for mechanical throw - as subs could tear spiders / or smash the coils against the back of the motors - or even jump the coil right out of the motor if the box is designed to not limit the mechanical motion of the subs... but yeah 400w increase on the box should still be good

 

[akillj 10+ year member]

when i build i use the math ratio 100 watts to 10 amps
and there is an alliance between alternators and batterys - my talks with mylows10 have lead me to understand the need to have reserve battery in equil portion to alternator power - at first i thought it was just all alternator and batterys did not matter - there have been people who can run their stereo systems off of just alternator power - to prove the point that it is capable of being done, but there is a nice alliance between battery reserve and alternator power that helps out during a huge system when playing full tilt.

im running a single singer 320 hair pin alt. it produces 220 amps at engine idle - and 320 amps at 2k rpm i also have 410 amp hours worth of resrerve batterys in the truck - so by my math 730 amps is my absolute max draw capable... if my system tries to draw more than that - it just cant there is no where for power to come from.... lucky for me my system is only going to be around 6k watts total out put at its max - and in daily music and ground pounding i would imagine 5k watts output is more realistic. so i have a bit more electrical on tap than what i would need at the minimum - wich is good as i plan to demo alot at shows.

There is some misinformation here..

100 watts to 10 amps is only useful if you're charging at 10 volts. 100w / 10a = 10v

Realistically, if you want to calculate how many amps of alt you need, calculate it like this:

EXAMPLE:

5000w amp @ 1 ohm

70% efficient at 1 ohm

(5000 / .7) / 14.4 = ~500 amps

In this case, you would need 500 amps of alternator amperage to sustain that amp. Now, keep in mind, this would apply to a constant-tone scenerio. Music is not a constant tone. So you could get away with less than this.

Now, you said you have 410 AH worth of battery, and 320 max amps from your alt. Saying your max draw capable is 730 amps is only correct if you plan to run a tone for 1 hour (With the car revved up to optimal alt RPM)

410 AH = your battery's can supply 410 amps, for 1 hour. Or 820 amps, for half an hour. Or 205 amps, for 2 hours. So really you can supply way more than 730, that's not your 'absolute max draw capable.' Also keep in mind, the more current you draw (amperage) the hotter your batteries will run, thus lowering their efficiency and lowering their AH rating temporarily.

EDIT: Just realized that your 100 to 10 system would actually still apply to my example. You're not wrong, just that it would likely only work in monoblock amp situations, where their efficiency is relatively high. Anyone running their amp lower than 1 ohm where most monoblocks these days are rated, that system goes right out the window. To anyone else reading: running your amp at .5 does not instantly double power for free, as some people seem to think. The amp would become terribly in-efficient, run way hotter at that load, and tax your electrical even harder. If your electrical can't keep up with this added load, then it will be up to chance whether your alt or amp blows first.

I'm not hating on you, just clearing it up for anyone else reading //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[boxpunch]

hi guys,was going to make a few threads but decided to just ask in 1 thread.

1- how to calculate how many alts i would need for my system. ?

2- if you wire a sub for 1 ohm will the amp ever see that 1ohm? meaning there box rise.

see was thinking of wiring 2- d2 to 0.5 ohm and was wandering if the amp will ever see the 0.5 ohm because there box rise.

3- im a little confused as i have read both ways. but from what i understand if im not going to run my system with my truck OFF then i dont need extra battery's/caps right ?

i may add to the list but right now i cant think of anything else.

1- there's no set mathematical way to figure that out. If your vehicle's alt case can be built to 320a then you're covered to approximately 7k (with a few group 31 batteries). Although we have a customer with a 7k full tilt seeing 13v+ with only 4 kinetik 2400's and one of our 270's.

2- with music being dynamic (rise and fall) yes the amp will see nominal load and possibly lower. If you take a look at the impedance/frequency graph given with the specs of the sub you'll see there are frequencies where the sub's resistance is less than the nominal impedance.

3- if you're going to demo with the truck off all the time, you're going to need a big bank of batteries to support your system without a charging source. Then you'll need to maintenance charge your battery bank after to ensure proper charging levels as well as prolong the life of the batteries.