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Old 10-21-2014, 02:02 AM
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Got some noob questions for you guys, so don't hate...lol I've run different setups for 10 years or so but never anything big enough to worry about voltage drop. I am currently running (1)Skar ZVX 15 D1-4cube aero @32hz-Soundstream Lil Wonder 1700 @ 2ohms rated at 1200 which based on fuse rating is pretty accurate but have not clamped. I have a small cap, which I know is not a great solution, but I keep it in there mainly for the voltage meter. My stock alt is 150 amp(which is nice), stock+200cca batt, single run of Sky High 1/0 and I never drop below 13.2ish at full tilt even without a big 3 (don't hate, I know...I've got the Sky High and just got the lugs for it Friday). IMO that's not bad for now. So, my question is, when I move to an amp in the near future and put around 2k on the ZVX and 400ish on the doors, what should I do with the battery situation? My thoughts: Add a 2 or 2.4k batt to the back...Opt 1.Run both amps off this battery 2.Run the sub amp off this battery and the fronts off the front battery 3.Throw an isolator in the mix with Opt2 4. I'm an idiot and should scrap the ideas I have now...Sorry for the long post but wanted to make sure all the variables are understood. TIA guys any help would be appreciated.
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Old 10-21-2014, 06:14 AM
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I don't think it's a good idea to split battery power. I mean, wouldn't that just hurt the sub amp? (hurt as in provide less power to it, and dis-regarding any possibility of low-voltage hurting the sub, etc)

I'm sure the stock battery is helping a little. Certainly enough to not remove it from the sub amp completely?

I would see what the 2k you're going to get pulls first. Maybe look up some clamp numbers on it and see what the actual current draw is and then base your battery decision on that.

Maybe look into more efficient amps while you're at it. I'm not saying get a really expensive amp like mmats (those are pricey + super efficient, right?) but pay attention to what they pull from your electrical. And make sure it actually does that power that it claims. Some amps don't. And definitely get your amp clamped to see what you are actually pulling right now.

In my personal opinion, unless your lights dim (especially just from power windows and power door locks) or you upgrade the alternator to the point that the stock battery-to-alternator wire is heating up, catching on fire or popping fuses, I would not even worry about the big 3, at least for now. Focus on finding out what kind of numbers your current and future amps are doing
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Old 10-21-2014, 07:23 AM
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I agree that you might take the wait-and-see approach. It sounds like you have a pretty healthy charging system right now. You mentioned a single run of SH, which I'm assuming means you are grounding to the fame/chassis at the rear amp. If that's the case I would definitely upgrade the under-hood grounds. With a stock alternator there's probably not much benefit to upgrading the charging wire from the alternator to the battery, although that's more vehicle dependent.

For the battery situation: If you want to add another battery and don't plan on demoing with the car off (you shouldn't' be doing this anyway) you don't need an isolator. Even if you got one it would be hell on the alternator having to charge a near-dead battery after demoing as well as keep up with the car's electrical demands. From personal experience, I would completely ditch the stocker and replace it with a good AGM with as much capacity as you can afford and fit in the space. When you mix an older stock battery with a new AGM at some point the old stocker WILL die, and when it does you'll put a big strain on the alternator as well as the secondary battery. It might not be a big deal and you can just re-wire for a single battery or replace the stock with another AGM, but If it were me I'd save the hassle and just do a replacement. You might also consider adding the AGM to the rear for now and planning on saving a bit to upgrade the front battery in the near future before it dies on you.

For wiring: in a parallel circuit (which your 12v system is), voltage should remain consistently the same across the entire circuit. In reality there will be small difference at any given time due to the way the charging system works and resistive losses through the wire and terminations. You won't "even out" anything by wiring the amps up to separate batteries though. For the sake of ease and cost just wire everything to the rear battery. Make sure you are fusing after every + connection at each battery, so you should have a fuse at the front of the car close the battery on the line leading to the back, then another fuse as close the the back battery as possible on the same line (2 fuses on this line), as well as the appropriate fusing going from each lead on the rear battery to the amp(s).
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Old 10-21-2014, 06:08 PM
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Awesome feedback guys, I appreciate it. I heard using the isolator was only beneficial when using deep cycles and demoing with the car off so that option is out the window. Wiring everything to the same battery does make more sense for ease and really wouldn't matter because both batteries are part of the same electrical system to begin with so there would be no "evening out" of the strain. So...the plan I think that's gonna fit my wallet and setup is gonna be a back battery based on the strain I'm gonna pull with my new mono. Which I can tell you is either going to be an OPTI2k or Sk1500, wither way will be wired at .5...Thoughts on this?(meaning amp choice/experience with "power hungriness") Both will handle .5 obviously but one better than the other IYO? Also, when selecting a battery for the back I've heard it's a good rule of thumb to pick one based on with the amount of amps to match the amount of watts you plan to pull from it...true story? Thanks guys!
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Old 10-21-2014, 06:10 PM
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**watts you plan to put on it...sorry brain slower than hands
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Old 10-21-2014, 09:57 PM
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There's been a few threads here where people discuss how much battery you need to support a certain amount of watts. Really though there's no go way to estimate that. Lower internal resistance, higher short-circuit and cranking amps, and better plate design gives you better transient ability for burst of power, and being larger (more amp-hours) means you can provide power for a longer time before voltage dips too low. I'd say just get the largest battery (in AH) you can afford and have room for. As a matter of comparison I have a 93AH battery and stock 85A alternator supporting a bit over 2kw. Voltage stays above 13 even on long transient peaks unless I'm at idle when it will dip into the high to mid 12's. I also run my amps pretty conservatively though, and if I get my sub amp into a clipping sutuation voltage will drop into the high 11's. A general rule of thumb is to never let your voltage dip lower than the resting voltage of the battery, which should be about 12.8ish V.
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Old 10-22-2014, 03:01 AM
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Once again man great feedback! I'm seeing about the same numbers with running my stock+200cca battery and stock 150 amp alt on around 1200. My plan for the time is to leave that battery and add an 80-100ah battery in the rear. From the info I've picked up from you and graham, I think this should be sufficient. I know you said my under hood battery will go bad at some point but is it "bad" to just keep a regular auto battery under there paired with the rear AGM? Or is it the fact that they will not match in amp hours that will take it out? If that's the case then in theory my AGM I replace it with probably won't match the rear battery causing it to go bad again...? I'm assuming the time frame for that would be so drawn out that it wouldn't cause any issues...last post man and then I'll quit picking your brain. Thanks a ton again man!
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Old 10-22-2014, 04:26 AM
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I think the big thing with mixing AGM and FLA (flooded lead acid) batteries is that AGMs can be charged to a higher voltage per cell, where FLAs start gassing when the AGM is doing just fine. So if you charge to the AGM's full potential, you'll be gassing off the electrolyte of the FLA. If you only charge to the FLA's limit, you aren't charging the AGM to it's full potential. If it were me, I would replace the front battery with an AGM before doing anything else, as well as making sure your ground path is adequate between engine and amp.

I personally feel that having adequate alternator output is more important than having lots of batteries, because if you have plenty of alternator output, you'll never get down to battery resting voltage anyways.

If you want to see how well your stock alternator wire is holding up, you can put a multimeter on it and measure voltage across the wire. Put the - probe on the + terminal of the battery, and the + probe on the alternator's charging stud and play a tone at full tilt and see what voltage it reads across the wire. Ideally it'll read 0 volts, the worse off the wire is the more voltage you'll see across the wire. If you're seeing 0.5 volt drop across the wire, and are pulling 100 amps of current, the wire will be dissipating 50 watts of heat, with a resistance of 0.005 ohm. If you're dropping 1 volt with 100 amps of current, that would be 100 watts of heat dissipated with 0.01 ohms of resistance. You can do the same to see how well the ground is, put the - probe on the engine and the + on the negative battery terminal and see what you have for voltage, and do the same between block and body, or even use a piece of wire to connect the probe and the amp's - input and compare the drop there. I really can't say what's acceptable or not, but you can tell where the weakest link is as far as wiring goes. Whichever point has the highest voltage across it is the weakest link.

I know that in my suburban while I was still using a body ground, grounding was my weakest link before I added a few pieces of 2 gauge. I was seeing over 2 volts between the alternator case and the body, which affected my lights dimming quite a bit as well as the voltage present at the amp.

And go ahead and keep picking our brains, get all the info and knowledge you can, to get the best setup you can for your dollar. We like helping people get loud, and hopefully not kill anything in the process. I'm sure some of us have differing opinions and view points, Which I think it's great having varying opinions to consider when making decisions about your system. I know I like the approach of testing and figuring out what your weakest link is and continually reinforcing those weak links as you can without throwing money around if you don't have to.

Just curious, what vehicle / alternator do you have? Also what does the voltage sit at running with no load? I know you said it was a 150 amp alt, just wondering if that could be improved upon more cost effectively than adding batteries.

And I apologize for my long and somewhat rambling post
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Old 10-22-2014, 04:54 AM
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Dude keep rambling! I'm trying to soak it up..lol. i have an 05 Trailblazer with the stock 150 amp alternator. Resting voltage is usually 14.5-14.7. I do ground to the body with a short run of 1/0. No more than 3ft I would say. I currently have everything pulled out because I wasn't happy with the way I had things done, was moderately clean looking but I am upgrading all my wiring with sky high 1/0 and picking things up piece by piece as my budget allows. When I jumped back into car audio this go round I made the stupid mistake of settling for what I could afford at the time instead of making educated decisions.

I get what you're saying about alternator upgrade making the need to add batteries less apparent if you can just keep the one or two stay where they should. That being said I don't intend to go any bigger than what I am now because I still use it as my grocery getter. So for my purposes, swapping the under hood to an AGM and adding another in the rear should suit my needs.

It is definitely a work in progress though, have to work a little at a time with the budget.
While we're on the topic...opinions on batteries? I see every brand used just as much as the other probably but pros/cons in your expert opinions? Keep in mind cost effectiveness is a big help but want to make sure it's done right.
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Old 10-22-2014, 05:27 AM
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"I know you said my under hood battery will go bad at some point but is it "bad" to just keep a regular auto battery under there paired with the rear AGM?"

Not really. It will keep doing it's job, and that's to provide transient energy to they system when the alternator can't keep up. The problem is that regular wet cells aren't meant to provide a large amount of current for extended amounts of time and the recharge quickly from the alternator. The way the electrolyte and plates are designed will eventually cause failure over time; it might be a slow progression or a sudden failure, but it will probably happen. In my experience my charging voltage went up and voltage under load was better at the rear amps with my wet-cell battery removed and the single 93AH AGM in the back vs/ both connected in parallel - even with a wet-cell up front that was perfectly capable of starting and operating the car. It was acting as a leach on the system under load and didn't help anything. I actually don't have a battery under the hood anymore, and don't plan to add one back.


"Or is it the fact that they will not match in amp hours that will take it out? If that's the case then in theory my AGM I replace it with probably won't match the rear battery causing it to go bad again...?"

AH doesn't really matter, although the design of smaller AH batteries can bring their own limitations (smaller batteries typically have smaller terminals and different discharge and charge characteristics). AH is additive among multiple batteries of the same voltage in parallel, so if you have a single 50AH battery resting at 12.8v, and another at 100AH resting at 12.8v, you have a total 12.8v system with 150AH of capability. The problem comes when mixing a battery that's really good at releasing and then soaking up a lot of current at once (AGM) and a battery that's not (wet-cell). This can even happen between batteries that are the same but built at different times, so adding a brand new AGM to a system with another AGM that's 3 years old can cause issues because the batteries won't be charging and discharging at the same rates. If possible it's always best to have multiple batteries that are of the same chemistry and design and in the same relative condition.


"I'm assuming the time frame for that would be so drawn out that it wouldn't cause any issues...last post man and then I'll quit picking your brain. Thanks a ton again man!"

Yeah, it won't be an immediate thing. Lots of guys run mixed wet-cell and AGMs for years; I know I did. I could have kept going too, as there was nothing "wrong" when I removed my wet-cell. I rested at about 12.7-12.8v with the car off and dropped into the mid 12v range at idle on big transients. The car started fine every time. But then I removed the wet-cell and now I rest at 13v and my voltage drop is about .5v less than before, even though I technically have less reserve battery power. After a while of using only the single 93AH battery in the back, I added a small cheap-ish 24AH AGM in the front. That was almost a disaster, as 6 months later my voltage suddenly dropped into the high 11v range while driving and was sitting at 10.5v when stopped. As it turns out I'd dropped a cell in the new AGM and it was toast, but it was also bringing down the rest of the charging system with it. Loosing a cell means a 12v nominal battery turns into a 10v nominal battery, and that's no good. Anyway-the point is that getting a single good large AGM can save a lot of hassle in the future from having mix-matched electrical.

Enough of my rambling, lol. Here's a really good site explaining the differences and limitations of differing batteries, as well as what happens when batteries get older. Sections 804-806 are particularly important to what I described.

Battery Information Table of Contents, Basic to Advanced
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