Which batteries are best for audio power??

[chpthril]

I thought that the amp rating, 40 or 20, was the max rating and that as the battery becomes charged, the rate steps down or "trickles". I will call Xantrex and get their opinion also.

Your right on there, you just have to watch the max volts as well. Amps to a battery is like GPH is to a ballist sack. The more amps, the faster the battery "fills up" but it can shorten the battery life over time depending on the amp output of the charger and the Ah of the batteries. Like Spharis said, a slow chargeis better over the life of the battery, just takes a little longer to reach full charge.

[TigeDuner]

How does a 20 or 40 amp charge compare to the charge from a 70 amp alternator?

[chpthril]

How does a 20 or 40 amp charge compare to the charge from a 70 amp alternator?

The alt will put out up to 70 amps to meet the electrical load (demand) of the accessories, as well as keep the batteries topped off, by means of a Regulator, much the same way the charger will.

[Coach]

The alt will put out up to 70 amps to meet the electrical load (demand) of the accessories, as well as keep the batteries topped off, by means of a Regulator, much the same way the charger will.

Remember that in most cases your stereo will be putting out a good amount of power and it will help bring the batteries back up some, but will not charge them up esp if you have been beached with the motor off and playing tunes all day. Alternators throw a big bulk charge at the bank of batteries.

[spharis]

It's like having an variable speed automatic bilge. The more GPH the faster it will pump when the bilge is full, but as the level of water rises, the output trickles down until it turns off. A higher GPH will empty the bilge faster when it is full of water, but it will do so at a greater power draw on the battery. Less GPH in the bilge pump will empy slower, but you will have less current draw. I don't know how that works as an analogy.

[Domsz06]

thanks for that info. That's great to learn it!

[Tanner]

To answer a few questions,

Well I mentioned that I didn't use the charger once this summer... that was because I get the T-105's until Labor Day weekend. However I ran the 4 T-105's all labor day weekend, and two additional weekends after that. I charged after the weekend after labor day. I put them on that night at about 8 p.m. and was back up fully charged when I checked on them at 11 the next day. I actually had the LARGE floor buffer Trojan Batteries at one point... I think the L16P's. They were sitting in my garage waiting for me to find a way to get those suckers in. At 100+ lbs a whack, they aren't easy to manuever. I took them back after a fella at Wake World persuaded me to run the T-105's.

As for the T105's and the heat... dom, sorry, I didn't really get to test it. It only hit low 90's at tenkiller this labor day. I didn't have a problem on the 100+ degree days at dirty bird after that though. My wholesale rep told me I really only need to check the water levels about every six months if your using a good charger. A smart charger will keep you from boiling the water off.

Two things I thought I should mention:

1. When looking at batteries, one rating that is of particular interest (at least to me) ... is the capacity minutes at a 75 amp draw. You can look at AH all day long, but they don't always tell you how that battery handles a large pull. There are a few batteries that have their AH's rated way up there, but when you look at their capacity minutes when they have a large draw... they aren't all their cracked up to be. Personally to me.... that rating is probably the most informative to the situation we are using. Most the major manuf. show it. Some however only show the cap. @ a 20-25 amp draw.

2. Remember that although your math may show you have a LARGE amp draw; even using your RMS ratings of your amp. Take that number and cut it in half. That's the average number that your amps are drawing. ON AVERAGE.... keep that in mind. You will hit spikes, and of course alot depends on your music. Rap will obviously draw more amps since it working your sub pretty hard. So while it may not seem like you have enough juice, you probably have more than you think.

[Domsz06]

I just know using 6 ppi amps they willl draw a lot of power, plus running a cooling system to keep them cool, so I know I'll need the power

[TigeDuner]

Dom, sounds like you need a diesel generator to power your system.

[Jeff T]

Two things I thought I should mention:

1. When looking at batteries, one rating that is of particular interest (at least to me) ... is the capacity minutes at a 75 amp draw. You can look at AH all day long, but they don't always tell you how that battery handles a large pull. There are a few batteries that have their AH's rated way up there, but when you look at their capacity minutes when they have a large draw... they aren't all their cracked up to be. Personally to me.... that rating is probably the most informative to the situation we are using. Most the major manuf. show it. Some however only show the cap. @ a 20-25 amp draw.

I have been pricing out wet cell batteries. I'm not looking to spend a lot...I just want to have needs met.

Today, I went to Sportsman's Outfitters. They sell Trojan batteries. I looked a the deep cycle SCS225 @ $129. It had the following specs:
-130 AH @ 20 HR
-105 AH @ 5 HR
I don't understand the ...@ x HR. What does that mean? Why is it lower @5hr than 20hr?
-225 min @25 amps
-57 min @ 75 amps
What is would be considered good at a 75 amp draw? After looking at Wal-Mart, Autozone, and Advanced Auto, I have yet to see a deep cycle w/ the min @ x amp rating.

For reference, using the formulas that have been posted several different times, I calculated that my system will require 144 amp hours (40% x 8hrs). I know that I won't need 144 amp hours because I know that I will NEVER run my system 8 straight hours without moving the boat (I also have a beefy, 140amp alt that will give me a good charge). The X minutes @ X amps rating just confuses me even more.

[Coach]

I have been pricing out wet cell batteries. I'm not looking to spend a lot...I just want to have needs met.

Today, I went to Sportsman's Outfitters. They sell Trojan batteries. I looked a the deep cycle SCS225 @ $129. It had the following specs:
-130 AH @ 20 HR
-105 AH @ 5 HR
I don't understand the ...@ x HR. What does that mean? Why is it lower @5hr than 20hr?
-225 min @25 amps
-57 min @ 75 amps
What is would be considered good at a 75 amp draw? After looking at Wal-Mart, Autozone, and Advanced Auto, I have yet to see a deep cycle w/ the min @ x amp rating.

For reference, using the formulas that have been posted several different times, I calculated that my system will require 144 amp hours (40% x 8hrs). I know that I won't need 144 amp hours because I know that I will NEVER run my system 8 straight hours without moving the boat (I also have a beefy, 140amp alt that will give me a good charge). The X minutes @ X amps rating just confuses me even more.

The number I look at is the 20Hr number. As for the Trojan SCS225 is that a 12V? my guess it is. For your system one should be enough. If you need more power you can always add another.

[Tanner]

The reason it is lower at 5 hours vs. 20 hours is because your putting more of a draw on the batter. To translate what that means.... that is the amount of amp hours you are putting out if you drain the battery down in X amount of hours. A good analogy would be like your MPG in your car. If you held a constant 65 mph your gonna get better gas mileage and your gas tank is gonna last longer than if you have your foot buried in the gas the whole time.

You can compare two batteries by looking at the 20Hr rating. The reason I use the capacity minutes at a 75amp draw is because it tells you how much playing time your going to actually get.... relatively speaking of course.

I pretty much stick with trojans because of their rep. BUT supposedly, almost all batteries are made by one large manuf. for everyonce else. That's why you'll notice their casings are similar. If I'm informed correctly the manuf. is trojan. So in other words, those costco and wal-mart batteries are trojans. Now I don't know how true that is, so don't quote me on it.

If it is true, I know there's got to be some corners cut somewhere. It's like Home Depot, Lowes, Wal-Mart etc. They cut costs by using cheaper materials. For instance ... in my business (I build custom houses in the luxury to ultra luxury market)... plumbing fixtures at a plumbing supplier (I.E. Ferguson plumbing) can also be found at lowes. The fixtures will look identical. The difference is, the guts of the lowes/home depot fixture will be all plastic instead of brass and copper. The warranty won't be as long either. Same goes for light fixtures, at a lighting store vs. the above mentioned discount stores.

I'm not trying to make decisions hard, just saying, usually you do get what you pay for.

[Jeff T]

That makes perfect sense. So, is 57 minutes @ 75 amps a good rating, a middle of the road rating, or a low end/don't waste your money rating?

What exactly is an AH? I know how to get to the calculation, but I'm not exactly sure what it is telling me. I get the xAH@x hours. That makes sense now that you explained it. But I really don't know what the actual AH is.

Also, let me make sure I've got this right. If my system is consitently pulling 75 amps, I will run out of battery (assuming it is fully charged) in 57 minutes?

Here are my specs (based on (sqrt (rms/ohm)):
Amp 1: Kicker zx750.1
-750watts RMS @ 2ohm ~ 19.4A

Amp 2: Kicker zx 650.4 bridged
-325 RMS @ 2 ohm (mono). I will back down significantly: ~ 9A (assuming I don't back down)

Amp 3 Kicker 350.4:
-60amps x 2 channels (60x2) @ 4ohm ~ 5.5A
-90amps x 2 channels (90x2) @ 2ohm ~ 9.5A

-Sum of all 43.4 or ~45. Lets just call it 50 for simplicity. If I run at 50% or 25 amps, I will get 225 minutes out of this battery. I'm I thinking about this correctly?

Thanks for all the clarification.

[Tanner]

Each device you use has it's own Amp's per hour rating. Every once in a while you'll find this rating on some electronic devices if you read the manual. An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH. The standard is the 20 hour rating. Now here's where things are sort of fishy and I'll spare you the detailed physics lesson. A phenomenon called the Peukert Effect (insert MPG analogy I used above) causes you to lose power the faster you drain the battery. So your probably gonna be using the 5AH rating instead of the 20AH rating as it's gonna be closer to how fast your draining your battery.

Are you still with me to this point?

Now the math you done is flawed. Amps = W / V

The key to remember here is that the ratings given from the manuf. are at 14.6V. Most fully charged batteries in a boat will give you somewhere around 13.2V. But 12.6 is kind of a magic # that is used with eletrical systems in the automotive environment. Because of this, your amp probably won't put out it's actual max rating. But we'll use the max #'s anyways, since they will give you some breathing room.

Kicker Zx750.1 (probably pushing above 900W but we'll say 800W)
800/12.6= ~64 Amps

Kicker ZX650.4
325/12.6= ~26

Kicker ZX350.4
I'm gonna say around 300W for #'s sake if you had it bridged into one channel
300/12.6= ~24

So around 114 Amp draw from your system. We'll take say 60% of that as what your really using ON AVERAGE.... so just under 70 amps.

So the 75 amp capacity is a very good number for you to use. Thus you'd have a little over an hour of play time with that battery. If you had two of these (assuming they are 12V's), you could wire them up to give you 2 hours of play time. Assuming your system doesn't ever draw from your alternator (which isn't true while your boat is running).

I hope I didn't lose you. Something to keep in mind, these ratings and numbers are in an ideal environment. Which we are not in. Most batteries in my experience will give you more power than they are rated at.

You asked about that rating being good or bad. For a 12V it's about average with some of the upper end batteries. Actually I think it's what the Optima Blue top gives out (I haven't checked those #'s in a long time, so don't crucify me if I'm wrong). 6V batteries tend to have larger capacities than 12V. That's just the manufacturers. The Trojan T-105 (6V) has a 115 min. capacity at a 75amp draw. That's one of the best around until you get into the monster batteries (size wise). I had a couple trojan's that had a 220 min cap. at 75 amps ... but they were HUGE. Couldn't really fit them anywhere and they were 100+ lbs a piece. The problem with 6V's in our scenario is you need two of them to make 12V.

So basically your left with a couple of options... 2 6V's to make one large 12V. 2 12V's to equal the capacity of the 6V's. Or get crazy like me and do 4 6V in addition to your starting battery and wire them into the isolator to keep the stereo seperate from your starting battery .

P.S. ... when your batteries start sparking... just remember ... it's decoration for your boat.... Just think of the fourth of the July ... lol...j/k.

[spharis]

The math he's done is for an average, not an exact. Keeing everything at 60% is for a rating factor. That is an electronic standard, no matter what you are figuring. You should keep everything to 60% or less of its rating.

The most accurate current draw per amp is going to come from the specs in the owners manual, but the math there is good to get a pretty close number. Using the reistance of the circuit is a better method. You have to use the native rating of the amp to get the proper load, if you are using the forula you have as it does not take into account the resistance internally on the amp.

In the case of the ZX750, it would be 375@ 12.6....so closer to a 29ishA power draw, or closer to what he has. But yeah there are a gabillion different ways to figure it. Reason being it is a little closer to use the channel output, is that unless there is a massive frequency, you will never see that max power draw on the circuit. Using the channel ratings will give a more realistic number to work with. I use the channel rating as the test I have done with multimeters, and scoping seems to reflect it as a more accurate number vs the voltage and overall output. I always scope and meter amps upon installation to be sure the levels are matched correctly.


**********below is quoted from somewhere****
The Amp Hour rating tells you how much amperage is available when discharged evenly over a 20 hour period. The amp hour rating is cumulative, so in order to know how many constant amps the battery will output for 20 hours, you have to divide the amp hour rating by 20. Example: If a battery has an amp hour rating of 75, dividing by 20 = 3.75. Such a battery can carry a 3.75 amp load for 20 hours before dropping to 10.5 volts. (10.5 volts is the fully discharged level, at which point the battery needs to be recharged.) A battery with an amp hour rating of 55 will carry a 2.75 amp load for 20 hours before dropping to 10.5 volts.