Understanding battery ratings vs. playtime?

[STV_Keith]

OK, man, I'm more confused after all the reading that I was going in I think.
I guess what I'm trying to figure out is how to compare all these batteries.
Battery A: 75AHr (C/20?) rating with 155 minutes of reserve, 60#, sealed lead-acid
Battery B: 109AHr (C/20?) rating with 200 minutes of reserve, 69#, AGM
So, looking at these two, Battery A will put out 75amps for 155 minutes, but Battery B will put out 109amps for 200 minutes? What happens to the numbers, when you require 250 amps? 75amps x 155 mins / 250 amps = 46 mins or will that battery just not do it?
My head is starting to hurt.

[h2oski2fast]

1st off you have it all wrong. LOL
Reserve Capacity: The number of minutes a battery will hold voltage over 10.5v with a 25amp draw.
Amp Hours: How much amperage is available on a draw over a 20 hour period. For example: Your 109AHr battery will put out 109 amp total over a 20 period, or 5.45amps per hour for 20 hours (109AHr/20 hours = 5.45 amps per hour).
Hope this helps.

[STV_Keith]

1st off you have it all wrong. LOL
Well, I figured that was the case...thanks for pointing it out Dennis!
:crossx:
So, hell, the question is, what kind of playtime do you get from four Optima or equivalent Group 31's (battery A) with, say, a 5000 peak watt system? Figure 75 amps at any given time with bigger spikes for the bass?

[Havasu Hangin']

Well, I figured that was the case...thanks for pointing it out Dennis!
:crossx:
So, hell, the question is, what kind of playtime do you get from four Optima or equivalent Group 31's (battery A) with, say, a 5000 peak watt system? Figure 75 amps at any given time with bigger spikes for the bass?
The problem is that an audio system does not draw a constant load (like a golf cart for example). You can look at an average draw of a system at a given volume...but it will not be an exact science since you aren't playing test tones.

[h2oski2fast]

With a 75amp draw on the battery with 155 minutes reserve, you're looking at 51 minutes at 0 degrees celsius. That's what the math says, but the hotter temperature will have a big effect on the output of the battery. I'd say in all reallity you're looking at 30-40 minutes.

[Jordy]

When I had the 3 blue top Optimas in the boat, the stereo would run for about 4 hours at an obnoxious volume before it would start to cut out due to voltage drop and I'm not running 5,000 watts or anything terribly out of control. With the Trojans I found out on Saturday that I'm good for about 3 days before it will start dropping the sub amp because of voltage drop. Just something to think about. ;)

[STV_Keith]

OK, so next question since Jordy brought up Trojans (the batteries, right?).
So, 2 x T-105 (225 reserve @ 6v) trojan 6v's wired for 12v = 225 mins reserve at 12v right?
If that's the case, they will only offer marginally more time than a single 12v battery with 200 minutes reserve, correct?

[Tom Brown]

Keith, forget reserve capacity. It's pretty much meaningless to you. It will give you an idea of how the battery will last under a pretty heavy load but it doesn't play into your calculations.
A 100 Ah battery will put out 100 amps for 1 hour. ... or 50 amps for 2 hours... or 25 amps for four hours... and so on. At least, this is true more or less.
What really matters is watt hours. Unfortunately, it's not as simple as taking the Ah number and multiplying by voltage (as per Mr. Ohm P = I * V). The reason it's not that simple is the voltage will drop over time while the battery is under load.
If your amps cut out at 10 volts, you could pretend the average battery voltage is 11 volts and simply multiply that by Amp hours. It's not right and ignores a lot of factors but it's not terribly far off.
This way:
100 Ah battery at 11 volts average = 1100 Watt hours.
Let's say, you've got a 500 watts of Class AB power. Class AB will vary from 25~50% efficiency. Let's assume the amp is 40% efficient. That means your amps will draw 1250 watts when they're putting out 500 watts to the speakers.
At these levels, you could enjoy 500 watts of speaker driving electrical signal for a little less than an hour with your 100 Ah battery.
Am I the only one that thinks the 90ish % efficiency of Class D amps is well worth the money?
Let's see... 500 watts of Class D power will draw about 550 watts.and give you about two hours of play time on the same 1100 watt hour example battery.

[Jordy]

OK, so next question since Jordy brought up Trojans (the batteries, right?).
So, 2 x T-105 (225 reserve @ 6v) trojan 6v's wired for 12v = 225 mins reserve at 12v right?
If that's the case, they will only offer marginally more time than a single 12v battery with 200 minutes reserve, correct?
The way the guy at the battery place explained it to me was that with each of the blue top Optimas I had about 50 amp hours of use, so with 3 of them I was running 150 amp hours. Each one of the 6V Trojans was something like 250 amp hours, so with 2 I'm at 500 amp hours. Seems to work out that way on the water as I can run it all weekend without putting them on a charger where I had to hit the charger every night with the Optimas.

[Tom Brown]

The way the guy at the battery place explained it to me was that with each of the blue top Optimas I had about 50 amp hours of use, so with 3 of them I was running 150 amp hours. Each one of the 6V Trojans was something like 250 amp hours, so with 2 I'm at 500 amp hours. Seems to work out that way on the water as I can run it all weekend without putting them on a charger where I had to hit the charger every night with the Optimas.
The guy either lied or didn't explain it very well.
A pair of 250 Ah batteries in series produces 250 Ah of current. No more.
Of course, the voltage is doubled and so is the amount of power that the batteries can store and release.
... so the watt hours are doubled but the Amp hours stay the same.

[Havasu Hangin']

Seems to work out that way on the water as I can run it all weekend without putting them on a charger where I had to hit the charger every night with the Optimas.
Jordy...my two blue Tops lasted all day with 2,200 watts of A/B and D power on my old system. I'd say your Blue Tops either had issues...
...or you are blinded by all the acid in those Trojans.

[Jordy]

Jordy...my two blue Tops lasted all day with 2,200 watts of A/B and D power on my old system. I'd say your Blue Tops either had issues...
...or you are blinded by all the acid in those Trojans.
I'm just telling you based upon my dealings over the course of the last year, and the Optimas were brand new and are now being used as starting batteries in my boat. With the 3 optimas I had to charge them every day. With the Trojans I can go out all weekend, with more run time, without having to charge them every night. ;)
Besides, I wear my safety glasses when I uncork the Trojans. Safety first around this joint!!! :D :D :D

[Tom Brown]

With the Trojans I can go out all weekend, with more run time, without having to charge them every night. ;)
You should still charge them when you can. They'll last longer. Batteries that aren't fully charged accumulate sulfate on the plates that reduces their storage capacity over time. Of course, if the batteries are cheap enough, you don't have to worry about it a lot.
Here is my battery comparison (http://www.***boat.com/forums/showthread.php?t=118080) chart that is sure to piss everyone off. :D

[Tom Brown]

If your day was 6 hours, that's about 25 amps per hour. That's about 300 watts, give or take.
Not at all, Mr. Math.
25 amps at 11 volts is 275 Watts. If his amplifiers are 90% efficient (assuming most of the load is being handled by class D amps), that has him putting out about 245 Watts. ... and that's being generous.

[Tom Brown]

To produce 2200 watts, you'd need roughly 180 amps of current draw, which would deplete two fully charged Optima Blue tops in less than one hour.
To produce 2200 Watts with Class D power would require aprox. 2450 Watts. Again, at 11 volts that would be over 220 amps.
Try to get it right.

[Tom Brown]

Who runs at 11 volts? My volt meter never dropped below 12.7 this weekend. It's located about 2' from my amps.
Anyone who is away from an outlet all day. Fix your volt meter.
At 12 volts, that would be just over 200 amps.
Any battery will sag with time. If we assume the amps will start cutting out at 10 volts, and also a voltage sag under load, it's not unreasonable to assume an 11 volt average voltage through a discharge cycle. It's far from scientific, though.

[Havasu Hangin']

It's math. Your blue tops lasted because you're not putting any stress on your system, period. Let's say you have two D31Ms, each having a 75 aH capacity, for a total of 150 aH. That's all the amp capacity you have, regardless of what you think or how special you believe your batteries to be. Your batteries do not have the ability to suspend the principles of math or electricity. Let's say your "all day" is 8 hours. That means you drew less than 20 amps per hour. If your day was 6 hours, that's about 25 amps per hour. That's about 300 watts, give or take.
To produce 2200 watts, you'd need roughly 180 amps of current draw, which would deplete two fully charged Optima Blue tops in less than one hour.
I'm telling you guys, 8D submarine batteries are the only way to go, as Shadow has told you many times, and I'm telling you now. Another weekend of 12 hours of playtime over two days with no recharge at night. At the volume I leave the stereo at, I average between 40-60 amps current draw continuous, with peaks up into the 80s. A couple songs we'll kill it and start topping it out at 120-130 amps. Our stereo was on this weekend from the minute we set the first slide anchor until the minute we pulled out from the sandbar.
Ever wonder why the high-end audio 12 volts have lower internal resistance? Because your current needs in audio are dynamic. The more resistance you have in the system (wire, heat, etc.), the less current will be drawn...
...but performance will also suffer, which is why the pros don't use them.

[Tom Brown]

I guess my onboard volt meter, the voltage displays on all four Kicker digital amps, the voltage display on my SXRC and my brand new $400 Fluke meter are all incorrect, by exactly the same amount coincidentally. ;)
Bob... the energy in batteries is consumed over time. No battery can last forever. Not even your super duper best batteries ever.
Once again... for those who can't follow... if amps cut out at 10 volts... it's reasonable to assume an average discharge voltage of 11 volts through the discharge cycle.

[Tom Brown]

Ever wonder why the high-end audio 12 volts have lower internal resistance? Because your current needs in audio are dynamic. The more resistance you have in the system (wire, heat, etc.), the less current will be drawn...
A properly designed amp will have enough power supply head room, in the form of capacitance, to deal with dynamic loads. Better amps typically have more dynamic headroom.
If amps didn't have caps, you could use an external cap to increase the slew rate of the power source and smooth the load on the batteries. Properly designed amps don't need it, though.

[Havasu Hangin']

A properly designed amp will have enough power supply head room, in the form of capacitance, to deal with dynamic loads. Better amps typically have more dynamic headroom.
If amps didn't have caps, you could use an external cap to increase the slew rate of the power source and smooth the load on the batteries. Properly designed amps don't need it, though.
I've never had good luck with 6 volts on any high-end system (db meter and my ear). the only thing that sounded worse than using 6 volts...
...was using Kicker with 6 volts.

[Tom Brown]

I've never had good luck with 6 volts on any high-end system (db meter and my ear). the only thing that sounded worse than using 6 volts...
...was using Kicker with 6 volts.
:D
I hessitate to admit this.... but my boat came with Sparkomatic 6x9s. I took them out and put them in a box in the garage several years ago. Recently, I renovated the shop and had all the walls apart to improve the insulation, etc. Anyway, in all the hubub, I had these speakers sitting on the bench thinking I could give them to someone... preferably anonymously. :D
.... but some buddies came over and now I'm the king of Sparkomatic. :rollside:

[Havasu Hangin']

You ain't hurting my feelings, I don't have any Kicker speakers in my boat. My boat is loud and clean all the way up the volume control. From the amount of compliments and interest it receives every day we're out there, I'd say I did alright. ;)
Come on! You can do better than that?
I was waiting for the "You suck...you don't know what you are talking about...and I'm gonna come over and rape you dog for having a diferent opinion than mine"...
...standard ShockwaveBob response.

[Tom Brown]

...standard ShockwaveBob response.
Did you know he is an ex-marine?

[Havasu Hangin']

Did you know he is an ex-marine?
So was Lee Harvey Oswald.

[Tom Brown]

So was Lee Harvey Oswald.
No wonder the guy was so irrational. :idea:

[Havasu Hangin']

No wonder the guy was so irrational. :idea:
I wonder if Oswald ever raped a dog in his early days? :idea:

[Tom Brown]

I wonder if Oswald ever raped a dog in his early days? :idea:
... and if so, did he poke a bitch in the snatch, or did he go rectal on the dog. :idea:
Only a Marine makes those shots. Oh, and Marine is capitalized.
Actually, I wouldn't dump on military service. I live in a country where we don't love our military... to say the least. I have a lot of respect for military people, though. A lot of good people do a lot of good work for everybody. :)
I have a little less respect for throwing around being an ex-Marine in a heated discussion, though. I mean... for a while there you were whipping it out like it was the only lighter in a crack house.

[Havasu Hangin']

I live in a country where we don't love our military... to say the least.
But isn't it illegal in Canada to be on the internet while the Stanley Cup Finals are on? :idea:

[Tom Brown]

My posting style has evolved, as has yours I've noticed. You have probably mentioned that I was an ex-Marine more than I have. ;)
We all go through different things during different periods of our lives. I was a stay at home dad for almost 7 years. Although I love my kids and they are basically every minute when I'm not at work, I was a little unhappy/depressed by the boredom and lack of social interaction with other adults. Going back to work has really helped me get recentered.
It's all cool, Bob. I hope you understand, however, that I am required to bust you up. I'm not sure why and it really doesn't matter.... but I have to do it. :D

[Tom Brown]

But isn't it illegal in Canada to be on the internet while the Stanley Cup Finals are on? :idea:
There are definitely some people who, if they were to find out, would improve my morale substantially.

[STV_Keith]

OK, I'm still trying to get my mind around this. From post #2 up there, am I to understand that if two batteries have the same Ahr rating, but one has more reserve capacity, that the one with more reserve capacity will play longer?
I would think that's true. For instance, two 100Ahr batteries in parallel should have 2 x the reserve capacity of just one, right?
So, assuming the load (stereo) is the same, are you looking for the most reserve capacity in a battery with a similar Ahr rating?
IE: For sake of argument, 25A continuous load from the stereo.
Battery setup 1 has 4 - 12v, 110Ahr, 200 reserve min batteries wired in parallel. That system should have 440Ahr and 800 reserve minutes at 25A.
Battery setup 2 has 2 - 6v, 220Ahr, 480 reserve min batteries wired in series. So this setup should also have 220Ahr and 960 reserve minutes at 25A.
So which setup will play longer? The one with more reserve or the one with more Ahr?

[STV_Keith]

Sorry Jon, I was still editing when you posted. So it comes down to the reserve capacity?

[STV_Keith]

OK then, so 4 12v batteries with 110Ahr, 200 mins reserve will perform the same and have the same playtime as 4 6v batteries with 220Ahr, 400 mins reserve?

[STV_Keith]

Great! Now I'm getting somewhere.
Jon, what are your thoughts on this battery? It will fit in my application, and has very good specs from what I have seen. Thoughts?
http://www.power-sonic.com/pg-12v150.pdf

[STV_Keith]

Jon, have you ever heard of power-sonic?

[STV_Keith]

I did call and talk to them. They said they should perform well. I asked about cycling, and they said 200 - 1000 cycles from full to less than 10.25v, vibration will be no problem. They are an AGM sealed battery. 2 year warranty on them, pretty much no questions asked as long as they don't show signs of "abuse".
Also, cost wise, they are on the internet for $219 each, so very similar in price to the group 31's I've been looking at. They are a little longer at 19 inches, but I have room for 2 on each side. Should provide way more jam though, being 166Ahr vs 95-110Ahr for the standard G31's I've seen.

[BOBALOO]

I did call and talk to them. They said they should perform well. I asked about cycling, and they said 200 - 1000 cycles from full to less than 10.25v, vibration will be no problem. They are an AGM sealed battery. 2 year warranty on them, pretty much no questions asked as long as they don't show signs of "abuse".
Also, cost wise, they are on the internet for $219 each, so very similar in price to the group 31's I've been looking at. They are a little longer at 19 inches, but I have room for 2 on each side. Should provide way more jam though, being 166Ahr vs 95-110Ahr for the standard G31's I've seen.
I have 1 of these in my boat, well not the exact manufacturer, but it is a telecom batt and weighs 115lbs. I got it for FREE! Some of the guys at work use them in their Weekend Warriors. I rarely need it but when the 2 6V finally die after hours and hours it never lets me down. but by the time i need it it is already late in the night.
I say you get a quarter out of your pocket and call it in the air.:D I can say that my 2 Interstate group 27 batts only lasted about 2 1/2 hrs before the voltage got too low for the sub amp.