Stereo/Battery test day. How many hours will I get?

[drjames1107]

Ok so my Stereo is complete and as previously mentioned it sounds great!!! ( I have only tested for short periods maybe an hour or two) My question is Battery charge as we will be on the lake today for about 9 hours.

I have installed:

Wetsounds:
2 Rev 10's tower
6 XS-650 coaxial
1 HT AS 10 - 500 watt powered sub
Syn4 @ 800 watts
HT6 @ 660 watts

I have all this hooked up to 2 group 31 Optima Blue Tops in Parallel.

MY Question is How long can I play this today? We probably cruise 50% and sit 50% of the time. Anyone else have similar system have an estimate on how long battery will last?

 

[TechRider]

Volume and watt / amp consumption by the amplifiers is the only way to determine the draw and how long your batteries will last. If you are pushing those amplifiers at 500 watts combined that's going to be about 41 amps (watts / 12 volts = amps). I think the group 31 blue tops are rated at 105 amp hours. Volume is the key.

Remember when on cruise you are recharging as well so crank the tunes when cruising You should be fine with 2 group 31's. That's what I have.

Let us know how it does! Check the batteries using the volt meter on the dash when the engines are not running and see what voltage you have. Use the grid below to tell how depleted the battery is.

 

[txav8r]

Volume and watt / amp consumption by the amplifiers is the only way to determine the draw and how long your batteries will last. If you are pushing those amplifiers at 500 watts combined that's going to be about 41 amps (watts / 12 volts = amps). I think the group 31 blue tops are rated at 105 amp hours. Volume is the key.

Remember when on cruise you are recharging as well so crank the tunes when cruising You should be fine with 2 group 31's. That's what I have.

Let us know how it does! Check the batteries using the volt meter on the dash when the engines are not running and see what voltage you have. Use the grid below to tell how depleted the battery is.

Correct me if I am wrong...but our stator magneto charging systems produce only about 26 amps of charge at any given time...and if you are using 41 amps, you are still reducing battery state. Playing at max levels will reduce your batteries no matter whether you have a DVSR or ACR. You are offsetting the drain, but you are still draining the stereo bank. The more you cruise, the less direct drain you have but you still have a drain if your volume is causing a usage greater than the capability of the charging system. Chances are, you are not playing at max levels when at rest either, so those two group 31's will give you a great deal of time...but probably not 9 hours at rest, at a high level. I suspect you can get close to it however, if you are running at 60% to 70%...but I haven't done the math. The only way to truly define the limits is to find them! In the words of the band Wild Cherry..."Play that funky music"!...and find the edges of your envelope!

 

[David Analog]

500 watts will not come anywhere close to 41 amps of draw. This isn't a DC equation like a light bulb. Music is AC content. Then you have to consider the amplifier efficiency of Class D and H. Then there are countless other variables.
Make sure that the stereo bank gets serviced throughout the day by the boat's charging system until after a long duration at rest. An ACR will automatically take care of this. But you can also manage this via a manual switch if you can accurately read the bank's voltage.
You can safely reintroduce the boat's charging system to deeply depleted batteries if you temporarily shut the stereo down.
Here's the key....the ability to read the bank's voltage at important times. Don't speculate. Measure instead. You never want to drain a consumer grade deep cycle battery below 50% (12.0 volts) other than on the rare occasion. If your usage and habits deplete the bank farther then you need more capacity. A deep cycle battery will accept an inordinate high number of shallow cycles but an inordinate low number of deep cycles. Depth and quantity of cycles is not a linear ratio.

 

[maboat]

...You never want to drain a consumer grade deep cycle battery below 50% (12.0 volts) other than on the rare occasion. .... A deep cycle battery will accept an inordinate high number of shallow cycles but an inordinate low number of deep cycles

Interesting. Why do they call them "deep cycle" batteries?

 

[drjames1107]

Ok so we were only out for 6 hours today, it got too windy. But for the 6 hours I would say we were running about 60% of the time and sitting for 40%. While running (kids were tubbing) we had stereo at about 70% volume, very loud. While at rest we were listening at about 25% volume at most. I also inflated 2 large tubes from the accessory outlet which I believe goes to the house batteries also. Anyways I was still at 80% battery life, so I do believe the 2 Group 31's will be plenty of battery for my 1960 WATTS of stereo. Very Happy!

 

[David Analog]

Interesting. Why do they call them "deep cycle" batteries?

Cranking batteries won't tolerate deep cycles without degradation showing up relatively soon. Lots of plate surface area but not much plate thickness. Thus best for quick amperage delivery.
Consumer grade deep cycles give the best performance and longevity when you limit the discharge to 50%. Yes, having a 'deep cycle' label but could be considered more of a hybrid. And many boaters use a deep cycle or DP battery in their starting bank. These batteries also have to conform to acceptable consumer price points.
I would give golf cart batteries a bit more latitude in depth of discharge. It's a slower discharging battery made for more of a specific purpose. A ratio of thicker plates with less surface area.
There are commercial grade batteries that accept a repetitive 80% discharge and still maintain a long service life but those batteries would be considered cost prohibitive by most. And these ultra-expensive batteries may be too slow of a release for an audio related application.

 

[David Analog]

I might also add that running your audio electronics with a lower voltage supply isn't particularly healthy. Amplifiers operate less efficiently. Overall audio quality diminishes....bass begins to thin. Starters last longer with a strong voltage. Better for boat electronics too. Many alternator rebuilders would be put out of business if everyone used their batteries with the proper discipline and changed them when appropriate rather than trying to stretch their service.

 

[rickd01]

@David Analog , define cost prohibitive, monetarily speaking?

 

[TechRider]

@drjames1107 good news!

 

[David Analog]

[ QUOTE="rickd01, post: 17845, member: 224"]@David Analog , define cost prohibitive, monetarily speaking?[/QUOTE]

For example, let's say a 12 volt industrial grade fork lift battery rated for 80% depth of discharge with a 500 A/H capacity. Might be $1500+. I'm pretty sure that most wouldn't spend that. If they needed that type of A/H capacity they would be more likely to go with four 6 V consumer grade golf cart batteries at a fraction of that cost....not to mention the mobility.
So the real point is that any legit industrial battery that can consistently tolerate 80% DOD without a sharp decline in number of cycles will be expensive. And that consumer grade deep cycle batteries, despite the label, won't tolerate 80% DOD.