How to calculate battery life with a big stereo?

[Julian]

Anyone got a good link to a calculator that will tell me how long a battery would last when connected to a big stereo? My 242x currently has 1000w of amps and I'm about to add another 500w amp (cuz I have a wetsounds amp laying around and bought a pair of JL speakers from a member here). Just curious how long this would last as various volume levels....if there is any way to calculate it!?

 

[veedubtek]

I'm no electrical engineer. But, if it were me and I wanted to calculate that, I'd be using an amp-clamp to measure what it's actually pulling, and then looking at the amp-hour rating of the battery. You'd really need to take an average reading with the clamp over a short period of time and do the math with that number. If you're really interested in pursuing this, I could bring an amp clamp to falls this weekend? I'm planning on likely heading that way.

 

[KXCam22]

Veedubtek has the right idea. You can't really calculate it without doing a couple of tests. Amps are notorious for advertising a power rating but drawing a current from the battery that does not correlate to the amp power. Best thing is to:

1. Measure the current flowing to the amps and head unit for each volume level you want data at. Best place to do this is at the main + battery lead - then you get it all. You will need a DC clip on amp meter.
2. The batteries will have an amp-hour rating. Simple math will divide the amp-hour/amps to give you hours of run time. Subtract about 20% time to account for decreasing battery voltage as the amps will start to shut down when the voltage gets too low.

That is a simplistic way but will work. Others may have more exact methods. Cam.

 

[Bruce]

You do not want to discharge the batteries below 50%. So that is a big factor in your calculations.

Different types of music will use differing amounts of power through the same equipment. The most power will be consumed during the bassiest parts of the song. So listening to rap will run your batteries down faster than metal.

1,500 watts is 115 amps at 13 volts. I would guess that your average draw would likely be around 1/3rd of that or 55 amps if you are operating at full volume playing music with lots of base. On that basis you would need a large 100 Ah battery for every hour you planned to play music. But I doubt you really listen to your music that loud. This would be playing for the cove overpowering other boats volume levels.

A simple way to test would be to charge your house battery, play the stereo for 10 minutes, check the voltage then play the stereo for thirty minutes and check the voltage again. Those voltage readings can be used to approximately calculate the percentage o the battery used. There is a decent state of charge chart at http://modernsurvivalblog.com/alternative-energy/battery-state-of-charge-chart/ . I believe this will give you a more accurate estimate than using an amp clamp as consumption varies greatly as the music does.

If you want to run for a long time on the water you should consider golf cart batteries for their low cost and and high storage capacity. I have used them for years for tower and server battery backup.

 

[David Analog]

It's a hopelessly complex calculation and there is no accurate calculator.
Music is AC in nature so the draw is only a fraction of the DC calculation.
Amplifier efficiency will differ based on the Class and the impedance load channel by channel.
The circumstantial fluctuations can go on and on.
For certain, you know that 12.0 volts (50% charge level) is the lowest permissible discharge level for reasonable battery longevity. So upon your first outing with typical habits, measure the battery voltage after a long period at rest. This will tell you if you can stand pat or you need to add on capacity.

 

[Julian]

Thanks for the replies....good info!

One more question....I am installing a 4 channel Wet Sounds HT4 amp and will likely use it to power a pair of JL MX650s. Any special way I should connect this to the speakers? I was planning on setting the high pass filter (since the boat has a sub). Other than that...any other thoughts?

I've asked for the speaker wiring diagram as the tech at Chatlee Marine mentioned that two of the speaker pairs in the boat were wired inline. If that is the case, I assumed it would make sense to move one of these pairs over to the other channel of the wetsounds amp to reduce the load on the polk amp....

 

[Firehouse100]

You may want to add a digital fuse block. You can estimate your drain by looking at the the draw. For example if your battery is rated at say 200 min rc at a 20 amp draw and you are drawing 20 amps then that battery would run just over 3 hrs. Also in general deep cycle batteries are considered dead at 10.5 volts so if you have a way to check your voltage say with a chart plotter and your battery was fully charged at 12.9 then 11.7 would be 50%. Also deep cycle batteries are designed for a heavy drain and will last for years if you fully recharge them after each use.

 

[MattFX4]

good question. Do you have any issues running 1,000 watts? I currently have 800 watts of JL audio class D amps and have no problems with battery drainage from the two factory interstate batteries. I am about to add a wet sounds syn-dx4 amp so I will be doubling my wattage to 1,600. I think I may upgrade to larger batteries next spring for more juice.

 

[Mainah]

@Julian - You should be just fine. That wetsounds amp is a lot better than those polk amps and will be efficient. I would definately split the swim deck from rear cabin. They were in series on my boat but check yours as it could be different given the stock amp setup.

@MattFX4 - You should be fine as well.

For both you will get longer run times out of a pair of group 31 agms but can make the decision if you need to do that after installing the new gear. Might be a very good idea to do the connext voltage fix so you can monitor while floating.

 

[Firehouse100]

Just curious, why do like the wet sound better than the polk? I am running two of the Polk pad4000.4 the specs are comparable to the wet sounds. I think I run the filter in the off position on the regular speakers and the sub amp at the low Pass. I think my reasoning was your regular speakers can fill in some mids that may be excluded by filtering. I quess to me it just sounds fuller and I can adjust the eq on the head unit because I don't think I'm getting an eq at any time in the future.

http://www.sonicelectronix.com/lp/pla-4-channel-amplifiers/pad40004?utm_source=google&utm_medium=cpc&utm_campaign=PLA&affiliate=googpla&scid=scplp3610917&sc_intid=39894&adtype=pla&lsft=adtype:pla&gclid=CJyQ5KPnvNACFUdahgodEzkIKQ

 

[Mainah]

I like JL amps the best. They are very efficient (probally the most effecient for power drawn vs. output in the market) have rollback technology, exceed extreme enviormental operating standards like no other and are accurately or underated rated for power output. There is a video with an inside look at their factory in Florida that shows the lengths they go to. Wetsounds would be number two for all of those things in my book for a marine class D amp.

IMO the rest under deliver on power output and are a bit less effecient. I had the chance to hear the stock setup in a 242x which uses polk amps. The gain on the sub channel was maxed out and would not do what bridged channels on a jl m400/4 would do at half gain for the same overall output watt rating.

Polk, Kicker, and JBL (rated in that order IMO) are certainly better than Boss audio and the like but the only thing that holds a candle to JL audio in marine amps is Wetsounds IMO.

I would recommend turning on the highpass filter for full range speakers and set it to around 60-100 Hz. depending on the speakers and provided you have a sub. You will be able to play the full ranges louder that way. If no sub then you may still want to turn on the highpass filter to its lowest setting as full ranges can't play as loud when TRYING to produce bass and at the same time produce mid and high frequencies. For subs the lowpass should be between 100 and 150 depending on the sub and the highpass setting for the full ranges. You want a bit of overlap. Tuning the gain with a multi meter also helps.

For reference when I built my system I did compromise on speakers (Polk) but did not and would not compromise on batteries, amps, or wire (group 31 agms, JL Audio, and knukoncepts).

Sorry for the long explanation.

 

[Mainah]

Found that JL audio video I mentioned.

 

[Firehouse100]

Good video. They are about a half hour drive from my house. Do you know what model amp they used in the 242 and what model polks did you install. I'm running 8 6x9 mm961's. I think the durability of both models are outstanding (speakers) JL is very popular around here, except for me I guess. I did have a friend that had a rusted tweeter on one of his sevens after two years though. I had a set of the older momo's on my tower that lasted over five years 24/7 in the direct sun and rain. The distortion was coming from a blow resistor in the crossover. Since the enclosure was off the boat I just replaced them all. Not to bright but I never covered them.I kept putting off getting a cover. Now the new ones are covered. Maybe I'll start messing with the amps to see what happens. Thanks for the recommendation.

 

[Mainah]

Not sure on the exact polk amps in a 242x. I have a mix of polk db 521, polk mm 651, mm 691, and mm 1040. I am happy with them but belive the JL models are a bit better. I have two jl 400/4 driving them and am impressed with the power output. Do think the gain is turned up past half for any of the channels. 4 pairs of 6x9 mm must sound pretty darn good and loud. If the amps aren't maxed out on the gain, clipping, or going into thermal shut down then I personally would not mess with it until something fails or you make other changes.

 

[Firehouse100]

Cool thanks, I think they are about a third on the gain, supposedly they are two ohm stable along with the speakers. I also have a third amp that powere 2 mm651 and a bridge to the sub. Outside of the clarion amp I'm all Polk, so every speaker has its own channel. I have had them shut down before but that was due to low voltage and pushing up the volume.