THE MOST UNUSUAL 12 volt system build question - AVS Forum
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post #1 of 5 Old 03-14-2012, 10:16 PM - Thread Starter
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Hi all,

This may possibly be the most unusual question/system build that you have come across...

I work in a automobile manufacturing plant and we are allowed to have radios/music systems as long as they are battery powered. Most of what I have seen there consist of a couple or more of 6x9 car speakers, a head unit and a deep cycle battery in a cabinet. I have to work with what I can get my hands on and have come up with a design that seems, to me, pretty good.

I have a 4 Energy e:xl 15 bookshelf speakers left over from an old home theater that I have gutted and removed the drivers and crossovers from, a Lanzar MNX250 2channel car stereo amp(http://www.lanzar.com/sku/MNX250/100...sfet-Amplifier) and 2 Lanzar MAX8 8" (http://www.lanzar.com/sku/MAX8/Max-8...-Ohm-Subwoofer) subs to work with. All hooked up to an MP3 player.

The Energy speakers are 8ohm and will be wired in parallel/series to present an 8ohm or possibly a 2ohm load to the amp. The amp is rated at 250W@4ohm/350W@2ohm and I am assuming 125W@8ohm.

All of this must be run from a single 12v deep cycle battery for as long as possible.

The biggest concerns for me are volume and run time. I need to get enough volume to overcome the ambient noise of a factory setting but at the same time, I don't want to haul my battery home every night to charge it.

I have a couple of questions:

1.) Which will be a larger drain on the battery, an 8ohm load or a 2ohm load? Or does it depend on volume?

2.) I can't find the specs on the amperage draw for the amp to know what sort of battery to buy. What is a safe bet to buy as far as a battery to run the system for at least a 10 hour shift, but a couple/few shifts being preferable?

Thanks in advance....
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post #2 of 5 Old 03-15-2012, 09:19 AM
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1) Depends on volume. The speaker load won't matter too much because it depends on the amplifier. A Class-D amp or Rockford Fosgate's BD amps would be the main focus for conserving power. They are far more efficient > 80% vs. < 60% for traditional amps.

2) An amp just like any electric device will draw power based on what it needs therefore it's amperage draw will vary with the music power demand and volume. If you do see an amperage draw rating on any device it is merely a maximum safe rating.

After you are done working, I'm assuming there is a way for you to recharge the batteries? Like an AC charger? Otherwise it might be a good idea to have two batteries. One that is charging while the other plays then swap between the two as needed. Then the party can be non-stop!
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post #3 of 5 Old 03-15-2012, 06:02 PM
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Did a bit of research on the components.

The energy speakers are a dipole design with a 5 1/4 woofer and 2 tweeters. I am betting the rear firing tweeter was wired out of phase. The speaker is an 8 ohm speaker.

The amp appears to be a tiny class D design. 50 watts per channel. DO NOT believe the specs they are giving out. It has a 30 amp fuse. It should be fairly efficient.

Get an AGM battery. Sams Club sells an energizer or duracell brand made by Deka (a great battery manny). Find a cheap automotive battery charger so that when you have access to a wall outlet. I did something simiar for my toolbox to accomodate a power strip for a small boombox, drill battery charger and cell phone charger.

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post #4 of 5 Old 03-25-2012, 07:26 AM
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You are not even allowed to plug in a boombox?


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post #5 of 5 Old 03-26-2012, 05:14 PM - Thread Starter
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Sorry, I've been working a lot lately.

I got it built and it works great and sounds awesome. Blows everyone else's out of the water. The e:xl15s are the ones with the single tweeter and 5 1/4" woofer. Techronics sent me a Lanzar htg237 instead of the mnx250 I ordered. Oh well, i'm using it anyway. I wired all 4 of the e:xls to one channel to present a 2ohm load and the max8s to the other channel, also at 2 ohms.

After a week of listening for 9-10 hours a day, the deep cycle battery lasted me around 35 hours. I did not try to conserve power and listened at whatever volume I pleased.

All this week, i've also been digging around and found out a few new things. Driving an 8ohm load does indeed draw less current from the battery although the power drops. As impedence gets lower, efficiency drops as well. Also, as razel stated, class d amps are more efficient and will drain my battery slower.

That being said, I think I'm going to start looking for a new amp. The Fosgate r400-4d is looking good to me right now. 2 of the e:xls wired in parralel to present a 4ohm load on each of 2 channels and the 2 8"s on the other two channels @ 4 ohms each.

We have to take our batteries home to charge and it's about a 1/2 mile walk through the plant to my car. Id like to get around 50 hours or so out of one battery so i would only have to take it home once a week.
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