QuestionQUESTION: I was wondering if it is possible to install a battery in the back bed of my truck to run a small subwoofer setup and what I would have to do for the installation.
ANSWER: Hi Robbie,
Can you give me a little more detail on what you're trying to do? Are you planning to use a separate audio system in the truck bed sometimes while the engine is off, or is the subwoofer intended to work with the existing audio system in the truck? Do you plan to connect the battery to the truck's alternator and charging system, or will it be completely separate, and recharged with an external battery charger?
For most applications, you'd probably be better off just running power cables to the primary battery under the hood instead of adding a second battery in the truck bed. Additional batteries are seldom useful in typical "daily-driver" audio systems, but there are a few cases where they make sense.
Please follow up with more detail, and I'll see what I can do to help you.
Thanks
Brian
---------- FOLLOW-UP ----------
QUESTION: I just wanted to have two ten jl audio subwoofers with a kenwood 1000watt amp. it will work off the stereo in the truck. The reason why i was asking was because two years ago I lost all the power in my vehicle while driving. the vehicle had power steering and brakes, so i had no control of the vehicle and i was doing like 60mph and did not want it to happen again. The mechanic that fixed it said it was most likely because the subs& where drawing to much power. I was wondering what would have been needed for the installation of a battery in the back bed
AnswerRobbie,
I'll go ahead and answer the question you asked (what's needed for installation of the battery in the truck bed) before I address the issue of whether it's a good idea for your application.
For best results, you'll want to use a battery that's identical to the one under your hood. Marine-type battery boxes are available to enclose and protect the battery in the truck bed. In addition, you'll need a heavy-gauge wire to run between the positive terminal of the rear battery and the front battery. The minimum wire size I'd use here is 4-gauge, and it doesn't hurt to go bigger. The wire needs a fuse and fuse holder at each end, near the respective battery terminal--a single fuse at one end won't be adequate protection in case of a short circuit. For 4-gauge wire, you'll want to use a 100-amp or 120-amp fuse. This generally requires a MAXI or ANL type fuse and fuse holder.
You'll also need a shorter wire to connect the negative battery terminal to the vehicle's frame. This wire should be at least as thick as the wire on the positive terminal. It wouldn't hurt to upgrade the wire between the existing battery's negative terminal and the vehicle chassis as well.
You'll need battery terminals connectors to attach the wires to the new battery, and a ring terminals for the connection at the front battery and the ground point connection. If you're routing the wire under the truck body to get to the truck bed, don't forget some wire loom (or even flexible metal conduit) to protect the wire, as well as cable ties and cable clamps to secure it in place.
You can find dual battery isolator systems, based either on heavy diodes or an ignition-powered solenoid, but for your purposes you probably wouldn't need an isolator. A battery isolator allows you to run various accessories from a secondary battery without draining the primary battery. They let you play your audio system for long periods without the engine running, and still be able to start the engine later from the primary battery. (If you plan to do this, you'll want to use a deep-cycle battery in the rear, instead of one that's identical to the front battery). Since it sounds like you'll primarily be using the system while driving, you don't need to isolate the batteries.
Now that I've told you what you need for this project, I'd recommend that you don't do it at all.
I don't agree with your mechanic in this case: I've never heard of an issue like yours caused by an amplifier and subwoofer installation, provided it was properly connected directly to the battery terminal, not to some other part of the vehicle's electrical system.
It's true that a high-powered car audio system can overload and shorten the life of the vehicle's alternator. When an alternator fails, however, it doesn't typically result in an instant, catastrophic loss of power. It basically just places the vehicle's electrical load back on the battery, which slowly drains until it can't sustain the vehicle systems any more. During this time, you should at least get a dash warning light, dimming lights, slower-blinking signals and other indicators of trouble before the engine finally shuts down. (Of course, if you don't notice the trouble signs, the engine shutdown while driving can come as a rude surprise).
Here's the main problem with your plan, though: adding a second battery does not reduce the strain on the vehicle's charging system. It actually results in an increased load on the alternator.
You have to understand that while the engine is running, the alternator is the primary source of electrical power in your vehicle. The primary battery, and any secondary batteries, do not produce power when the alternator is operating. In fact, they consume power, because one of the alternator's jobs is to keep the batteries charged. Because there's always some internal resistance in a battery, even a fully-charged battery will always be using some current from the alternator's output. A partially depleted battery uses much more current as it recharges.
The only time the battery produces power, instead of consuming power, is when the alternator isn't maintaining a charging voltage: either the engine is off, the alternator isn't working, or a short-term current demand has temporarily overloaded the alternator's output capacity, resulting in a voltage drop. A working alternator typically produces around 14.4 volts; until the voltage reaches the battery's standby voltage of 12.6 volts, the battery will be consuming power, not producing it.
To sum up, if your intention is to reduce the load on your truck's charging system by adding the additional battery, the result will be just the opposite. You'd be better off upgrading the truck's charging system wiring to handle the increased load of the audio system, and (if necessary) purchasing an alternator with more current capacity. It sounds like you're not planning on a very high-powered subwoofer system this time around, though; so it's quite likely that your stock electrical system can handle it without any need for an alternator upgrade.
Hope this helps!
Brian
