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Discussion Starter #1 (Edited)
The Electrical System ExplainedBy Gil "usmcdoc14"
Fortin
[ PART 1 ] [ PART 2 ] [ PART 3 ]
From A to B
So now you know how to choose your wire, your fuse, the switch and how to connect it all up. But in order to put it all together we have to start back at the beginning: How is this all powered?
A: The alternator
Now with a "normal" jeep you have many options to upgrade your alternator, but you own a JK. The JK alternator is controlled by the wonderful management system in your vehicle so just "slapping on a 200a alternator and hit the trails" is not going to work. When the aftermarket gets on the ball to allow a safe bolt on upgrades then I will update this section. But luckily the 2007 came with a 160a alternator and then they down graded it to a 140a one. This is still a LOT of amps for what came factory! Remember, you have to have more amp draw than what your alternator can handle before it dips into your battery reserve. Another option is use a diesel JK alternator or another Daimler Chrysler alternator of the same design that is higher amp. The main thing here is add up your amps and see if you are cutting it close.
B: The Battery
The battery is the soul of your electrical system. It is what starts your jeep and runs everything when the engine is off or the amp draw is above the alternators output. You can drive home without an alternator till the battery goes dead but you can not start an automatic transmission JK without a battery.
The battery is the most important part of your electrical system and if you are going to upgrade anything you should start there.
A 12v automotive battery typically consists of layers of positively and negatively charged lead plates with insulated separators between each plate in a cell. The cells are filled with an electricity-conducting liquid (electrolyte) that is usually distilled water and sulfuric acid. This causes a chemical reaction that releases electrons, allowing them to flow through the conductors to produce direct current electricity. Each cell produces a set voltage of DC current and when ran in series equals the total voltage of the battery. As the battery discharges, the acid of the electrolyte reacts with the materials of the plates, changing their surface to lead sulfate. When the battery is recharged the chemical reaction is reversed. Repeat as needed.
Basically there are two types of lead acid batteries and they are starting and deep cycle. The starting battery is designed to deliver a high amp output quickly (cranking amps) The deep cycle battery has lower cranking amps usually but a greater ability to discharge for a longer time (reserve capacity). Internally they are designed differently as they serve 2 very different jobs and it mainly has to do with the thickness of the lead plates. Now keep in mind that a deep cycle battery does not always mean it should be used for something that requires a high amp output like winching, they are usually designed for a lower amp draw over a long period of time like with lights. You can use them if the cranking amps are high enough to start your jeep but for the same size a regular starting battery will have higher cranking amps.. They you will have a few "dual-purpose" batteries out there that are a combination of the 2. Your best bet is to read the specifications on that battery and see if you are getting short changed on cranking amps or reserve capacity.
Now these two types are broken into 3 sub-categories of how the electrolyte is stored inside: Wet cell (flooded), gel cell, and Absorbed Glass Mat (AGM) Wet Cell
The wet cell is the "basic" automotive battery and is hundreds of years old. Its simple technology that works. By wet cell they mean the electrolyte is in a fluid just sloshing around in the battery. They comes in two styles; Serviceable and Maintenance Free. Both are pretty much the same except you can open the caps on the serviceable and check/adjust the electrolyte solution. Like I said, the electrolyte is a liquid in there, crack the case or open the caps and it will drain/spill out all over the place.
Gel Cell
The electrolyte in a Gel has an additive that causes it to be jellified or semi-solid. They work great in very deep cycle discharge but can be picky. The recharge voltage on this type of cell is lower than any other styles of lead acid battery. If they are rapidly recharged the gel will separate and create a void and can permanently damage the battery. Hydrogen gas is a by-product when rapidly charging a battery, so think of it like blowing bubbles in a milkshake. They are "sorta" spill resistant, because after recharge they can still be liquid for some time till the electrolyte re-gels. Gel batteries are not as common as people think, most because they are confused with the next kind.
AGM
Absorbed Glass Mat. Inside AGM batteries the acid is absorbed into a very fine glass mat. Unlike a gel or wet cell there is no free moving electrolyte at any time, so they can be mounted in any direction because they can not spill, even when punctured they will not leak since all the electrolyte is contained in the glass mats. Those glass mats also allow a higher purity in the lead plates because they do not have to support their own weight and can be thinner as they are trapped in the sandwich of mats supporting them. This makes them very durable in a high vibration environment that would kill most others. The thinner plates also allow more of them to be in the same size case increasing its reserve capacity. The purity of the plates also allow a higher amp current. The lack of water inside them makes them freeze proof. They fully rock, they will do your taxes, they will scratch your back and make you waffles with bacon.
You are seeing a lot of win for the AGM battery in an off-road vehicle, so you are wondering what the down side is.
Price.
You will pay more for a quality AGM battery, but in that same money you will get a battery that will outlast anything else. Also 2-3 times longer life in normal use and immeasurable increase in survivability in a Jeep.
I bet on survival and I installed AGMs in all of my vehicles, specifically Odyssey batteries. ODYSSEY Battery - Official Manufacturer's Site
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I used to run another brand but after killing a couple hundred dollars worth of "off-road" rated batteries I changed my loyalties. "Bad batch", "abuse" or whatever killed them is moot, they died and never at a good time or location. I have been running Odysseys for a while on and off-road, I even had an electrical problem during a deployment that drained them to near nothing before anyone noticed.
I have not killed one yet.
You can even get them with a metal case should you want the outer case un-killable as well.
No matter what battery you choose, use a real battery holder. Batteries are heavy and the last thing you want is a lead filled box that can easily cause a fire bouncing around. There are many companies that offer great mounting options that are inexpensive. Don't be hack and use bungie cords or ratchet straps, this is not safe no matter what your buddies think.
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I am running a dual setup with an isolator/combiner. I like this setup as it allows me to remote switch to combine both batteries as one.
You have a lot of options here as vendors sell everything from a big switch to a mechanical remote setup or a full electronically controlled system. When batteries are ran in series (positive to negative) you double the voltage, as you can guess 24v is NOT good for a 12v system. But when ran in parallel (positive to positive, negative to negative) it combines the cranking amperage and the capacity.
But no matter how you run your setup, single or dual battery, do not skimp on the wiring. Do not go to your local big thumpin' stereo place to get wire. Usually they have a thick useless insulation and VERY small and sometimes undersized gauge wire inside despite the markings. Get actual automotive wire or wire that is rated for the power that your battery will be stressed with. I recommend going to a local welding shop and buying "welding lead", it is much less expensive but much higher quality than anything that you can get at the auto parts store. It has a very durable and oil rated insulation layer with a fine strand core that makes it flexible to route easily. I recommend nothing smaller than 2ga. Use the charting above to give you an idea of what you will need and remember that if you move the battery you will need larger gauge wire the further away you re-locate it from the original location.
Use quality battery terminals for your connections. Some people like to get the blingy gold plated ones from that thumping stereo place that you should watch what kind of wiring you get. To be honest, they usually have a very good selection of them and they work. I like military or marine grade terminals so I get these as they are simple and work.
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It's a keep things simple terminal with no little allen screws to corrode or get stripped out.
Everything gets a properly installed connection or lug. The welding shop can swedge the lugs on for you or you can do as I do an solder them. Then adhesive lined shrink tube and lastly a label.
Label EVERYTHING, as you get older, you forget stuff, label it!
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A label maker is your best friend when doing wiring, buy one. I buy my wire in bulk so I may have 5 "blue wires" and 4 "red wires" so I trust nothing unless its properly labeled. A black wire does not always mean ground and a red one does not always mean positive. Label every wire and do it well, not only for yourself but for anyone else who may have to work on your vehicle.
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Next we will cover a bunch of the stuff we bolt on, wire up, clamp to or other wise tax our electrical systems. Pimpin' aint easy.
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* CLICK HERE FOR PART 3 *

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