Now that you know the basic theory behind automotive electrical systems, it's time to put it into practice in building your overland vehicle.  You will see the mantra "No modification happens in a vacuum" often here on Flatwater Overland.  That's because many people who modify their vehicles fail to take into account the second and third order effects of the modifications.  It is rare that you can add or remove something from a modern automobile and not experience consequences of some kind.  Most vehicles today spend thousands of hours in the develop and engineering stage to create a mass reproducible product that will function properly for anyone in any market it is sold in.  Since overlanding can be considered "extreme" or at least "heavy duty" use in the minds of most automobile engineers, we must take extra care when modifying the original product- even if it is designed for off pavement use.

Prior to  installing all those cool lights and electrical accessories, an examination needs to be done to determine if your vehicle can handle the additions without some major electrical surgery. Chances are that a 21st century SUV will be able to, but a small 4x4 from the 1960s-2000 likely won't be able to.  How does one go about this kind of personal enlightenment?  The first thing to do is determine the level of charging and storage capacity your vehicle came from the factory with, or is presently saddled with.  As mentioned, if you have a true 4x4 mid to full sized SUV built since 2001, it is likely you can add the accessories you will need without serious additions to the charging and battery department.  If your truck has dual alternators or an alternator rated over 135 amps, you will likely be secure using the factory electrical system.  However, if you are driving an older 4x4 with minimal factory trim and an alternator at 100 amps and below, you should plan on spending some significant cash on upgrading your electrical system.

Before we get too far into buying custom alternators and dual battery systems, some homework needs to be done in regards to your current or planned electrical accessories.  Here is what Flatwater Overland suggests you do to get started on this trail.....

Determine the combined additional load.  What accessories are you going to add, and how much load do they add to the vehicle?  This can be very complicated to figure out, but let's simplify it some.  Let's discuss "constant load" versus "impulse load":  Constant Load items are electrical accessories that create a long-term or constant resistance when utilized.  These are items such as lights, radios, inverters, and fan motors.  Impulse Load items are only used occasionally and are not generally added into an overall electrical charging plan.  These are items like winches.  Going back to old man Ohm, we need to figure out the total additional constant load we will conceivably be adding to our overland vehicle.  We will begin by assuming that the manufacturer built the vehicle with the capacity to operate all factory installed components with the alternator and battery it was equipped with.  This, however, may be a bare minimum of accessories.     

  1. Determine the current load of each accessory you are adding.  You may need to use Ohm’s Law to figure this out, but we need to get the maximum operating amperage of each accessory.  For example:  You want to add a pair of off road halogen lights, an inverter to run a navigation computer, a 12 volt fridge, two-way radio, a winch, and maybe some “rock lights”…  Those lights are rated at 100 watts each; so I=R/V which is amps=watts/volts, this gives us 8.3 amps=100 watts/12 volts…times two since there are two lamps.  The inverter to run the navigation laptop is 200 watts (rule of thumb when calculating an inverter is 1 ampere per 10 watts of output), so 20 amps (the laptop won’t actually pull that much current, but you need to plan for it).  The 12 volt fridge pulls 1.3 amperes when running according to the manufacturer.  Planning on using two 35 watt lights for the rock lights, so that’s 6 amps total there.  The two-way radio uses between 1 and 5 amps when operating, so let’s just assume 2 amps average.
  2. Do I need more alternator?  Adding up all of these constant load items gives us a maximum of about 44 additional amps we will be needing to run everything when on the trail.  44 amperes!  That’s a lot, and this a fairly conservative list.  So, we would need an alternator that can put out at least 40 more amps in normal operation than the factory alternator just to keep up.  Have you ever thought of this when buying your gear?  How about an example-  Older Jeep Wrangler from the 90’s or 2000’s is usually fitted with a 60 or 90 amp alternator, this means you would need at least a 100-130 amp alternator to just run these items.  This upgrade can be accomplished not too difficultly.  If you consider putting all these things on a luxury SUV not meant to use them, finding that alternator just got more difficult and expensive.  The upside to this is that many modern SUVs have 130 amp alternators and better from the factory.  The better SUVs are equipped with power outlets and inverters already to handle the computer and fridge complete with 160-200 amp alternators.  But what about a winch, or other impulse items?
  3. What about the "extras"?  Impulse load items are not typically added into standard operating load calculations because they are not typically used frequently enough to demand special attention.  However, we should talk about winches and other high-load devices.  If you do not plan on installing any high-load devices, then you can skip forward.  But, just keep in mind that if you have a winch and end up needing to use it for more than a couple pulls, you are going to seriously tax your charging system and should consider a custom, high output alternator and dual batteries if technical trail driving is in your future.

Streamline your present and planned electrical system.  If you can afford to do so, it would be wise to streamline your electrical loads in order to minimize overall current draw to a minimum level.  

  1. The easiest way to streamline is to convert all of your vehicle’s lighting to LEDs or HIDs.  Light Emitting Diodes and High Intensity Discharge lights have become more affordable and commonplace, but still carry a significant price premium over traditional halogen and incandescent lights.  These lights, LEDs in particular, have distinct advantage when it comes to minimal power draw and lamp life span. 
  2. Minimize and simplify electrical accessories.  Ask yourself if you REALLY need that accessory.  Remember how current adds up!  Only install it if you will actually use it.  Resist the temptation to have more than you will regularly use.
  3. If you have not yet purchased your desired overlanding vehicle, consider buying the model with the lowest trim package you are comfortable with.  This will not only reduce the overall complexity of the truck but also reduce parasitic voltage loss and give you greater leeway in adding electrical accessories.  Fewer factory accessories mean more of your accessories and still be able to use a factory installed alternator.