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So you want to add some electrical accessories to your new truck... |
First off, you need to identify what you've got to work with. The single most important thing to know is the output of your alternator. This is important because your alternator is your mobile generator - it actually creates ALL of the electricity that every electrical device in your vehicle uses (remember, the battery just stores it for future use).
According to Ford literature, the 1997 F-150 4x4's available in the United States all have 130-amp alternators. That's because all of these 4x4's came standard w/ V-8 engines, and the 130-amp alternator was standard with the V-8's. All other models probably have the 95-amp alternator, unless you opted for the Class III Trailer Towing Group (this option group includes the heavy duty electrical package which has the 130-amp alternator). Note that I said, "probably have"… If you have a 4x2 and got the optional V-8 engine, I'm not sure which alternator you might have. The '98 and '99 F-150's may or may not be the same as the '97's. It is my understanding that the '97 Canadian 4x4 F-150's models did not have the 130 amp alternator standard. It was only available with the Towing Package. Just goes to show you, When in doubt, check it out. Look at your "sticker" (if you've still got it) or ask the service manager to check for you the next time you're at the dealer. It is also important to note that the rated alternator output is a nominal value. If you've got a really good electrical multi-tester and know how to use it, you can hook it up to your alternator to determine the actual output. If you're unfamiliar with how to use the multi-tester or how to hook it up, I suggest that you leave this to someone else. You can fry it in a heartbeat (or at least nuke the fuse) and you will probably get a wicked shock. Unless you're doing something really exotic, and/or the amp draw of all of your devices is very close to the rating of the alternator, the nominal value is more than sufficient to design a system for most electrical add-on's.
If the demand of all of the electrical devices in your vehicle exceeds the output of your alternator, then two things can happen:
- If the draw exceeds the output for an extended period of time, eventually you will "suck your battery dry". If you were out in the boonies, then you'll really be S-O-L. Do this too many times and you shorten the life of your battery considerably.
- When the battery gives up everything that it has, then your alternator will still try to keep up with the demand. Eventually it'll "go south" too. Then you've got a Huge Problem!!!
Neither scenario is very appealing but luckily there are a couple of options. You can either increase the power generated (get an alternator with higher amp output) or increase the stored electrical supply by using a battery with increased storage capacity (aka "deep cell" batteries). You can even use a multiple battery setup (a battery for starting the vehicle and one or more batteries to power the other stuff). Even if you use this type of multi-battery setup, it is important to remember that there is still a limit to the stored power that is available. I'll cover batteries in a future article, but suffice it to say that the alternator is the only place where electrical power is generated in our vehicles, and therefore is the most critical element in the equation.
BUT WAIT!!! Before you rashly run out and buy a high output alternator and a couple of auxiliary batteries, let's figure out what you NEED, and then you can spend some time considering what you WANT. Simply put, your NEEDS are the electrical demands for all of those devices that your vehicle currently has. If you wanted to be really anal about it, you could pull out your multi-tester and determine exactly what the draw actually is for each electrical device. This would be very accurate, but it would also take a lot of work.
You can get a fairly close approximation by using the following chart (courtesy of 4-Wheel & Off-Road magazine, December 1997). This will give you a "ballpark" idea of the amp draw for various pieces of standard equipment.
| Electrical Circuit | Amperage |
| Air Conditioner | 12-20 |
| Backup lights (two) | 3-4 |
| Brake lights (two) | 3-4 |
| Cigarette lighter | 10-12 |
| Clock | 0.5 |
| Dome lamp | 1 |
| Headlamp dimmer | 2 |
| Headlights (two, low beam) | 8-9 |
| Headlights (two, high beam) | 13-15 |
| Heater/Defroster | 6-10 |
| Horns (two) | 20 |
| Ignition | 2-4 |
| Instrument panel and gauges | 4 |
| License plate light | 1 |
| Parking lights (two) | 2 |
| Power door locks | 5 |
| Power seat | 25-50 |
| Power windows | 25-50 |
| Side-marker lights | 2 |
| Starter solenoid* | 10-15 |
| Taillights | 5 |
* Although it's listed as starter solenoid, it's actually the starter motor that causes the big draw, not the solenoid (which is nothing more than a large relay).
You will note that some items are shown as a range of values. This is because different vehicles use different types and manufacturer's of equipment, and this equipment may have different demands. That equipment whose ranges vary 2-8 amps from high to low aren't as much a concern as the high draw devices like power windows and power seats. These have a fairly wide spread between their high and low values and can quickly eat up the available "juice".
You'll also notice that there are a couple of obvious items that are not included on this particular list. A radio is one. If you've got one of those "killer" sound systems and like to make the truck bounce while going deaf, then you'll want to plug in whatever ridiculous wattage output your system is run at. A "normal" listening level for a typical vehicle radio draws about 2 - 3 amps.
Another thing that's not listed is windshield wipers. These will draw anywhere from 3 amps at low speed to 6 amps for full speed swipe in monsoon mode.
You could play it safe and take the worst case (highest draw) for each item but that's probably being overly conservative. You need to realistically consider how and when each item is used. For example, it's a pretty safe bet that your low beams and high beams won't be on at the same time. You also probably won't be trying to adjust your seat while you're putting your window down.
A pretty straight forward way to analyze your current demands is to identify the greatest number of devices that would be on all at once, and use the highest value for their respective amp draw. This will determine the high end of your demand range.
Then, minimize the number of devices that will be on at any given time and use the lowest value for their respective amp draws.
This will determine the low end of your demand range.
Add the high end value to the low end value, divide by 2, and then multiply by 1.05 (this adds a 5% "cushion" just in case you underestimated some of the demands). This should give you a fairly "safe" average working demand value that is specific to your circumstances.
Let's use my truck as an example. I have the XL model with optional A/C, so…
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* On the 1997+ Ford's, the A/C compressor is on w/ the heater/defrost setting. I'm assuming that the draw of the A/C system is at the low end of the range (12 amps) and therefore add to it the high end draw of the heater/defrost (10 amps) for a max. climate control value. I'll use the min. A/C draw for the min. climate control value.
72.5 max. amps + 49.5 min. amps = 122 amps.
Divide 122 by 2 (to get an average) = 61 amps.
Multiply by 1.05 (a 5% safety factor) = +/- 64 amp average working demand.
Note that I'm not including the starter solenoid (motor) draw since I usually don't try and start my truck with everything already turned on (that's just me). I also don't smoke, so the only time I'll use the cigarette lighter is with my portable compressor or radar detector, and radar detectors are usually a tad unnecessary for off-road jaunts (I'll talk about adding off-road lights in a minute).
Now that I know what I NEED (64 amps +/-), I should look at what I WANT.
We'll again take my truck as an example. I wanted to add lights. Just a "a few" though. Up front I want a couple of wide angle driving lights (55 watts each) along with a couple of amber fog lights (also 55 watts each). I also want to add some more light while I'm backing up, so I mounted a couple of 55w lights on either side of the hitch. I also want some powerful off-road/long-range/pencil-beam lights (100 watts each). For now I'll mount a couple of these to my grille/brush guard and but anticipate on adding 2 or 3 more on a rooftop lightbar in the future, along with a couple of flood lights (100 watts each).
Wow, that's a whole bunch of lights!
Time for a reality check. First, let's break it down to see what each light draws. Remember, watts divided by voltage = amps. 100 watts/12 volts = 8.33 amps for each LR and floodlight. 55 watts/12 volts = 4.6 amps for each driving, fog, and aux. backup lite.
Add it all up and I WANT to add 1030 watts or about 86 amps worth of illumination!
Let's get real for a second and discount the future lights (the ones on the lightbar), and consider the draw for just the lights that I want to install now. This would equal (100*2)+(55*6) = 530 watts or 44.2 amps!
Knowing that I won't have the fog lights on with all the other lights, I'll back out another 110 watts (9.2 amps) from my total. This means that if I had the driving lights, LR's and B/U's all on at once, they would draw 420 watts (about 35 amps).
Let's see. I've got the 130-amp alternator, and my existing equipment draws about 64 amps. That leaves me with about 66 amps to "play with". Subtract 35 amps for the max. load of my new lights and that still leaves another 31 amps or so for future "stuff".
Even if I use the max. draw value for my existing equipment (72.5 amps), the 35 amps of proposed auxiliary lighting still leaves me with another 22 amps or so for future "stuff".
I'm in pretty good shape for now...but, I'll have to reconsider adding those (3) 100w LR's and (2) 100w floods!!! (That's almost 42 amps!!!)
OK. Let's say that instead of a 4x4, I had a 4x2 XL w/ the 95-amp alternator. My 35 amps of new lighting would be really close to maxing out the capacity of my alternator. I'd probably want to cut back somewhere.
It's also interesting to note that a 4x2 XLT or Lariat with power seats/windows/locks would pretty much be maxing out a 95-amp alternator - AS IS! You would need to be very careful about adding a bunch of other electrical stuff.
Having the optional Ford 130-amp alternator, allows you so much more flexibility for add-ons. If you're still shopping for a new F-150 and are considering auxiliary lights, a winch or an ear shattering sound system as possible add-ons, then I would highly recommend opting for the Towing Package or forking out for the higher output Ford alternator. Otherwise, an aftermarket high output alternator may be one of your first add-ons.
In the next article we'll take a look at how to wire up your add-ons to keep them from doing "bad things" to your truck.