DriveEV Logo
JeepEV: Electric Vehicle Conversion Project
LED Lighting

     When it comes to lighting on cars, energy efficiency is typically not a concern, and as a result cheap, inefficient incandescent lamps are often used. However, lighting efficiency becomes much more of a concern for Electric Vehicles because reducing energy consumption even a little bit helps to fulfill the goal of achieving as long of a range as possible. This goal to reduce energy consumption as much as possible led me to convert the incandescent lighting on my Jeep to LED Lighting.

What? (Incandescent and LEDs):

If you're wondering what in the world Incandescent and LED refer to here's a fairly short explanation (okay, maybe it'll be a bit long):

     Incandescent lamps are the traditional type of lighting still used in many applications. Incandescent lamps contain a filament (like a thin wire) which is enclosed in a sealed glass lamp. When electricity passes through it, the filament begins to glow red hot (it produces light). However, Incandescent lamps aren't energy efficient; the majority of the power they consume is turned into waste heat rather than useable light. In general this means that incandescent lamps are grossly inefficient compared to other, more modern types of lighting (i.e. Fluorescent lamps, HID/Arc lamps, and LEDs). Although it is truly amazing that incandescent lamps are still being used 100+ years after their invention, I believe that they're "past their prime" and are no longer the best choice for many of the applications in which they're still used.

     LED (or L.E.D.) is short for Light Emitting Diode. LEDs are a relatively new form of lighting, and are popping up in more and more applications as the technology continues to mature. An LED emits light when electricity is passed from it's anode (positive leg), across a plate containing a colored dye, to its cathode (negative leg). A Single LED is typically only 5mm or less in diameter and encapsulated in epoxy. Their availability in extremely small sizes is a reason why LEDs have been and are used extensively for display/ indication purposes (such as in computers, VCRs, stereos, clocks, microwaves, etc..). However, LEDs also have many other benefits which make them desireable for use in a wide variety of applications. These benefits include:

     Traditionally the only downfall of LEDs is their relatively low light output. LEDs use to primarily be used only in indication applications where high light output is typically not required. However, as the technology has and is advancing, brighter and brighter LEDs are always being created. Some modern LEDs have achieved extremely high light outputs such as the Luxeon Star LEDs manufactured by the Lumileds company. Although, super bright 3mm and 5mm size LEDs are becoming very common as well.

How I used LEDs in/on my Jeep:

     Now (if you survived the technical section above), I'll talk specifically about how I've used LEDs in/on the Jeep. Before I forget, I'd like to mention that using LED lighting is in NO way a requirement for an Electric Vehicle conversion. However, it does provide many benefits (see the above list). The main reason I'm using LEDs on the Jeep is the power savings. What I've done (and will likely continue to do), is replace the wasteful incandescent lamps on the Jeep with custom-made modules of LEDs About this time you may be thinking "Modules? What...?" I use the word "module" to describe a group of LEDs assembled on a board with the necessary wiring to make them work and a way to connect them to the Jeep's electrical system. Almost every module I've made uses multiple 5mm LEDs. The reason for this is simple: 5mm LEDs are not yet bright enough to replace an incandescent lamp unless used in groups (the number varies with how much light is needed and what brand of LED is used). The reason why I've opted to use (at times large) groups of 5mm LEDs instead of a couple outrageously bright LEDs like the Luxeon Star is because 5mm LEDs are smaller, cheaper, and (in my opinion) easier to obtain. Below I've detailed the process I used to design, make, and install custom LED modules in various locations in my Jeep Cherokee.

Custom-made LED modules: Exterior: Rear Lighting:

     My first target for installing LEDs in the Jeep was the rear lighting, mainly the brake, tail, and parking lights. The existing lens assemblies in the Jeep hold a number of incandescent lamps: a 7 + 27-watt tail/brake dual-filament lamp, a 4-watt "small" tail lamp, a 4-watt side-marker lamp, a 27-watt turn signal lamp, and a 27-watt backup lamp per side. My first focus was to replace all the parking/tail/brake lights (both in front and back) because when you add up all the power they pull plus the headlamps, they put a big load on the 12-volt power system, which no doubt wastes a lot of power which would otherwise stay in the high-voltage system (since the DC/DC converter would not need to be dumping as much power into the 12-volt system to keep it charged.)

LED Lighting Page Photo LED Lighting Page Photo LED Lighting Page Photo LED Lighting Page Photo
The Jeep's rear lens/reflector assemblies (only driver's side assembly shown).

     Knowing that I'd be replacing a bunch of lights in the Red colored part of the assembly, I purchased super-bright 5mm red LEDs. The particular red LEDs I used were from and are rated at 20ma with a 2.2volt forward voltage. With that power they produce 8000 mcd at a 30 degree viewing angle (they are bright!). All of the rear red lighting was replaced with groups of these LEDs.

     I began by making modules to replace the two rear side-marker lamps. The incandescent lamps were 4-watt wedge based lamps. I decided that I could use the old wedge-style sockets, I just needed to use a piece of perf board of the correct size and I'd be able to plug it into them. Before beginning to make the modules, I first had to determine how many LEDs I'd need to use to produce the same amount or more light than the incandescent lamps did. To do this I hooked some LEDs to a solderless breadboard and inserted them into the rear lens/reflector assembly to see how bright they would be. using this method, I determined that 4 red LEDs put out plenty of light to replace the 4-watt incandescent lamps. Now that I knew how many LEDs I needed, I used a resistor calculator (since I'm lazy) to determine what size resistor I'd need to safely power the LEDs from the Jeep's 12 volt system. The resistor simply reduces the voltage and current to the LEDs to a safe level so the LEDs do not get over-powered which will ruin them. In this configuration I connected the four LEDs in series with each other and the resistor. I then cut out a piece of perf. board to the correct size (just slightly larger than the footprint of the 4-watt incandescent lamp), positioned the LEDs and resistor on it, and soldered them in place. I then plugged the newly made modules into wedge-style sockets and had energy efficient side-marker lamps!

LED Lighting Page Photo LED Lighting Page Photo LED Lighting Page Photo
The custom rear side-marker LED modules (Schematic drawing located here )

     The next LED modules I made replaced the small tail lamps in the rear lens assemblies (located below the main brake/tail lamps). The incandescent lamps which used to be there were about 4 watts each, just bright enough to make the reflective part of the lens assemblies glow at night. I determined that four of the 8000 mcd LEDs I had would produce enough light (actually more than the incandescents) for the location. I cut square pieces of perf. board to use as bases. On the perf. board squares I soldered the four LEDs and the correct size resistor (270 ohm). These new modules don't twist into the reflector/lens assemblies like the old sockets did. Instead, I glued the perf. board modules to the back of the reflector/lens assemblies. To connect them electrically, I cut-off and removed the old incandescent lamp sockets, and soldered the new modules' wires to the corresponding wiring on the Jeep.

LED Lighting Page Photo LED Lighting Page Photo LED Lighting Page Photo
The custom "small tail" lamp LED modules (Schematic drawing located here )

     After making the "small" tail lamp modules, I began making modules to replace the large brake/tail lamps. These modules were constructed like the "small" tail lamp modules, where the LEDs were soldered onto a flat piece of perf. board. What made these modules tricky is that they had to be made in a such a way that they could produce two levels of light (dim for tail lights, bright for brake lights). One method I considered involved using a set of diodes and two different valued resistors to adjust the amount of electrical current fed to the LEDs based on which circuit was active (tail or brake or both). This however seemed more complicated than it needed to be, so I came up with a similar (but simpler) method. I determined that I needed 20 red LEDs to produce the same light output as the incandescent brake lamp. So I figured to get dimmer light for a tail lamp, I'd just turn on a few of the 20 LEDs instead of attempting to light all of them at a dim level. After some playing around with the LEDs, I found that eight would produce sufficient light for the tail lights.

LED Lighting Page Photo LED Lighting Page Photo
Red LEDs, resistors, diodes, and perf. board will
become brake/tail lamp LED modules

     Like the "small" tail lamp modules, the brake/tail lamp modules' perf. board fits over the opening in the back of the lens assembly, while the LEDs stick into the lens assembly. It was a tight fit getting all 20 LEDs to fit in the existing hole in the lens assemblies, so I had to try out different configurations before I found out the best layout for the LEDs on the perf. board. Basically, I ended up with five rows of four LEDs each, with some LEDs skewed out of line where needed. Each series string of four LEDs is wired through a 270ohm, 1/4 watt resistor (on the ground side of the circuits). Then two standard 1N4001 diodes are used to control the brightness of the module. One diode's input is connected to the tail lamp circuit, while the other diode's input is connected to the brake lamp circuit. Both diodes' outputs are connected together and then to two (2) of the five strings of LEDs. The remaining three strings of LEDs are connected straight to the brake lamp circuit. Thus, when the tail lamps are on only 8 LEDs are lit, and when the brake lamps are on (regardless if the tail lamps are on/off), all 20 LEDs illuminate. Simple, right :-)

LED Lighting Page Photo LED Lighting Page Photo LED Lighting Page Photo
The components are soldered to the perf board and wired.
Schematic in drawing E7, located in photo gallery 20 (Click Here)

     After I assembled the modules, I tested them using my small AC to DC 12 volt transformer. I then wired and soldered them to the proper wires on the Jeep, and installed them in the lens/reflector assemblies. Luckily, the LEDs fit tightly into the holes in the lens assemblies, which keeps the modules in place. However, I also hot-glued the modules to the plastic backs of the lens/reflector assemblies to ensure they won't move around (though they have no room to move anyways).

LED Lighting Page Photo LED Lighting Page Photo
The LED modules are tested and installed in the Jeep

Custom-made LED modules: Interior: Instrument Panel Lighting:

     Many things in the Cherokee are illuminated by small incandescent lamps. Although incandescent lamps are very inefficient to start with, the small incandescent lamps used for indication purposes seem to be the least efficient. The Jeep had used these small lamps to illuminate the instrument cluster, climate controls, clock, 4x4 controls, etc. I decided to make good use of some super bright white LEDs to replace all the wasteful incandescent lamps that I could.

     The first modules I made consist of two white LEDs each. These are the 5mm size LEDs which have an intensity of around 10,000 mcd and a 10 degree viewing angle. I used these LEDs in conjunction with two 150 ohm resistors and a piece of perf. board. The result is a very low power replacement for the common "wedge" style incandescent lamps. Another plus (in my mind) is that these white LEDs produce a nice and crisp white light, which I favor over the yellowish glow of the incandescent lamps. No more dim, hard to read instrument panels!

LED Lighting Page Photo LED Lighting Page Photo LED Lighting Page Photo
This LED module is used to illuminate the transfer-case
gear label next to the transfer-case shift lever.

More Info To Come.... See Photo Gallery #19 for Pics
Remember, More photos are in the Photo Gallery!