Converting 12v incadescent lighting to LEDs

Not counting the map lights up front, our campervan has three 12v lights in the cabin that run off the house battery. Each of these lights is an RV Luminaire Model CXL-12 from the Xantech Corporation. These lights have three 1A fuse style bulbs and a three way switch (off, 1 light, or all 3 lights). I especially like the ability to choose low, high, or off on the lights. However, I don’t like the 1A (per bulb) power draw, which is approx 12.5 watts (per bulb, thats 37.5 watts for a fully lit light fixture). True, a 70 Amp/Hour battery can power all 3 lights at full brightness for almost eight hours (if you fully discharged it, which you should never do), but LED lights are a lot more power efficient.

I thought about using a Luxeon Star I, III, or V Lumiled, but they would require separate driver electronics to be driven at 12V, and at $6 to $26 each they are not cheap. I’d have to wire three to four in series and/or be forced to use a very large resistor to manage the current (or, spend another 15-20$ for a good constant current driver circuit). To get LED lights that were already configured for 12v operation, I bought an auto work-light for $20 at Harbor Freight. It includes 30 5mm white LEDs in series, plus current regulating resistors. The worklight consumes 0.2A (20% of one incandescent bulb) at 12.5v and puts out about as much light as two of the bulbs (visual estimate). For your $20 you also receive some nice extras, like a cigarette adapter with long cord, battery to cigarette lighter adapter (with clamps), and a plastic tube.

Of course, the original circuit board has almost two inches of extra length that is not needed, so I cut it off with my wife’s hobby saw (don’t tell her). Based solely on the size of the remaining circuit board, I decided to replace two of the three incandescent bulbs with the LED’s. I had to drill out pop-rivets to remove the bulb holders from the fixture (using progressively larger drill bits in an underwhelming cordless drill made this take a while, but it was relatively straightforward).

Then, I removed the work-light switch (We’ll be using the original 3 way switch) and replaced it with a straight wire. Before mounting, I wrapped the back of the circuit board with black electrical tape to keep it from shorting out, and used carpet tape to mount it inside the light fixture. I soldered the LED circuit board power wires in place of one of the original lights such that the 3 way switch can select Off, LEDs only, and LEDs plus incandescent bulb. (If the LEDs were just a bit brighter I wouldn’t have left the incandescent bulb as an option.)

The result is a light that is twice as bright as the original at the 1 bulb setting (and takes 80% less power), and about the same brightness at the 3 bulb setting (taking 1.2A vs the original 3A). The LED’s consume 2.5W, and the remaining incandescent bulb consumes 12.5W for a total of 15W (vs. the original 37.5W).

Using a pre-built 12v circuit saved me a lot of time (soldering 30 leds in parallel and series can be a big pain) and gave me some useful leftovers (wire, cigarette power adapter, clamps). I could have really supercharged the lights by using three or four 1W or 3W Lumileds, but that would have been more expensive (especially if I did it right with a constant current driver), and quite frankly, it might have been too much light. I’m still considering trying out Lumileds, but with the varying voltages present (12v to 16v when charging) on the circuit, I’m afraid to do it without a constant current regulator that would add considerably to the cost.