When we first purchased the 340, one of the things I noticed was that many of the switches on the dashboard didn't "indicate" properly. To clarify - many of the rocker switches on the dash have small, built in incandescent indicator lamps. When the switch is turned "on", these lights illuminate, so the operator knows that circuit has been activated. But, over time, a couple problems inevitably manifest:
1 - Since the lights are incandescent, the do eventually burn out, leaving that circuit without a status indication.
2 - Incandescent bulbs generate a substantial amount of heat, and, over time, that heat degrades the plastic of the switch body. Eventually, the switch body may start to crack around the bulb, and the little bulb starts flopping around inside the switch.
So, what to do? My answer is to replace the bulbs with LEDs. Light Emitting Diodes solve both problems, since they have a life that is vastly longer than incandescent bulbs, and they generate far less heat. A couple suitable LEDs are here:
The royal blue one (1000 mcd) isn't as bright as the deep blue (2000 mcd), but either one will work quite well. They have basically the same dimensions as the incandescent bulb being replaced, so they snap right into place, and the O-ring seal around the bulb is still effective.
Now, if you look at the specifications for these LEDs, you'll note that the forward voltage is specified as between 3.0 and 3.6 volts (we'll use 3.3 for calculations). As such, a resistor is required in the bulb circuit, to drop the voltage into this range. Assuming worst case for a boat operating at roughly 14.4 volts, we see we have to knock (14.4 volts - 3.3 volts) 11.1 volts out of the bulb circuit for proper operation. Using Ohm's law, and the example of the Royal Blue LED (30 mA forward current), we have 11.1v / 30 mA (1000mA / 1 A) = 370 ohms. So, a roughly 370 ohm resistor needs to be in the circuit with the LED. At this current level, a 1/4 or 1/2 watt resistor is sufficient, and fits in the switch case with ease. These work fine:
In the next post, I'll show an actual switch conversion - stay tuned!