This application is on an amusement park ride. I have 4 mr16 bulbs per car. There are 18 cars total. Our system uses a 32vac power supply and with voltage drop included our realistic power is 24vac.I am changing the voltage to 24vdc with a simple rectifier. We are replacing the 20watt halogen mr16 bulbs with Bulbrites part number LED/MR16DL. These leds use 12volts. What would you suggest for a reasonablly inexpessive restitor that I could use, and should I use some sort of current resistor? Thanks for your help.
You would not want to use a resistor to drop 24 volts DC to 12 volts DC. The resistor would become very hot, and would therefore need to be extremely large. I did not see the data sheets for this your MR16DL LED bulb, but lets just pretend it draws 250mA of current. The resistor with a 12 volt drop across it would dissipate 3 watts. You would require a large wire wound or ceramic resistor package. This defeaters the purpose of the LED light, as the system would become more efficient at generating heat than light. I am not familiar with the internal circuity of the LED bulb you have chosen. One suggestion would be to connect two bulbs in series, to the 24 volt DC source. If this configuration is not possible, your best solution is to incorporate a DC to DC converter at your 24 volt DC source, or an AC to DC converter from your 24 volt AC source. A single power supply to convert your AC to 12 volts DC would be most efficient, and would allow you to remove your existing rectifier circuitry. Finding a power supply with a 12 volt output should be easy, but finding one with a 24 volt AC input might be a little more challenging. If you have not purchased these LED bulbs, you may want to consider finding a substitute LED bulb designed for a 24 volt DC input. Some LED bulb that incorporate switching regulators even offer a wide operating voltage range. For example, 12 volts to 28 volts DC.