Quote:
Originally Posted by TheGerman
The super cheap LED lights consist of just LEDs and resistors. These have a narrow operating range and can start to flicker/turn off as battery voltage drops.They also only work when the polarity is correct (might need turned around to work). The polarity issue is an easy way to spot these.
|
While I agree with much of what you said, I think you have the resistor-circuit a little off. Typically in a resistor led drive circuit, for 12 volt operation, the LEDs are hooked in series (three? LEDs in series) and then a resistor is added, also in series. As the LEDs each drop about 3.3+/- volts, the resistor is dropping the remaining voltage to the supply - e.g., in the three in series example, at 12.5 volts battery, the LEDs drop about 10 volts and the resistor about 2.5 volts. The circuit is actually very well behaved with dropping or rising voltage - as the voltage increases, the voltage drop on the resistor increases, increasing the current though the LEDs, and increasing the light output. The LEDs will continue to light (but will get dimmer) as voltage decreases until the voltage drops below the "threshold " voltage for the LEDs (about 9 volts in the three LED in series example). No flickering on and off. The circuit is inherently polarity sensitive, as you state - but some resistor drive LEDs use a diode bridge to eliminate polarity sensitivity. Resistor LED drive circuits are RF noise free and are easy to dim, by adding an external resistor. Unfortunately, some low end resistor LEDs use underrated resistors, which fail prematurely (I find this more of an issue than the brightness variation with voltage).
An electronic drive circuit also may or may not be polarity sensitive, and is more likely to "flicker on and off" with low voltage. The electronic driver tries to maintain constant output current to the LEDs over a range of voltages, keeping light output constant when the input voltage changes - e.g., same brightness when boondocking on battery power at 12.3 volts as when plugged in or on generator with the converter charging the batteries at 13+ volts. As the electronic drive circuits often use high frequency oscillators to accomplish their task, they are the source of the RF interference issues some have reported (TV or radio noise or loss of signal when the LED lights are turned on, dimmed, etc.).
Personally, I have had excellent results with resistor style retrofit LEDs in our Solera. They are dimmer when we are on battery power, but are sufficiently bright that I have several on double throw switches with a dimming resistor in one position - can just throw the switch to the bright (no added resistor) position if more light is desired. I have encountered some issues with early failures - stopped using that brand. Other brands have been excellent- no failures in five years and over 300 nights camped. Zero RF interference.
FYI
Jim