kaz911
Active Member
Can you explain #3
Every LED light has a power supply/regulator - some don't and rely purely on resistors (don't even try those) - Power supplies spec'ed/designed by western companies - built in china are generally much better.
I'm not an EE but I understand OHM's law quite well and the constant voltage drop across a diode and in this case an LED. I would need something better than (don't even try these)
Thanks,
-Mike
Resistor based power dividers are fine for PRE regulated power where you know that you get 13.6 volt all the time. They are not very good for automotive where power fluctuates between 11.5 - > 14.5 volt - often with high spikes from engine turn on/turn off.
Just do the calculation with ohms law... First do it 11.5v 20ma - then on 14.5v 20ma... So pure resistive drive of LEDs are not the smartest for automotive. You would need (homebrew) somewhere from 500 - 750 ohm to drive a single LED plus you need 0.5 watt resistors (you design with 40% safety margin) - Even in SMD 0.5 watt is a relatively large sized resistor (In SMD they are usually around 2010 size)
But then there is little or no protection. My figures above are far below what you will really see in Automotive electrics. Normally we calculate with power surges from around 6 volt to spikes of 36-80 volt or more when I design for automotive use. The moment your alternator stops pumping power (when you switch the engine off) - you might see spikes of close to 90 volt on the supply line. That is deadly for only resistor based circuits.
For Automotive use (alternator connected) the only right way to power high brightness LED's is with a constant current source power supply. Nothing else is safe. Alternative is to put a 13.6 volt regulated power supply on your cabin lights switch/breaker. Many companies do them for marine use - like Mastervolt for example.
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