Quote:
Originally Posted by fit7ad
High school physics teaches us that P = V * I. This is true even if you drop the voltage across a diode instead of a resistor. You will need huge heat sinks to dissipate that kind of power.
A better way is to use a PWM circuit with a power MOSFET. You can look for DIY kits/circuits or DC motor speed controllers. You might still want a bypass switch for 100% brightness since the controller is not 100% efficient and it probably won't give you 100% duty.
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I just knew I shoulda went to high school!
I've used small diodes for years to drop voltages, but never really ran any at high currents. Down at a few MA, they down seem to make much heat at all.
Anyways, it's not that much per diode. 5A x 0.7V = 3.5 Watts each.
Depending on the size of the diode, you might not even need a heat sink..
I remember about 35 years ago making a 12V 30A supply for a ham radio project. I mounted the 4 diodes on a big heat sink that was bolted to the chassis. So, I never noticed it getting hot. But, one cold winters day,
I was out in a cold radio hut and noticed how warm it was by my old 12V PS.
Running about 20A, it must have been putting out a lot of heat from the whole chassis..
Anyways, I was wrong about the lamp current too.
Since adding the diode drops in series with the lamps will increase the overall circuit resistance and therefore drop the current (saving some battery/Alt power)..
At the cost of less candle power..