I bought LED H4 headlights a long time ago and tried them until I was told they are illegal so I'm going to use them in an old broken house lamp but I'm having a little trouble understanding the "draw" side to the specifications of the LED's, below is the ones I have and I've tried using just 12 volts @ 4 amps and its works fine but if the input is 9 to 32 volts does it always just use up to 13.8 volts because it has a voltage regulator? I haven't tried using a multimeter on an empty headlight socket yet to see what voltages are being used in the car but is 12 volts safe to use because of the draw? I understand the amps side where if a device needs 1 amp is ok to use a 2 amp power supply
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It’s a little complicated to provide a full explanation, but for a simple explanation it is helpful to understand the difference between an electronically controlled LED and the (uncontrolled) incandescent bulb.
A traditional incandescent bulb can be thought of as a resistor, and using ohm’s law, the current will increase with the voltage. So, the bulb will draw more current (and be brighter) at 14.4V than at 12V. This is why you can often see yellow-light headlights on old cars with faulty alternators at night.
LEDs have a different voltage-current characteristic. They are almost ‘constant voltage‘ devices when they are on, and increasing the voltage slightly can result on a large current increase. So, instead, LEDs are driven by a ‘constant current’ source. This is what the ‘driver’ in an LED does - it provides a constant current to the actual LED elements in the light.
But there is more! There are a couple of ways of providing a ‘constant current’. The old fashioned way was using a ‘linear regulator’ which is effectively an electronically controlled resistance in series with the LED to keep the current at a steady/constant level. This varying ’resistor’ arrangement means that system will draw a constant current no matter what the voltage is, and the difference (in energy) is dissipated as heat. This is (probably) not what you have.
The more modern way is to actually electronically ‘transform’ the current using a ‘switching regulator’. It’s moderately complicated, but for the purposes of the explanation, it can be considered as an essentially loss-less process - power-in equals power-out, so the current drawn from the power supply will actually decrease as the voltage rises (to keep the power V x I constant). So if it draws 1.6 A at 13.8V (V x I = 22W) it’ll probably draw 0.8A at 27.6V (V x I = 22 W). This is probably what you have.
