The test done by djoss has me confused, to think that the led could handle more voltage as long as the amps didn’t reach the critical point, but that why i ask questions, thx
LumenDisaster you are right. LEDs can handle quite high voltages as long as the current is limited. That is an artificial setup so most people are correct that high voltage usually causes high current that kills the LED.
Two cells are used for 6 V LEDs that will not run on a single cell (without a boost driver). In your setup two cells do not make sense.
SST-40 has a quite low forward voltage (3.5 V @ 6.5 A) so it will run on a single 18650.
That’s not how it works.
V=IR
A driver that “limits current” will lower the voltage to reach that desired current based on the LED’s resistance.
The Vf and current of an LED are directly related by its resistance, just like a resistor.
You cannot magically feed it more voltage while forcing the current to be lower, because if you lower the current the voltage will need to lower with it.
If you feed 6V into any of these LEDs you can clearly see that the current will shoot to 20+ amps (off the right of the graph) and instantly kill the LED.
Well, I don’t know what kind of driver the M2 has. It would probably be the driver that would suffer from higher voltage first. If the driver can handle the higher voltage, and is a current regulated driver, then the LED would be buffered from any ill effects by the driver. V=IR only means that a current regulating driver has to burn off the excess some way in order to do its job of regulating current. As long as the driver successfully does that, the LED won’t know the difference. Technically, the LED will never care what voltage is in the system, as it will only take the voltage needed to light up at a certain current. If the current isn’t regulated properly, THEN your LED would have a problem.
A fet driver will deliver the entire battery voltage to the LED, and as you can see from the graph even even below 4v the SST40 is starting to reach the peak of it’s curve.
At 5v it would be drawing 15-20 amps and the output would be severely reduced due to heat (like what’s happening to the green line)
At 6V it would instantly die because V=IR would cause the LED to draw 20+ amps and burn up.
Depends if it’s a Constant Current driver or a Direct Drive driver.
DD drivers aren’t really drivers, they just switch the full blast of the power supply (battery) on or off.
(Lower modes are accomplished by PWM = basically switching on and off repeatedly, very fast).
So it only works with either high Forward Voltage (Vf) LEDs (like XP-L (HI) and XM-L(2) and XP-G2) or enough voltage sag of the power supply (either by means of a non optimal electrical path, a not so high drain cell or more than 1 LED in parallel).
That’s what limits the current AND voltage reaching the LED.
Constant Current drivers, as the name implies, limit the current electronically by reducing the Voltage to the LED accordingly.
What you want is a Buck Driver, or Step Down Driver.
Then you can use a 6 Volts power supply (like 2 LiIon batteries in series) to drive an LED with 3 to 4 Volts, depending on the Vf and the desired current.
Sorry I don’t think you understood what I meant.
I’m talking V=IR for the LED only.
You feed 6V to the LED, it will draw X current based on its resistance.
If a driver needs to regulate the current to something below X, it needs to drop the voltage.
For example,
It is not possible for an LED that draws 10A at 4V to be driven at 5V and still be limited to 10A current, since the R in V=IR doesn’t change much (it does just a little, due to heat).
This is why LED drivers exist, so that they can take that 5V and step it down to 4V in order to keep 10A going to the LED.
I’m tired of waiting for a boost or customizable step down driver to get back in stock,to run 2000lm on 3535 print, my lack of patience is going to kill my flashlights, but at least now i fully understand how the current works in these things
Okay. You were talking about the LED only. I was talking about the driver and the LED together. I wasn’t trying to take anything from what you said, but add some more information for someone who might not know.
