So I have 3 of these leds in the picture hooked up in series with a high power driver but the driver needs 10- 20volts to operate (I bought them connected like that).
What I would like to do is just use one of them with a 3.7 lipo, will this work?
I know that the forward voltage is 1.4v so that leaves 2.3v left for a resistor to cover or something like that, dont understand that part yet.
So what im asking is what resister would I need with my lipo and I need to push that led to its limits so its very bright.
You could use a string of 2 of them too - leaving 0.9V for the resistor or so (but allow
for 4.2V fully charged voltage, that's 1.4V for the resistor so 1.8 ohm 2W or so would
work (it will dissipate 1W, but you don't want it screamingly hot).
For a single LED you'd need 3.6 ohm 3W.
Whatever the case you'll need to heatsink those LEDs if operating at a high duty cycle.
There are also constant current drivers which have the advatage of being in a TO220-like
package that can be bolted to a heatsink. I forget the part number(s), something like 4101
As mark said above - I was going to say that, but he covered it. Use a 3W resistor.
I'd recommend using a constant current supply. You can get cheap DC-DC converters with current limiting on ebay.
A less efficient way that's more precise than a resistor would be a linear constant current driver like the AMC7140, but I don't think that part will run off 3.7v. (there may be similar parts that will). 2 AMC7135's in parallel would do it (and IIRC they work well on low voltages), I think...
If you're really dirty, you can use a constant voltage DC-DC converter, and adjust it through a current meter to get just the right voltage to get the desired current, and leave it at that. This doesn't provide particularly good voltage control, but you can get away with it on high power LEDs - they have significantly higher dynamic resistance than indicator LEDs (as in 0.x ohms, give or take an ohm - we've measured it). IIRC the IR ones are kinda pricey - so maybe you'd better not do this to them.
Be careful with those things - you need heatsinks, and you should take care to not hurt your eyes with them. They're extremely bright, but they don't look bright, and don't trigger your reflex to close or avert your eyes.
Be careful with those things - you need heatsinks, and you should take care to not hurt your eyes with them. They're extremely bright, but they don't look bright, and don't trigger your reflex to close or avert your eyes.
Thats probably why ive got a headache haha because ive got 3 of them powered up and me looking at them.
I think they have a constant current driver but it needs a minimum of 10v to work and those small lipos are damn expensive, Im going to use a resistor for now just to test my stuff and will check on ebay for a better driver.
