LED running off LiPo battery - full brightness for only 2 seconds

Hello,

First off, let me say that I'm very new to circuits and how all of it works.. This is probably something really easy, but I just can't think of why this is happening.. I just got a new Cree XPL LED in and soldered it onto my LiPo battery + charger that I have. I have it all soldered to the charging board via the through-holes on the side and I have a small switch between the LED and the charging board.. It was working fine last night, and today I decided to charge the battery. I unplugged it from my computer and turned the light on, and for 2 seconds it lit up the whole freakin' room.. Then the brightness drops drastically (down to probably 1/10 of what it was before)..

It's been charging for a couple hours and still the "Charging" light is lit on the board.. Either way though the battery should have more juice in it that when I plugged it in, so I can't imagine it's an issue with the battery.. Could it just be pulling to much amperage through the charger and is just being regulated down to something manageable? I can't imagine that's the case since it was working fine last night..

HELP!!!

Hi, One would indeed expect a little more juice from a 4400mAh battery.

It's hard to say what's happening, but I can think of a few things.

If the charger is USB-powered, you'll get 500mA max on a USB-bus and it may have to share that with other devices, which can result in a much... longer charging time. If it only gets 100mA, it will take at least a couple of days to charge from empty to full.

If, on the other hand, the battery is... fully charged, voltage will be quite high. Leds are quite picky, if you connect the led directly, without regulating current in some way, it can... easily ruin your led.

I unplugged it from my computer and turned the light on, and for 2 seconds it lit up the whole freakin’ room… Then the brightness drops drastically (down to probably 1/10 of what it was before).

Yes looks like you have fried your LED.
That is what happens when you let too much current go down it.

can’t imagine that’s the case since it was working fine last night…

Last night was the fluke, today is the reality. Something else was limiting the current last night maybe it was a poorly charged battery.

Ok, so after letting it charge fully last night, it was running fine this morning at full brightness. I plugged it in again this morning and when I got back from work I tried again. This time I unplugged it completely from the computer so the LED was running solely on the battery. Again with the 2 seconds full blast - then back to being dim. Plugged it into the computer and then it stayed bright for like 6 seconds.. Now the charger shows the battery is fully charged and it's running full brightness for as long as I keep the switch on.

Sounds go me like it's not a fried LED because it would just stay dim or not turn on at all... From what I can tell on the datasheet for the LED, and I'm pretty sure 3.7V is within it's acceptable variation..

You need something to limit the current to your LED, you have not got anything. You have a power supply impedance “problem” that is protecting your LED. We need a compleat schematic with part numbers and power arrangements in order to offer anything useful.

Hi, forward voltage of that LED is 2.95V, you are lucky that the internal resistance of the battery is sufficient to current limit and not overload your LED, but I don't know what its doing to your battery.

Have you a DMM to measure the battery voltage before and during the LED being connected.

Unless your DMM can measure over a couple of amps I would not ask you to measure the current when the LED is on.

Read the spec on the page to linked us to. (scroll down)

Tom... :)

I'd definitely create a schematic, but I literally just have the battery wired to the charger I have linked in my first post and then the LED going off of that.. What can I do to limit the current? I'll do some research myself, but if you could throw me a few links or can tell me what I need to put before the LED, that would be great!

Thanks!

You need a constant current LED driver of 3A or less between your supply and the LED.

guitarmaniak8: Ok, so after letting it charge fully last night, it was running fine this morning at full brightness. I plugged it in again this morning and when I got back from work I tried again.

Wow! Are you ever insistent on causing damage!

guitarmaniak8: Sounds go me like it's not a fried LED because it would just stay dim or not turn on at all... From what I can tell on the datasheet for the LED, and I'm pretty sure 3.7V is within it's acceptable variation..

And the rest of us are quite sure it is not.

TomGeorge: Hi, forward voltage of that LED is 2.95V, you are lucky that the internal resistance of the battery is sufficient to current limit and not overload your LED, but I don't know what its doing to your battery.

It's not the internal resistance. Adafruit make it - it is actually idiot-proofed! {See the description.} It is sensing a ridiculous load on the LED and shutting down. Remarkably, because it is in fact a rather heavy-duty LED, it has - so far - survived the abuse. How long it will survive - well, that will be interesting!