I soldered 36 red SuperFlux LEDs on stripboard with 9 current-limiting resistors. The LEDs used 53mA each. I mounted them in the plastic case of a compact cassette tape (remember them?).
It was a night-light that was way too bright. The heat from the LEDs crazed and yellowed the clear plastic of the case even though I had many cooling holes top and bottom and tall feet.
I bought some cheap Chinese flashlights as Christmas gifts. They have 24 white LEDs on one side and 3 white LEDs on one end. They came powered by 3 Super Heavy Duty AAA cells (they are not super and are not heavy duty). The flashlights cost 4 bucks so I paid for the batteries and got the flashlights for free. They are very bright and my flashlight has been used for many hours and is still bright.
I wonder if the LEDs will burn out soon if I use name-brand alkaline battery cells?
Hi audioguru,
Wow cassette tapes, i thought i was the only one left on the planet that still had some ha ha.
I had quite a few Chinese knock off flashlights go on me, the LED's would start to burn out one by one. Even worse, the LED's would first start to blink on an off and that would be very annoying when trying to see something important.
One was a name brand flashlight so i was surprised this would happen. It was the only one i cared enough to look into and i found that they were driving the LED's at 50ma. These were the small 20ma white LED's that we all know and love, and they were using 50ma through each LED so they could get the brightness. Of course that is way too much current for prolonged use, so it the light was left on for a while one LED would start to blink on and off and if left on longer more would follow. I ended up breaking the LED's off with a large pliers to leave only the good ones, but eventually they start to go too so i replaced the whole bunch of them with a Luxeon Star high power LED with appropriate limiting resistor. It's been working ever since of course, but what a pain.
So the moral of the story is if it looks cheap and it's bright, then check the current level. If it is more than 30ma expect problems (20ma LED that is). They can take abuse, but not 50ma of abuse for a 20ma LED.
They might be using those heavy duty batteries so that there is more voltage drop as you already thought of, so when going to alkalines there will be less voltage drop and thus more current. The difference can be quite a bit too, so what i would recommend is if you really like these lights then load in some alkies and then turn it on and check the current with a good low series ohm meter or shunt. If it is more than 30ma per LED then it could end up blowing the LED's over time. It may take a while of run time though, one of my lights did not blow right away it took a few uses of prolonged use to start seeing the blinking.
But all it takes is a little more resistance in series with the battery as im sure you already know, so the only challenge is to find a home for the new resistor and make sure it can stay cool enough to last a long time.
For my 'good' light, i mounted the new resistor in the head and left the clear bezel off so that it gets good cooling from air just outside of the head. Seems to work pretty well as it has been in use now for some two years or so without a problem. Dropping is another issue though, so the resistor has to be solidly mounted too.
Good luck with it.
I bought some cheap $1 lights a while back and they work great for a little while until the LED's start to blink, but i find that if i dont use them for prolonged periods (like only a few minutes at a time) the LED's stay working ok. It's only when they run for a longer time that the LED's heat up too much and start to burn out with the tell tale blinking...which is worse than if they just burnt out entirely with no light output at all.