"Are there LEDs made for such a high voltage?" Not 48 for $7 including shipping half way around the planet.
"Perhaps each LED is actually a pair in series?" Not by the looks of the guts.
Reducing the current will extend the life.
I would maybe rewire it for 12V by separating the 8 quarters. Series 2 quarters and give that section its own resistor. Repeat 3 times. Meaning 4 resistors. More reliable.
LEDs don't follow Ohm's Law. Best to measure the current (in all 4 sections individually) in the final layout before calling it done. Expect to need quite an assortment of resistors.
Another option for more efficient 12V is running 3 quarters in series, 3 more in series, then the last 2 in series. The 12V battery drain will be reduced by 25%. G-[ Parent ]
A no brainer for people like me is to just make a special 6 volt battery pac with a large enough capacity to last all night....
I give up on Leds for a really good light for now.
I rather like the 4 watt fluorescent lamps for $4.75 clearance sale at Walmarts for now.
Who knows....someday they may have A large surface area LED lamp??? ( :>) Norm[ Parent ]
That is, it didn't have a "resistor" inside, it had a constant-current source inside.
These LEDs would operate safely and indefinately (without a series resistor) on anything from 3V to about 14V if my memory serves correctly.
They were about twice the price of a standard LED (at the time), but the space saving and convenience in driving them was well worth the difference.
I've probably still got a few in my junkbox...
I just had a quick google for them but find no (modern) references for such a device, so perhaps the "here is a LED, here is a driver, you marry the two" design philosophy has taken over.[ Parent ]
http://josepino.com/circuits/?pwm
I had a few differences in mine, which was referenced from a different source and tweaked by experimentation, namely that I used a 500K pot (because they were available), and had resistance in series with one of its legs to reduce the duty cycle as I did not want the individual LED's to be of too high of intensity (as expected, the first thing they did was try to shine them in each others eyes). Also, I had a capacitor across the power input leads as the circuit developed a lower frequency flicker without it. I also had a third 4148 connected across the output in case of any minor inductance, as would typically be done with a motor controller.
This is a very blurry photo of the circuit. There are only a few components, and it is just on a proto-type board. One could likely make it much more neatly than I. There are six leads from the board, power+, power-, three leads for the pot, and the negative lead to the led's.
Happy Scouts with their lights. I did not measure its efficiency, but I expect it is fairly efficient with a low power 555, and relatively high resistances on the r/c portion of the circuit. Adusting the resistance to lower the duty cycle further would likely be needed but should be doable to run your LED's from a 12V source, as I did run one of these test circuits at 12V as is with it turned down, but had I have turned up the pot I am pretty sure I would have blown the LED's. I also have three led's hooked in series to a slightly different 555 pwm circuit running at 12V now, which I used for plant starting in the spring.
A slightly more complicated version had another capacitor so that the operating frequency and the duty cycle could both be fine tuned, but that was getting a bit complex for 10 year olds (and me as well), although it did operate better. Anyhow, I was just thinking that something like this might work well, and efficiently for your lights, although based upon what you appear to have paid, it would be a significant portion of the cost. Rich 'A Joule saved is a Joule made'[ Parent ]
Thanks for the other comments too. Yes a PWM circuit would be nifty, but seems like way too much work and expense relative to this $7 lamp.[ Parent ]
If you can do it with a switch (no time lag between the comparison)... may want to check "how bright" they are to human eyes in the dark with higher value resistors. May find there is almost 0 difference between the 33 and 51, but the current goes down (better LED and battery life).
Could be impressive for a night light with a total of maybe 5~10ma to the entire light. The ones that light will be very efficient. They won't all light with cheap LEDs (or even good LEDs). Hi-Lo switch can be SPST, with a ~1K resistor jumping the terminals.
I agree about the PWM in a $7 light. But I have used the cheap housing and changed the LEDs to better LEDs. Not sure it made sense either. :)
Be nice to see 5mm white LEDs with built in current regulators. That would be handy. G-[ Parent ]
Efficiency is nice, but I'm also trying to set up a lamp that is fairly bright, not a night light. With both parts at 52 mA, the total would be 104 mA or 1.29 W supplied, of which 1.01 W reaches the LEDs, spread over 36 LEDs, or 28 mW each. (1.5W total reaching LEDs if using 33 ohms.) [ Parent ]
