Where to get LEDs rated for 1 to 1.5v

Joel,

There are not many (if any) visible spectrum LEDs that will run directly from a single AA battery.  But, most of the inexpensive solar/LED devices, using a single AA battery use a device (like cx2601) that has a voltage boost inside.  I suspect that the 'green' component, with multiple stripes is an inductor (part of the boost circuit).  I believe that if everything is working correctly, a normal LED should work fine.  There are a lot of articles on the web concerning solar/LED lamps, that could help you identify the components on your LED driver board (and battery charger).  Search on cx2601 or 'Solar LED hacks' for some interesting read (and potentially some help).

Good luck!

Gene

Stanley makes red LEDs that work at 1.5 V.

Maybe the circuit is boosting the voltage as it flickers.

Try it with your 2V LEDs to see...

For some reason that shade of green ("vintage kitchen green" is a popular color with inductors. Don't know why : )

Hi Joel,

For the reasons Gene mentions, it is not possible to test the LED with the battery alone, i.e. it will only work when connected in the circuit.

As mentioned earlier, this circuit from a solar light is a fairly common one and uses an inductor to boost the voltage to run standard white LEDs of about 3V forward voltage drop.

Unfortunately, due to the nature of physics, to get LEDs for 1V to 1.5V would mean they would emit mostly in the infrared region, as the forward voltage drop is related to the P-N junction band gap and hence the energy of the photons emitted. For example, Deep UV LEDs often require 5.5-6.5V to run, whereas IR remote control LEDs can run at about 1.5V. For more information, you can see Wikipedia under Light-Emitting diode - Colours and Materials.

- Gough

Forgot to mention -

LEDs are polarised components. The amber colour requires less voltage than the white that you are replacing and should work. There's a good chance you may have hooked it up backwards, your solder joints aren't good, there's a broken wire somewhere or the battery contact is a bit duff. But replacing white LEDs in solar lamps with coloured LEDs generally works fine.

On an LED, the flat side of the unit leads to the negative side, and the long leg is the positive side. You can try checking with a multimeter to ensure your polarity is correct as getting it wrong will mean no light, even if the voltage/current is sufficient.

- Gough

Hi Joel,

I was set up to do some experiments this evening and so I decided to take apart a cheap dollar store outside LED light and check the voltages. I knew that they operate on one 1.25 volt NiMH battery so these LEDs have to be similar to what you are looking for. Because of how cheap they are I expected to find an LED that was running on 1.25 volts. This was not the case however. The unit contained a special 4 leaded IC YX8018 which in conjunction with the rest of the sparce components (1 inductor)  produced square wave output to the LED of 3.72 volts.

Here is a picture of the output as read across the LED. This is more than enough voltage to light a standard LED. The pulsing also serves a secondary purpose by extending the life of the battery since power is only applied to the LED for a percentage of the time. Incidentally the image on the scope is inverted as I have the leads of the scope reverse polarity on the board due to the difficulty in getting the large ground clip into place on the negative terminal. If your LED isn't lighting there is a pretty good chance that there is a problem in the circuit.

John

Thanks to all who’ve responded.  The idea of an inductor that boosts voltage makes a great deal of sense.  I can see where the AA battery would not work directly, and my suspicions that the 2v rating for the LED means just that and is not a “max” is confirmed.  In my relatively simple mind I envision the inductor building voltage through resistance in a nanosecond, releasing it at 2 volts that activates the LED emission, and repeating the cycle producing the effect of the candle flicker.  The self-flickering LEDs I “just-in-case” bought shouldn’t be necessary.

I am aware of the polarity for the LED wires and was careful to correctly solder the black and white leads to them.  My biggest inhibitor is my essential tremor.  If you don’t have that malady yet, pray that you never do.  It makes it exceedingly difficult to hold a soldering iron, solder, and wires steady enough to get a clean result anymore.  I try using normally spring-closed tweezers and other heat sink devices to hold parts together, and brace my hands on things, and when workable an alligator clip/magnifier/wand holder stand, but it’s still a frustrating challenge.  So forgive any sloppy-appearing workmanship in the pix.

It would appear that the green device I thought was just a plain but large resistor is more so the inductor “coil”.  Although it does have continuity across it, perhaps it’s not working to boost the voltage as intended.  Or as you’ve suggested, one of the other components is faulty.  There’s only 2 diodes, a 4-pronged transistor (I think), and whatever the flat round brown component is.  The diodes have continuity in one direction okay, so I reckon it could be the transistor, which if what I’ve read is correct may be involved in the boost function?  I’ll also use my Optivisor headband magnifier to more closely examine the board for a micro-cracked or slopped solder point.

As per Gene’s idea and cx2601 reference, I checked this article:  1.5 VOLT WHITE AND UV LED DRIVE CIRCUIT   .

Its over my head in a lot of ways, but does offer insight that I can appreciate.  Shabaz, Douglas, and Gough... all your input has also been enlightening, so I now understand a lot more than I did.  It may come in handy in dealing with the other solar garden lanterns of various kinds in the future... a year doesn’t go by without at least one of them going belly up for some reason like corrosion, old batteries, spiders, or needing a new solar panel.  Some flicker (the best ones) and some don’t.  And to John, who helped this past week on another frustrating electrical repair project, another big thank you for the time and expertise you’ve contributed.

I can take a couple more closeup pix of the cboard if anyone would like, appreciating any more analysis.  They are the simplest and most inexpensive lanterns we have and I’ve been tempted to just chuck them, but their effect at night is the most realistic of all.  It’s just that they have a history of not coming on in the evening after a day or two, which was frustrating, and why I tried disassembling one last year.  I suspect the panel in full sun all day isn’t enough, despite needing to charge only one battery (all our others use two).  Cheap lanterns or not, my curiosity and determination to learn and repair stuff perhaps has the better of me.

Joel

addendum:

Okay, I always thought a capacitor was barrel shaped.  Apparently the brown disk shaped component I referred to in a paragraph above is known as a disc capacitor.  I see them in most circuit boards, but didn’t know what they were.  I’ve known “barrel” capacitors to fail, so why not this disk version, esp. if it’s supposed to store the built up voltage, and isn’t.

Disk capacitors are generally ceramic type, owing to its material nature, it's almost like a solid layer of ceramic with conductive metal layer deposited on the ceramic dielectric to form the capacitor. The assembly is then dipped in some protective paint/coating. It's a simple construction that lends itself to fairly reliable low-capacitance value capacitors, although if moisture gets in, the conductive metal layers could (in theory) oxidise and stop acting properly as an electrode, with consequent reduction in capacitance value.

The round "barrel" type is likely to be an aluminium electrolytic capacitor. These are generally much larger value capacitors formed by "rolling up" electrodes soaked in electrolyte, insulated with plastic film. This assembly has much larger area resulting in higher capacitance, which is then shoved into a metal can with a sealing rubber bung from which your two terminals protrude (for the radial type, anyhow). These capacitors typically get used in power supplies and often fail because of a number of reasons - namely that they deal with high amounts of ripple in power supplies (a stressful application), that they (like every non-ideal capacitor) have an equivalent series resistance (ESR), that the ripple current through the ESR causes the capacitor to heat up, and that the electrolytic capacitors are sensitive to heat as this causes the rate of evaporation of the electrolyte to increase which also increases the ESR (which forms a runaway feedback loop) to my knowledge. As a result, these capacitors often "cook" and blow their vents (low-quality electrolyte formulation doesn't help) or they end up drying out (sometimes due to poor seals around the rubber bung) which reduces their capacitance to non-useful levels.

- Gough

Hi Joel,

An interesting post - I'm sure countless numbers of these, often cheap, solar lights end up in landfill/incineration but luckily not yours...so well done trying to repair them.

Lots of good comments already re: the voltage boosting. A non-technical term for this type of setup is sometimes known as a Joule Thief . The phrase was coined to detail a circuit that extracts all the energy from a single cell battery...and the standard designs work well.

Rod

Except for my sloppy soldering where the black wires attach to the board, I can’t see where anything grounds across, nor do I note a microcrack at a connection, an issue I’ve found on a Microwave oven board and a TV converter box.  I may try to redo that power point solder job on a day my tremor is diminished.

By the way, I did a little looking and verified the device I thought was a resistor is indeed an inductor as you fellows said.  Hidden under it on the board is the wave symbol for inductors... it includes an “L”, but my electronics books don’t indicate what that means.  There’s many forms of it, but I’m guessing it’s maybe a ferrite coated radial choke inductor.  It’s bands are perhaps not red-green-red-silver, but rather brown-green-brown-silver, which I take to be 10% tolerance 150 uH, although the sites selling them didn’t say what uH stood for.

One questionable status is the transistor... on close examination there’s rust on its pins.  Could this be indicative that it’s the culprit rather than the inductor?