a small quest for perpetual light

copyleft 2007 by Ralph Klimek .
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My quest for light began in 1965. It was Christmas Eve, Good Saint Nicholas had dropped by. He left behind a little science kit for this 6 year old wannabe  physicist.  It contained some batteries, a functional and annoyingly loud electric bell, some switches, miscellaneous hardware and a handfull of small edison screw light bulbs.  I was about midnight, my parents and  guests has adjourned to another room leaving me alone with my batteries and light bulbs and the dark. The light had been extinguished to encourage me to leave and join the others for an evening Christmas Eve supper but I didnt care. Not only had Saint Nicholas visited that evening but the God Prometheus, the ancient giver of light, had also visited. In the dark I admired the small light from my battery and light bulb. It was was the most compelling and beautiful thing that I had then seen. I think I know how the amazing Edison must have felt some eighty years earlier. An ancient tyranny, the monster from realm of darkness had been temporarily conquered.

A perpetual light it wasnt, and by the next day the glorious little light was extinguished. The battery drain from even this little light killed it in only one night. The Lord of Darkness had returned, beaten but not vanquished.

But all that was allmost fifty years ago. Saint Nicholas returned only once more and Gods only visit you once. The incandescent light has served us well, it is extremely simple in principal and practice. Its ability to convert electrical energy to light was only bettered 70 years after its invention by the flourescent mecury arc lamp and finally in the seventies Monsanto released to the public the very first red light emitting diodes. I saved up my pocket money and ventured into town to the electronic parts place and purchased one red light emitting diode. Wow, only took 20 milliamps and put out this feeble deep red glow, just barely visible in daylight.   Thirty years later again I go to town to buy one of these new fangled white LEDS. White indeed! What a load of cobblers! And EFFICIENT too! This I had to see to believe. Prometheus has been back. The result was the small hand held LED torch in this image. There are three nickle hydride batteries recovered from some long forgotten mobile phone, a switch and ballast resitors. It was an very serviceable torch. Then one day, the inevitable occured. I needed it, and in my dark toolkit was the drained LED torch.  Emitting the obligatory expletive I managed without it. A little later I paused to observe that allthough the batteries were well and  trully drained the marvelleous little LED was still producing light. I had not attended my toolkit for about 7 days and it had been left on that long. How much light was it producing?  With dark adapted eyes in a dark room enough to read by.  Then the God spoke. (Just a metaphor mind you!) Measure the current, it said, so measure the current I did. About 50 microamps. Hmmmm.

Think about that ! I added a shunt resistor to the power switch on my torch to let it have a steady drain of 100 microamps to produce a light source that cannot be put out. Its cheerfull little beacon allways beckons in the dark and produces enough light to read by. A fresh charge in the batteries gives it a full on time of over 7 days. The image here just shows the glow of the pilot in broad daylight.

Another LED torch I  made to amuse the children and to show them that white light can be synthesized from red green and blue light. Try this at home. It never ceases to amaze me that the reflected light from this torch appears to contain all colors in the correct hues. Once again the power switches are shunted with 100Kohm resistors. This produces a very serviceable night light for children as well as a usefull source of light.

RGB 3 color recombination demonstration with 100Kohm switch shunts the light is still clearly visible in daylight at night
one charge lasts over 12 months at this level allways welcome in a dark room

After a power blackout, my elderly mother tripped and breaks her hip. Just a few years ago this would have been considered the end of ones life. She recovered thanks to private health cover and a metal prosthesis. I made my parents a gift of light that they had made to me all those many Christmases ago. It is allways on, they now never fumble for a candle and matches when the power chooses to depart. It is so bright that they cannot abide it in their bedroom at night but its perpetual beacon lights the corridor nearby. A set of cheap AA batteries lasts about one year in this class of service.

This torchs now reflects my growing ambition and lust for power .  Only a couple of years ago a company called Luxeon releases LEDS of assorted colors with input power ratings of up to 3 watts. This torch is based on a one watt white LED and some old laptop nickel cadmium batteries. I produces a dazzling output with only 100 milliamps and a fully charged battery gives a usefull burn time over 8 hours. Naturally the power switch is shunted with a large value resistor so that I can find it in the dark. Next to do a switch mode current regulator. The 5.6ohm resistor that acts as a current ballast gets quite warm in normal operation. A significant gain in battery life could be achieved by improving this with a switchmode regulator. The next version of this power torch will have a lithium ion cell and switcher. The goal is to produce a lantern that can burn at full intensity for over a day on one charge. A solar cell on the back to keep the battery topped up would add a nice touch.  This lantern has been extensively used for general purpose portable lighting and after maybe 300 hours on time the led luminous output has dropped noticeably.  The blue white conversion phosphors are meant to do this over time but I was not expecting the degradation so quickly. The lamp was not being overdriven, allthough being a clone led, and just following the specification for it, still resulted in it being actually overdriven. The lesson here is, as usual, except no  imitations.

Luxeon clone 1 watt white LED these old cells give about 8 hours burn time
the clone 1W luxeon a high gain yellow LED provides an allways on pilot light

Using a genuine Luxeon 3W white led and hight capacity LION cells, for the second last word in portable lighting!

the led requires a generous heatsink3Watt Luxeon ledblue led is allways on
red led shows charging voltage ready

This lantern, so bright that I will not call it a mere torch, uses a 3Watt genuine Luxeon led.  The energy source is a pair of large format Sony lithium ion batteries.    The 5 terminal regulator is provided to perform charge management of the Lion  cells.  LED current management is provided, somewhat wastefully, with the 10W ballast resistor. It gets very hot in operation. The Mark 2 version  will have a switchmode constant current regulator.  With a full charge on the cells, there is about 8 hours worth of useable light, which with a switchmode regulator should improve to about 18 hours continuous operation on one charge.

The 3W LED is a miracle, at least by my estimation.  There are better leds available now, made by Cree  , however I cannot source these in retail quantities in Australia yet.  The big Luxeon led cost me all of AU$6  , manufacturers' seconds stock, normally retail for about AU$30 each.

Lion cells are dangerous beasties, they must be handled with care and respect. Short circuits will result in fires, poor handling will result in degradation of the cell capacity.  The Lion cell is a remarkable and new technology using unconventional electrochemistry. These cells were recovered from a discarded notebook computer nearly ten years ago.  They have either been in storage or active use in that time and they still retain at least 70%  of their factory  amp-hour capacity.

My electrical safety features a resetable solid state fuse, ballast resistor  and simple charge manager.  The charging regime for Lion cells of the LiCo04  type  (cobalt oxide)   is constant current charging at 1Amp for a couple of hours or untill the cell open circuit emf reaches 4.2V whereupon charging MUST cease.  A Lion cell MUST NEVER be float charged, a Lithium fire will result if you persist in this folly. I never leave mine charging unsupervised, even though the 5 terminal regulator will cease charging at the specified voltage I still charge under the controll of a timer.  The charge managers inside the battery module of modern notebook computer cell modules contain a small microprocessor and analog electrics that monitor , measure and record the ingoing charge and outgoing charge and begin and terminate the charge cycle based on this measurement.  As the cells mature, their actual and published performance charge and voltage specification diverges.  The cell module controller's view of the internal state of charge no longer reflects reality and it will declare the cell to be defective.  This is why new battery modules only seem to last about 1 year.  There is generally speaking, nothing wrong with the cells, it is the module manufacturers erring on the the side of caution in a litigious society. I have opened many discarded Lion cell packs are only once found some genuinely defective Lion cells.

I have elected to use a pair of Lion cells in series, this gives me up to 9 volts at open circuit after a recharge. Two cells in series still affords some measure of cell charging safety, dont put more than two in series. There is a risk that one or more cells in a series string could become fully charged whilst others are still accepting charge. You MUST NOT attempt to charge to a fully charge LION cell. It will result in the formation of internal Lithium metal dendrites that will short circuit the cell internally.

I allways monitor the cells condition with a voltmeter to ensure that they both have a similar open circuit voltage before commencing a charge.  These Lions are considered fully charged when their  open circuit emf is 4.2Volts and completely discharged at 2.5Volts. Never discharge a Lion cell below this or irreversible internal structural damage will occur. The constant current source emf during the constant current mode charge should be limited to 4.5Volts per cell and the knee point set to about 4.1Volts.

My advice to the curious is do not futz around with Lion cells unless you accept and mitigate the risks.  Do , however, play with 3Watt leds; they are dazzling  ....amazing in fact.   If you are just playing around use NiMH cells, they have high capacity and pose no safety issues.  

The Next Step in perpetual lighting.

The next led torch of mine will be closer to the ideal of the perpetual light. Consider the series resistor in line with the led, the resistor only lets through the required 10 to 100 microamps required for a pilot light, nightlight.  Given that from real world AA batteries we may drain nearly 100 microamps and get allmost the the shelf life of the battery anyway .What if the LED was pulse modulated to 30mA peak but 100 microamp average current. The apparent light output would provide a very usefull lantern that gives nearly the shelf life of a standard battery. Tests of mine support this theory. What I havent solved yet is a suitable pulse driver that in itself does not consume more than 50 microamps. My current circuit using a 74HC14 cmos hex trigger/inverter comes close. I used a cmos hex schmitt trigger basically to make the oscillator simple allthough this stage draws the most current because the first gate is self biased into a linear mode because of negative feedback. The other stages operating as saturated cmos switches draw essentially no static current. It produces a very acceptable flashlight beam and draws about 1mA .  (Do not try this with a 74HCT14 they draw nearly a milliamp just sitting there) Next to try CD4093.

gate 12 is a simple schmitt trigger oscillator, buffered by gate 34. the high value resistor and low value capacitor provide a slight pulse delay. The 2 diodes form an equivalent OR gate resulting in a narrow pulse thats buffered by gate 98. This gate can directly drive the LED but for max optical output it drives any small power mosfet directly. The led series resister can be dispensed with after testing and design is comleted. Unused gates must be held low else the total chip quiescent current drain is higher than it might otherwise be.  With these component values I measure a total average current drain of about 1mA and this results in a very bright light source.  My target is to obtain a "useable" source of light that draws an average of 100 microamps which would give essentially the shelf life of a commercial disposable dry cell. The output transistor must be a mosfet, zero gate drive current and essentially zero drain source offset voltage.

And on a completely differant tangent, I do well remember the long Saturday afternoons in the sixties watching "Epic Theatre" , the old "sweat and sandles" epics. It would allways amuse me to see the heroes venturing into forgotten ancient and abondoned catacombs and sewers.  How did they see ? There were allways flaming torches on the walls!  I think in the the "mummy" series of B grade horror flicks, the about to be cursed archaeologist ventures into the ancient tomb. There are  flaming torches lining the ancient unused corridors.  What a marvellous ancient technology! A flaming torch that burns without attendance for 3000 years and completely fails to fill the ancient tomb with soot and carbon monoxide! Maybe the "curse of the mummy" was actually cabon monoxide poisoning from all those ancient flaming torches!


added lion cell lantern notes and images   Wed Feb 17 18:46:41 EST 2010