LED_ASAP
Enlightened
A fellow CPFer sent me two Li-Ion AAA cells and a Mag Solitaire. "Do whatever you can" to make it a Luxeon light /ubbthreads/images/graemlins/smile.gif
A Li-Ion cell and a Luxeon can easily team up to make a DD light; add an aluminum slug, drill out the reflector, a little filing of the battery tube... it shouldn't be a difficult mod /ubbthreads/images/graemlins/thinking.gif
Sure enough, after I have done these, a powerful light was born.
<font color="red">However---</font>
A Li-Ion has a voltage range of 3.0-4.2V during regular use, and a TWOJ has an average Vf of ~3.4V (3.27-3.61), with a pretty low dynamic resistance. In a DD light, when the cell is hot-off-the-charger, the battery draw can be well over 1A; as the cell is discharged, the battery draw (i.e., the brightness) drops progressively and pretty rapidly.
In my prototype testing, the battery draw started at 1.3A and dropped to 400mA in just 15-20min (I didn't note down exactly how long, anyway it wasn't very long). The light was really an egg cooker at the initial 1.3A /ubbthreads/images/graemlins/crazy.gif
<font color="blue">I got to put a regulator in---</font>
The MrAl's LDO driver is a good low part count CC regulator---But where to put it?
If I want to preserve the look and feel of a Solitaire, the functionality of its reflector, and the aluminum slug heat-sink underneath the Luxeon, the only space available for the regulator is maybe 1-2mm at the bottom of the heat-sink slug.
In other words, I need to squeeze the regulator into a ~6mm circle (including a rim of at least 0.5mm) and no more than 1mm high.
To make things more complicated, I have already epoxied the LS to the aluminum heat-sink slug when I did the DD prototype, and the (-) lead is permanantly connected to the slug by compression and epoxy /ubbthreads/images/graemlins/sick.gif I didn't want to risk ruining the emitter and try prying it off the slug in order to make the (-) lead insulated (which is required in MrAl's design). After some head-scratching /ubbthreads/images/graemlins/thinking.gif I figured I could get around by using P-MOS FET and PNP transistors to have a common negative instead of common positive in MrAl's original design.
The board was hand-drawn and manually itched. It just wasn't economical to make a single custom mod through a commercial board house or use a PCB designing software.
Now comes the fun of soldering some insanely small parts---SOT-23 sized MOSFET is the only "large" component, and sizes go all the way down to 0402-sized resistors. Here is the result: A Luxeon emitter, a 5mm Nichia LED, and a penny were included for size reference.
The wires were connected and the board was epoxied to the bottom of the slug:
As usual, the opening of the Solitaire battery tube was enlarged to accomodate this plug, and the reflector was drilled for the LS.
In this particular mod, battery draw is ~450mA. It starts at 480mA with a freshly charged Li-Ion and goes down to about 400mA just before dropping out of regulation. Here is a runtime plot:
The little light is really powerful for its size. It will easily outperform a typical 2xAA MiniMag with BB400 convertion:
And those "similarly sized" 5mm LED light, such as an Arc AAA, has no place to fight /ubbthreads/images/graemlins/tongue.gif
The point when you see a significant drop in brightness is around 3.1V. In regular use, this is when you should recharge the cell. The last-trace-of-light comes around 2.6V. This is considered as the critically low point, but it is still above the damaging voltage of ~2.5V. This light design should be very safe for unprotected Li-Ion cells.
Overall I am very happy with the result. It would be nice if I can find a way to put in a switching buck converter to improve the efficiency. However, due to the extremely limited space, a linear CC regulator may be the only practical solution for a Solitaire mod.
A Li-Ion cell and a Luxeon can easily team up to make a DD light; add an aluminum slug, drill out the reflector, a little filing of the battery tube... it shouldn't be a difficult mod /ubbthreads/images/graemlins/thinking.gif
Sure enough, after I have done these, a powerful light was born.
<font color="red">However---</font>
A Li-Ion has a voltage range of 3.0-4.2V during regular use, and a TWOJ has an average Vf of ~3.4V (3.27-3.61), with a pretty low dynamic resistance. In a DD light, when the cell is hot-off-the-charger, the battery draw can be well over 1A; as the cell is discharged, the battery draw (i.e., the brightness) drops progressively and pretty rapidly.
In my prototype testing, the battery draw started at 1.3A and dropped to 400mA in just 15-20min (I didn't note down exactly how long, anyway it wasn't very long). The light was really an egg cooker at the initial 1.3A /ubbthreads/images/graemlins/crazy.gif
<font color="blue">I got to put a regulator in---</font>
The MrAl's LDO driver is a good low part count CC regulator---But where to put it?
If I want to preserve the look and feel of a Solitaire, the functionality of its reflector, and the aluminum slug heat-sink underneath the Luxeon, the only space available for the regulator is maybe 1-2mm at the bottom of the heat-sink slug.
In other words, I need to squeeze the regulator into a ~6mm circle (including a rim of at least 0.5mm) and no more than 1mm high.
To make things more complicated, I have already epoxied the LS to the aluminum heat-sink slug when I did the DD prototype, and the (-) lead is permanantly connected to the slug by compression and epoxy /ubbthreads/images/graemlins/sick.gif I didn't want to risk ruining the emitter and try prying it off the slug in order to make the (-) lead insulated (which is required in MrAl's design). After some head-scratching /ubbthreads/images/graemlins/thinking.gif I figured I could get around by using P-MOS FET and PNP transistors to have a common negative instead of common positive in MrAl's original design.
The board was hand-drawn and manually itched. It just wasn't economical to make a single custom mod through a commercial board house or use a PCB designing software.
Now comes the fun of soldering some insanely small parts---SOT-23 sized MOSFET is the only "large" component, and sizes go all the way down to 0402-sized resistors. Here is the result: A Luxeon emitter, a 5mm Nichia LED, and a penny were included for size reference.
The wires were connected and the board was epoxied to the bottom of the slug:
As usual, the opening of the Solitaire battery tube was enlarged to accomodate this plug, and the reflector was drilled for the LS.
In this particular mod, battery draw is ~450mA. It starts at 480mA with a freshly charged Li-Ion and goes down to about 400mA just before dropping out of regulation. Here is a runtime plot:
The little light is really powerful for its size. It will easily outperform a typical 2xAA MiniMag with BB400 convertion:
And those "similarly sized" 5mm LED light, such as an Arc AAA, has no place to fight /ubbthreads/images/graemlins/tongue.gif
The point when you see a significant drop in brightness is around 3.1V. In regular use, this is when you should recharge the cell. The last-trace-of-light comes around 2.6V. This is considered as the critically low point, but it is still above the damaging voltage of ~2.5V. This light design should be very safe for unprotected Li-Ion cells.
Overall I am very happy with the result. It would be nice if I can find a way to put in a switching buck converter to improve the efficiency. However, due to the extremely limited space, a linear CC regulator may be the only practical solution for a Solitaire mod.
