I wanted a pair of LED-in-hilt sabers to be used for cons, sparring demos and costuming. Like most people on the forum it seems, I wanted the sabers to be as bright as possible so that they can look good in brightly lit environments. After spending months reading through all of the archived technical posts it became apparent that if I wanted a pair of super bright sabers that I would have to build my own.
Inspired by Sunrider's work with high power LEDs I did a search for the highest luminosity LEDs that were commercially available for sale to experimenters. The highest power single emitter LEDs that I found for sale were the Luminous Devices CBT-120 and CBT-140. I purchased one each of the 30 amp rated red and blue CBT-120s from DigiKey and one of the 5,000 lumen 28 amp rated CBT-140s from Mouser. CBT-120-B-C11-KM301 Luminus Devices Inc | 1214-1101-ND | DigiKeyCBT-120-R-C11-HK101 Luminus Devices Inc | CBT-120-R-C11-HK101-ND | DigiKeyCBT-140-WCS-L16-UA123 Luminus Devices | Mouser
When searching to see if there were any batteries able to power these LEDs that can fit in a saber hilt, I was surprised to find that Sony, Samsung and LG had a new line of high constant output current 18650 rechargeable Lithium batteries. The 2,500 maH, 35 amp rated continuous output LG 18650 batteries were available for immediate shipment at a reasonable price. A dozen of these LG 18650 batteries were ordered for this project. In Stock genuine high discharge rate rechargeable cylindrical 18650 Li-Ion
The XTAR WP2 II intelligent charger that I used for conventional lithium 18650s worked perfectly to charge these high current output batteries.
After some preliminary experiments operating high powered LEDs at reduced current drive using translucent polycarbonate blade with improvised collimators and a series of hacked together current regulators, I decided that the way I wanted to drive the blades was at their maximum rated current of 30 amps at a duty cycle of 50%, at a frequency of between 20 and 30 Hz, where the blade would have a live shimmer that would break up the static plastic glow tube appearance of the blade at constant level lighting.
I couldn't find any low dropout voltage, externally modulatable, variable current output, 30 amp current regulators that would fit in a saber hilt and be powered by a pair of 18650 batteries so I had to design and build my own.
The LED drive electronics is configured as three independently activatable, paralleled, 10 amp linear fold back current regulators. Activated simultaneously they provided a measured 30 amps to the LED. The linear current regulators are designed to have zero current draw when not activated and be rapidly switched on and off by low current level control inputs. A dimmer switch disengages activation of two of the three parallel regulators when reduced light output or longer run time is desired. Dropout voltage before loss of current regulation is about one volt. A 555 timer is used to generate a variable frequency square wave to modulate the regulators. The 555 timer is switched on by the LED output of the Nano Biscotte Sound Module V2 going active low.
A separate power supply consisting of four Eneloop rechargeable AAA batteries had to be used to independently power the Nano Biscotte sound card. The output from the lithium 18650 batteries being operated at 30 amps with constant square wave modulation turned out to be so electrically noisy that even with a regulator and filtering, the Nano Biscotte was constantly having randomly triggered sound and on/off events.
This saber project was very much a learning experience experiment in operating and powering very high current LEDs. The mechanical design of the saber was dominated by: heat management for the LED and current regulator, fast tool-free battery changing (10 minute operating time per charge at peak power), ease of disassembly and reassembly to replace burned out parts during circuit debugging, and ease of machining and re-machining the various mechanical parts. As such, this is a zero Greeblie saber with esthetics being totally ignored in favor of engineering function. The 4" diameter aluminum heat sink for the LED at the front of the saber though does double duty as an interesting looking and functional hand guard.
The electronics were mounted on a sled that was constructed from a section of 1/8" wall aluminum tubing with a 1 - 1/4" OD that matched the 1 - 1/4" ID of the hilt tubing. Areas of the inner surface of the sled were milled flat or inset to facilitate good thermal contact with the high current transistors and resistors. Arctic Silver thermal conductive epoxy was used to bond the heat generating components to the aluminum sled and LED heat sink. There is a threaded centrally located hole in the sled that the Covertec knob with an embedded 1/4-20 screw engages through a hole drilled in the side of the hilt to pull the sled into tight thermal contact with the inner surface of the hilt main tube.
The battery holder was designed to operate at high current and to allow rapid tool-free battery changes. Conventional conical steel spring battery contacts have too high a resistance (10 - 20 milliohms) to operate at 30 amps without overheating and collapsing the steel springs. The battery contacts are 3/8" diameter solid copper rod, directly soldered to the 14 gauge regulator and LED power wires. The front copper contact is set up to slide linearly and is spring loaded to tension the battery stack. The rear contact has a retention screw that rotates into a detent in the Kevlar-epoxy composite battery tube.
The rear cap containing the speaker and the AAA batteries is slid onto the rear of the hilt tube and is held in place by a knurl headed 1/4-20 threaded thumb screw. Loosening the knurl headed retention screw and removing the rear cap allows tool-free access to the 18650 battery tube, the Nano Biscotte microSD card slot, the mute switch and the modulation rate setting potentiometer. Battery swap time is about 20 seconds. Since operating time at full brightness is about 10 minutes, the ability to rapidly swap batteries without tools was an important part of the design.
The LED light output is collimated by solid aluminum reflectors pulled from Nitecore MT2A flashlights. As advised by Sunrider in his light focusing solutions thread, the rear surface of the reflector was cut back until the reflector, when placed in contact with the front window of the LED, showed an even reflection of the emitter of the LED over its entire area when viewed from the front.
How bright is the output of a 30 amp driven LED with a properly collimated reflector? LightSaber 30Amp BurningHoleTrashBag - YouTube
Here's a picture and a video of the blue LED saber illuminating a trash bag from the output of the blade holder and burning a blade diameter hole through the plastic. Definitely not something you want to stare into!
Indoor test - Brightly lit room.
All of the artificial room lighting is turned on. The front door and a 4 foot by 6 foot window to the left of the door are opened to let in the outside daylight. The room is brightly lit despite the appearance from the photo from having the camera f-stop and shutter set such that the saber blades did not over expose.
The sabers from right to left:
30 Amp CBT-120 Blue LED saber, Translucent polycarbonate blade
Master Replicas Anakin
30 Amp CBT-140 White LED saber, Translucent polycarbonate blade
White LED string driven at 6 amps mounted within a spinning light baffled blade. ( "Persistence of vision" TFU style Black Blade Saber)
The blue LED, despite having the highest radiometric (absolute optical power) output of the colored LEDs in the CBT-120 series appears relatively dim at 600 lumens compared with the 5,000 lumen CBT 140 white LED driven at the same current. There is a reason however, for selecting this Blue LED for construction into a high current saber despite its relatively low lumen output. The blue saber's high absolute radiometric power at short wavelengths is one of the key elements for an idea of how to build a daylight usable lightsaber blade.
[ Continued on - 30 Amp LED Sabers & Fluorescence Enhanced Saber Blades (Part 2 - Blade) ]