I tried to post this over at BatterySpace (in their contest area) hoping to win a GC from them, but it has disappeared since this morning with no explanation. I hope the same does not happen here :-D
I know this has been done before, but I had to try and I think it turned out well. For the price of this light (see below) I could have bought a decent bike light, but this is more fun (not really). Thanks to the people here, MTB forums and slkelectronics.com for the ideas and for posting them.
Below is a step by step of what I did to build this light and the parts and tools it took. I am sure I will do it differently on my next one and there are going to be some changes to the parts to I think. The parts were sourced from various places such as Mouser, BatterySpace, Ebay, LedSupply, RCaccesssory, Sandwich Shoppe and DealExtreme (for the optic and Q5 LEDs).
This was my first battery pack with an A123 cells, which have a lot of promise (hopefully they will ramp up their production and we can get them in cars one day).
Part Qty Price
Wired Buckpuck 3023-D-E-1000 DC Powered 1 $18
2 C-Cell MagLite Flashlight 1 $16
Perfect XR19 Cree Heatsink - C (PXR19-Ce) 1 $16 (many other options)
Arctic Alumina 1.75g 1 $3
PolySwitch 730 --- 7 Amp limit 1 $1
Thermostat --- 70 Deg C limit 1 $3
PVC (160mm) Heavy-Duty Thermal Shrink Tube 1 $4
12 AWG Silicone Wire Red/Black 1 $5
RIS Rail (Ebay) 1 $5
Cantilever 30mm mount for Aimpoint (Ebay) 1 $5
PL1040B Pelican 1040 Watertight Hard Case 1 $14 (not yet here)
Ultra Plug Set 2 $3
Cree XR-E Q5 Emitter on Star 4 $8
Computer Power Cable 1 $0
Waterproof Connectors 4 $20
Total $148 (approx)
Soldering Iron and solder, solder wick if you need it
Voltmeter (helps to have one with continuity tone function)
Butane jet lighter (to remove stars from the emitters if necessary)
Hacksaw and vice
sealant glue (or whatever glue you want to use to hold the tailcap on)
Straight and round files (these should be a good size, not the small ones)
Hex wrench set
Pliers and screwdrivers
Probably some other stuff like sandpaper and the wirestrippers, etc.
Step 1: Remove the Emitters from the stars, this was done with a butane torch, heating the star from behind while tapping the star on the table until the emitter fell off (and then I re-tested the emitters).
Also note that the corners of the emitters were snipped off to isolate the top terminals (from the ones on the bottom which would otherwise short to the heatsink).
Wired the emitters in series and mounted on the heatsink with Arctic Alumina epoxy. Care had to be taken not to short the wires to the heatsink or the LED base since the emitters are a pain to solder. The optic was then placed over the LED's. In order to get the proper placement when I glued the emitters to the heatsink, I placed the optic on, then seated it on the emitters and then glued the emitters to the heatsink. Once the glue dried I removed the optic and soldered the wires (in series) to the leds.
Emitters on the heatsink and the optic in place, ready to go into the light.
I used a washer to raise the heatsink and optic to the correct height.
I disassembled the MagLite and removed the switch (remove the button cap and insert a small hex in the hole in the switch and unscrew a set screw at the opposite side, then the switch will fall out. Also remove the inside retaining ring if you wish.
Here is the disassembled switch module:
Holes need to be drilled in the switch housing to thread the input + and - and the +5V reference line from the Buckpuck:
The body of the Maglite was cut at the point after the switch where the checkering begins on the grip. The threads were also filed off the tailcap to allow it to insert into the tube:
This is the completed switch assembly with the input + (red) and – (black) and the +5V reference (yellow) shown going through the switch case. The +5V reference (yellow) is soldered to the terminal of the switch, on the other side of the switch the control (gray) is soldered to that terminal (not shown). There was a hole drilled in the center of the tailcap where a waterproof three-prong connector was mounted for the input + and – lines.
Here is the completed light. The switch was re-installed (I removed the terminal from the original negative terminal of the switch, so it is no longer an electrical contact (but mechanically holds the switch in position using the original set screw and nut. The Tailcap was glued and taped (I would not suggest over-doing the glue since you may need to take this apart later (electrical tape by itself works well). The Buckpuck sits between the switch and the head of the light and I soldered the output + and – lines to the wires connected to the LED's which were already attached to the heatsink and optics (and wired in series).
I used a cantilever scope mount with a RIS mount to connect the light to the bike (the bike mount is an RIS rail). The Maglite body is however slightly too big to fit the 30mm mount so it required quite a bit of filing down the inside of the mount (filed down to the point I encroached on the screw holes). This mount also had some QC issues so additional filing was required to get a tight fit on the rail. Once it was completed however it holds the light very secure. I also added a glow-in-the dark button cap which is questionably waterproof.
This is the RIS rail mount connected to the bike handlebar.
This is the completed light mounted on the bike:
This is the battery pack (I am still waiting on heat shrink tubing and a Pelican 1040 case to put it in). This is a 5C A123 pack built with cells from a Dewalt pack, making a 16v pack. As the LEDs need 3.7v x 4 LED's = 14.8v and adding the Buckpuck (estimated about 1.5v drop), this should be just about right. I have a Bantam BC6 charger which is able to charge and balance up to a 6C A123 pack which is the reason for the balance connector. Inside th pack is a 4.2 Amp polyswitch and a 70 degree C thermostat.
The big advantage to A123 cells from what I have read is that they are much safer than typical L-ion (they do not have runaway reactions). However these can put out some serious current so care must be taken in handling this pack. I tried to keep the terminals covered with tape when I was not working on them and in it's final configuration this pack will be sealed in heat shrink tubing. Also, NEVER cut two leads at the same time as this can cause a short and probably end up with a wire welded to your cutter and possibly much worse (I have read these cells can discharge at 50C for a few seconds).
I used the computer cable as the battery cable and am going to use some wire glands to get it into the Pelican case. The waterproof connectors were a great find for me. They are made by switchcraft and I have used them in several projects so far with good results. Even though the connectors are indexed, care still needs to be taken when plugging the light in. I used Deans connectors for the battery pack itself.
I do not have beam shots or run times yet, but the beam is very bright, so bright I don't think it would be wise to use it on the road unless it is pointed well downward. The head does get a bit warm, but I think it will be OK once I get some more thermal compound in the right places to spread the heat out. I have not yet charged the pack so I am not sure about the performance of the A123 cells in that regard but so far I like them.
Some things I wish I could find are:
A small and cheap battery monitor for a 6c pack.
An inexpensive and small protection circuit for a Life/A123 battery setup.
More Maglite heatsink options (there are many, but it take some research to find the right ones for the job). A simple AL slug with hole in the middle would work fine and should be cheap (heck I can even cut the slug to size and drill the hole).
A multi-size pack of heat shrink tube in various sizes (the big stuff) for making various packs.
Last edited by A123Powered; 04-07-2008 at 04:24 PM.
Re: Mag 4xCREE Bike Light with external A123 battery
The light was running too hot and was also too bright for riding on the road, so I installed a 5k ohm pot today. I did not want to give up my backlit switch however so I installed it in place of the existing switch. I just had to trim the inside of the switch housing and bore out the switch post hole a little and then wire it up to the buckpuck. Although it cannot be seen in these pics, I was able to retain the backlit switch using some clear silicone inside the switch cap. I may replace this with epoxy if it becomes too soft to turn, but so far it works OK.