I came across a pair of branded 10W MR11 halogen bulbs from a local store. The bulbs have a flood pattern and have glass covers similar to the MR16 that I earlier used. MR11's are less efficient than MR16's due to their smaller reflector size. On average, a 10 Watt MR11 halogen will yield about 190 lumens at 12 volts. The same bulb will yield 265-350 lumens when over volted to 13.2-14.4 volts respectively. In comparison, a 10 Watt MR16 halogen will have about 400 lumens at 12 volts.
Despite having a lumen output of less than 50% for the same power consumption, the MR11 has the advantage of being significantly smaller than the MR16. Furthermore, 10 watts will also put out a lot less heat than the 20 watt MR16. This time, I decided to use mostly plastics and PVC for construction.
(Proof of concept: I ran a single MR11 @ 12 volts indoors for almost 3 hours without any detrimental effect on the housing).
Parts List:
2 pcs 10 Watt MR11 halogen bulbs with glass cover (35 deg flood beam)
2 pcs 1-3/8 x 2" schedule 40 PVC couplings (non-threaded)
2 pcs SPST rocker switches (recycled from PC power supplies)
1 small tube GE silicon II clear adhesive/sealant
assorted bits and pieces of pvc/abs/plastic
cyanoacrylate based glue (super glue, gorilla glue or equivalent)
assorted lengths of 16 gauge wire (14 gauge max, 18 gauge min thickness)
1 cheap dollar store bike light with handlebar mount
18" desktop computer power cord (leftover from previous project)
10" x 3/4" pvc pipe (any color / preferably thin walled)
heat resistant black paint
The two pvc couplings were bonded together in a side-by-side configuration. Cyanoacrylate (CA) glue was used instead of pvc cement since I was going to glue different plastics together. A backplate cover was constructed using two layers of ABS plastic (recycled from a computer case). This will cover the back end of the PVC couplings as well as provide a mounting location for switches and labels.
After cutting two small rectangular holes on the backplate for the rocker switches, additional holes were made to accomodate wires and connectors. (The location of each switch and the exit hole for the power wire is a matter of preference).
All power wires and connections were connected and assembled inside the right hand side PVC housing. Due to limited space, I soldered the power wires directly to the MR11 pins. A generous bead of GE silicone II was placed near the front end of the PVC couplings and after allowing this to dry for about a hour, more silicone was placed around each halogen bulb. The bulbs were then sealed and pressed flush against the couplings and allowed to dry for at least a day.
To mount the light assembly on the handlebar, I cut away the slider and receiver portion from a dollar store bought bike light. The slider part was mounted at a 30 degree angle and then then reinforced with additional ABS plastic. Everything was painted with heat resistant black paint. The textured pattern for the paint was done intentionally.
The reverse 30 degree configuration also meant that the receiver part would be pointing downward and away from the rider. This assures that even if the locking part of the mount fails, the light will stay in place. Furthermore, this configuration positions the switches at a better angle for rider access.
Bike Light version 2 is designed for single bulb operation. Ten watts should be sufficient for normal use due to its wider beam pattern. The other bulb is more of a redundancy feature i.e. a secondary light should the first one fail. Both can run simultaneously but with a drastic reduction in runtime.
Single Mode
Dual mode
Beam shots
Single Beam
Dual Beam
Based on the the pictures above, there are no noticeable increase in brightness or light dispersion. This is because the lefthand light is actually angled a bit more inwards to prevent blinding incoming traffic. In contrast, the picture below compares the beamshot from the 20-watt single beam Bike light Version 1.1 (spice jar light).
Bike Light version 2 is also designed to function using different power sources. It can utilize the original harness from version 1.1 and run on the existing 12V 5Ah sealed lead acid battery, an existing 14.4V 1.4Ah power tool NiCD pack, and a 10 to 12 cell NiMH battery pack. It can also use a shorter harness and obtain power from a 3 or 4 cell 18650 lithium pack. The lithium pack is much lighter than the SLA and could be mounted inside a small pouch and attached to the handlebar stem.
(The Force decal mimics the large sticker on the bike's downtube. This smaller version is just printed on plain paper, covered with tape and glued to the housing. Everything is then covered with clear acrylic nail polish).
Pouch can hold a 3 or 4 cell lithium pack
DIY 18650 lithium holders in a 3-cell and 4-cell configuration
Based on the chart above, the THEORETICAL runtime from a 2200 mAh 3 or 4 cell pack should be about 3 hours when using a single 10W halogen. In actual use, expect about 1.5-2.0 hours continous operation from these USED and UNPROTECTED 18650 cells.
(Samsungs were tested @ 10 watts and produced usable light up to 2.5 hours. The Sony and some Toshiba cells were good up to 2 hours. Four of the 9 Toshiba cells lost charge rapidly yielding only about an hour of usable light).
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Sidebar:
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Protected 18650 Lithium cells have a maximum termination charge of about 4.2 volts and a minimum final voltage of 3.7 volts. A cell is considered fully discharged at this state. A smart lithium ion charger senses these voltage limits and safely charges a cell. Most lithium batteries have a protection circuit (either per cell or per battery pack). Having a protection circuit prevents the cell from draining way beyond 3.7 volts or discharging too fast. Individual cells are usually protected up to 2A. Multiple cell packs can be protected with commercially avaialable PCB's between 4-5A.
An assembled pack of 3 cells would therefore have a usable charge between 11.1-12.6 volts. A 4-pack will have 14.8-16.8 volts. A commercially assembled pack will have the convenience of being charged as a single unit as well as be properly protected. The disadvantage of a built pack is that most cheap commerically available chargers (purchased online for under $25) will eventually destroy the cells. Additionally, if a single cell dies in a pack, replacing it usually means cutting open the pack.
Using individual cells means having to charge each cell independently, but since I'm only using 3 or 4 cells at any given time, charge time won't be an issue.
I obtained several used 18650 lithium cells from 3 laptops. After disassembling the packs, I ended up with 25 unprotected cells. Each cell is originally rated at 2200 mAh but the actual capacities vary between manufacturers. The 16 cells that came off an Acer (SF.US18650GR) and Samsung laptop (ICR18650-22B) seem to have real 2200 mAh capacities. The remaining 9 from a Toshiba laptop (LR1865AF) seem to be closer to 1800 mAh. The first two are probably best suited for single (3S and 4S) configurations while the latter will probably be better in a combined single-parallel pack (4S1P, 4S2P, 3S3P).
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I made two DIY battery holders using 3/4 inch thin walled PVC pipe. The positive terminals were made from coiled copper wire and the negative spring contacts came from the recycled springs from the dollar store bike light that donated the handlebar mounting clamps. A velcro binding strap wraps around each cell pack to assure that all the cells stay in position.
Eventually I will be making either a 4S2P 14.8V 3600mAh pack or a 3S3P 11.1V 5400mAh pack for extended runtime from the Toshiba cells.
Project cost:
MR11 bulbs 2 pcs - $5
PVC couplings 2 pcs - $3
GE Silicone II tube - $3
Donor Bike Light - $1
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Total = CAN$12
All the other components I already had on hand or recycled from existing parts.
Finally, here is a comparison between the Version 1.1 and Version 2. Version 1.5 will not have a significant difference from Version 1.1. The housing and all other components will be the same and only the emitter will be different.
