Riced Dynamo flashlight

On our van trip across the country my aunt and uncle gave us two hand crank (dynamo) LED flashlights which are really useful to keep in the van. The self-charging nature of the flashlights are very nice, in that we can leave them in the van and just wind them up when we need light. Unfortunately, one of the flashlights started to dim and refused to hold a charge. When I got home and opened it up, I found that the rechargeable Li-Ion coin cell inside had died. It originally used a 2032 coin cell rated at 40mAh

Dynamo flashlight opened

Once I had it open, I decided I may as well fix it, and if I was going to be replacing the battery I may as well buy a bigger one (or two) and give the flashlight extra storage capacity. I purchased two LR2450 button cell batteries (which are slightly larger, but rated at 120mAh capacity). The two of them together provide 240mAh capacity (6 times more than stock). 

New Batteries

Seeing as how I was increasing the battery capacity, I decided I could also replace two of the LED's in the flashlight (the stock LED's draw 12mA) with 3w luxeon modules. The flashlight has a two way switch that has a low power (center LED only) and high power (all three LED's) mode, so I replace the two outside LED's to make a super high-power mode. These LEDs draws 85mA each when I bypass the current limiting diode, or approximately 0.30 watts each. This is 10% of the rated capacity of the 3W led, so I didn't feel too bad about not adding a heatsync to them.

Replacement LED’s Bypassed Current Limiting Resistors Before and After light comparisons

Above you can see  the new LED's (plus wires replacing the current limiting resistors) and a side-by-side comparison between the non-modified (on the left) and my riced  version (right). However, after looking up the maximum recommended current draw for the LR2450 cells (35mA each), I decided to add a 1 ohm current limiting resistor on each LED (limiting them to 35mA each) so I wouldn't risk overheating the li-ion cells. 


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