Thursday, July 10, 2008

The motor, led, battery and charging circuit side of the LED Torch

Here is the half of the torch that holds the LEDs, rechargeabl the lithium ion battery, the charging circuit and the DC motor. The PCB is a good quality expoxy PCB. The lithium battery( green rimmed round object ) is a LIR2032 directly soldered to the PCB. A simple one transistor circuit with a zener diode charge the battery at a constant voltage of about 3.6V. Each LED is individually connected to the battery via a resistor. This prevents shorts on one LED blanking out the rest of the LED. The DC motor being used as a generator here is those common found in toy cars etc. The specs says that the torch should last 10 years with weekly used. Looking at it, the probable failure point would be the rechargebale lithium ion battery( unable to hold charge ), wear in the DC motor brushes, the nylon gears seems strong enough to handle the stress of hand winding. A simple modification would be to replace the rechargeable lithium ion battery with a 1Farad supercapacitor. The would allow greater charge recharge cyles and potentially longer operating life of the

The top picture shows the sub assemblies mounted on this half of the torch. The frame holding the DC motor, the PCB with the mounted LEDS, and the reflector.
The reflector plays a small role in focus the light from the LED into a wider spot, however most LED already has a mold lens build in, especially the green LEDs being use here to replace the white LEDs.

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