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NiCd Battery Powered LED Lamp


xtp

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Bright white LEDs must be supplied with min. 2.9V (@about 0.5mA  ;D)

They certainly won't be bright at only 0.5mA! 20mA is usually used.
When you stepup the voltage then you also stepup the battery current.
The voltage stepup converter gets warm which wastes power that must also be supplied by the battery.

Ante recently posted these circuits. The 1st one regulates the stepped-up voltage.
http://elm-chan.org/works/led2/report.html
http://elm-chan.org/works/led1/report_e.html
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Stepping up the voltage increases the battery current due to the Law of Energy.
The two-cell Ni-Cad battery will be 2.5V over most of its life. If the LEDs need 8mA at 3V then they consume a power of 24mW, plus power for the step-up circuit.
24mW from the 2.5V battery will cause its current to be 24/2.5 = 9.6mA plus current for the step-up circuit. The current for the step-up circuit might be an additional 3.2mA for a total drain on the battery of 12.8mA. If the circuit is on continuously, 800mA/hr cells must be recharged every 2 days.

Use 2500mA/hr Ni-MH AA cells and the thingy will operate for more than a week before needing a recharge. Or you can increase the LED current for more brightness and recharge more often.

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But if the circuit is used only six hours a day then the batteries will have to be recharged only after a week ;D.
The step up circuit should be simple and compact, so the lamp will easily fit in a pocket.

Good, then you can use tiny 850mA/hr AAA Ni-MH cells. They are much smaller and lighter than AA Ni-Cad cells. ;D
Ni-Cads are obsolete and toxic. Energizer doesn't make them anymore. :'(
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I believe they still do, but they're probably no longer available to the general public. Nicad does have its advantages like being more abuse tollerant, longer life and higher discharge capcity.

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Most of my old Ni-Cads leaked or shorted so I've been using Ni-MH cells instead for a few years.

A metal crystal has probably grown accros the electrodes, you could possibly revive them by giving them a few >10A 1 second pulses to vapourise the crystal.

This won't happen with modern reflex battery chargers anyway as


The capacity of Ni-MH cells is much higher than Ni-Cads.

About double if I remember correctly, but this and their non toxicity are a the only advantages NiMH cells have.
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I have a lot of new NiCd batteries and I plan to use them.
NiMH batteries are smaller ;D, but they require a more complicated charger :P than the NiCd batteries.

You don't need a complicated charger unless you leave them charging for weeks, or need fast-charging.
Just charge them through a current-limiting resistor at their capacity/10 overnight, from a voltage source of 1.45V per cell in series.
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