Hi everybody,
as the arduino-forum is my common forum I'm asking here:
A friend of mine uses a tiny solarcharger modul 2V /100 mA with a singlecell 1,2V/600 mAh NiMH-battery for is gardenmodelrailway to light up some modelhouses etc.
This tiny modul has a 4pin chip in a small TO92 housing. This thing is able to light up a white LED from the single-cell NiMH-battery. At first glance I was very astonished as even a red LED has a forward-voltage of 1,6V. It turned out that the 4pin-chip is some kind of micro-step-up-circuit for a very small current of 5 mA. On the oscilliscope I measured outputvoltage is a168 kHz with small 9V-spikes.
Ah ! that's the trick! As the circuit has a 15 Ohm-resistor in series the current is limited and with connecting an LED the voltage went down but the LED lights up.
Now he wants to use this modul for a lighthouse (light-"tower") with blinking LEDs.
The blinking LEDs need 5V. But simply connecting a DC-DC-step-up-modul does not work.
Of course not as such a DC-DC-step-up-module will need more than 5 mA and expects not small 9V spikes with 168 kHz as input.
So now a different simple charger-circuit is needed. It does not have to be high-efficient as everything is only about 2 or 4 small blinking LEDs. The solarmodule could be easily changed to another one with 5V or 6V current 100 mA to 200 mA.
I don't want to use a Lithium-polymere-battery as they can catch fire when overcharged.
So I'm looking for a small charger-modul or a quite simple charger-circuit for a single-cell LiFePo4-battery (3,2V)
or 3x1,2V = 3,6V NiMH-batteries which can't catch fire.
Again: I want to emphasize efficiency is not important.
Does anybody know of a simple charging circuit?
stop charging at 3,2V switch off supply at 2,6V
Or in case of 3x 1,2V NiMH stop charging at 3,9V switch off at 3V
best regards Stefan