This thing was 99p. I thought, wow, that's a big solar panel and three LEDs for 99p. How can they do that?
A simple dissection shows that the circuit is very simple. There's a lithium battery, CR2016, 3V. Famed for its rechargeable nature. eek A PCB switch mounted on a small piece of PCB. And three LEDs in parallel... no limiting resistor, although not usually required as the lithium cells have such a high ESR that they limit the current sufficiently.
But wait, how does the solar cell come into it?
Well, it doesn't... or at least, nothing is connected to the panel. And in fact, the torch does not work with the battery disconnected.
So, I thought, why would they bother with such a large solar panel? Those panels would be quite expensive - about £3 to £5 each - and there's no way they could sell these at 99p. Then I looked carefully, and I noticed something didn't look right with the cell. There were these red wires, running out of line with the electrode wires. Also, the cell has several holes in it. So it's basically for show.
I measured the cell as putting out less than 1mA short circuit, and about 2.2V open circuit, so it's pretty dead.
Now I'm not that bothered, after all it was only 99p but it really seems shady (puntended) to me to sell these as solar powered!
A simple dissection shows that the circuit is very simple. There's a lithium battery, CR2016, 3V. Famed for its rechargeable nature. eek A PCB switch mounted on a small piece of PCB. And three LEDs in parallel... no limiting resistor, although not usually required as the lithium cells have such a high ESR that they limit the current sufficiently.
But wait, how does the solar cell come into it?
Well, it doesn't... or at least, nothing is connected to the panel. And in fact, the torch does not work with the battery disconnected.
So, I thought, why would they bother with such a large solar panel? Those panels would be quite expensive - about £3 to £5 each - and there's no way they could sell these at 99p. Then I looked carefully, and I noticed something didn't look right with the cell. There were these red wires, running out of line with the electrode wires. Also, the cell has several holes in it. So it's basically for show.
I measured the cell as putting out less than 1mA short circuit, and about 2.2V open circuit, so it's pretty dead.
Now I'm not that bothered, after all it was only 99p but it really seems shady (puntended) to me to sell these as solar powered!
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