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Can I recharge button batteries with a series photodiodes

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I have a watch which doesnt need because of its own solar cell. There must be a solve with a solar cell. ( forgive my english..It is not my native language)
 
Hmm...Might work if u use several an u have very good wheather..I'd like to hear Philba' opinion but the size of the power source is beyond phesability.
 
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Ridiculous!
With a very bright light, a BPW34 photodiode supplies 0.365V open-circuit (no load) or a short-circuit current of 80uA. So you will need more than 8,562 photodiodes brightly lighted all the time to supply 5V at 50mA or twice as many to supply the circuit plus charge a battery.

Does anybody make lithium rechargable button cells? Will their charge supply 50mA for more than a few minutes?
You will need two cell phone batteries to power the thing for 12 hours a day, and a pretty big solar panel to power it for the other 12 hours and to charge the battery. It won't be small.
 
Photodiodes, you would need a bunch of them. Probably not the best choice if size is a factor. Have you measured the voltage/current of your photodiode? Maybe 0.4 volts in very bright sunlight, don't think the current is very high (never measured it myself). Just to get 6volts (you'll need more to charge), looking at about 15 (think you'll be using 2 X 3volt buttons).

Solarbotics.com is mostly about using small solar panels, like from calculators. Well worth a look, since they do amazing things with so little. But atleast you get a better idea of size and power you can expect.
 
Will I can get answer?.. Can I recharge button batteries with photodiodes such as BPW 34
The answer is NO.

Look at the data sheet. Each one will only produce 70uA at 1000 lux! You'd need so many that the guy would need more than 2 arms just to overcome the self discharge rate of the nicad battery, let alone charge it.
 
sure he can, with about 10K of them (don't people read posts before replying????).

as to the cpc1822. No, I don't think one would work as short circuit current is 50 uA (that's 1/1000 the current draw mentioned).

I have to say, the choice of a PIC at 25 mA (your numbers) is definitely not the best. Personally, I'd look at the TMS430 line which is engineered for super low power. Also, use of a transceiver seems overly agressive as well - do you really need 2 way? Though the transmit power is 12.5 mA I'd think you could get the peak current draw down to about 15 mA and using a 1% duty cycle, you could last a very long time even on a button cell.

low power engineering is pretty tricky.
 
philba said:
I have to say, the choice of a PIC at 25 mA (your numbers) is definitely not the best.

I would suspect that's NOT the PIC, but the surrounding circuitry - PIC's are pretty low consumption, and by sensible design can be VERY low.
 
No argument there. I still don't understand his design - a transceiver implies something pretty active which makes low power design more of a challenge (you have to listen). I'd figure out a way to make it transmit-only with a very low duty cycle.
 
The circuit will require 5 volts minmum, regardless of duty cycle. The photodiodes will still need to generate this, even if only microamps. It's still going to take a lot of them. If the draw is so small, why not just change the battery after a couple weeks...
 
that's an example of why I don't think it's well thought out. I'd run it at 3V or less.

by the way, I'm pretty sure the diode is a dead issue here...
 
philba said:
by the way, I'm pretty sure the diode is a dead issue here...
You mean, using 10,000 photodiodes to power and to charge a battery for this current-hungry circuit is a dead issue.
 
50mA is an awful lot of current for 24 hours each day, plus more for charging a battery. A bunch of AAA Ni-MH cells and a pretty big solar panel will work.
 
I will use 18 BPW 34...9 serial and 9 parallel..We will see..I will report if it was work or not. Thank you ...You are real friends
 
amerotke said:
I will use 18 BPW 34...9 serial and 9 parallel..We will see..I will report if it was work or not.
I wonder what they will produce with a very bright light.
18 in series make 3.15V without any current.
2 in parallel make 160uA into a short.
Maybe 18 will produce 1.5V at 80uA?
 
They will charge button batteries. Batteries will let circuit work. Circuit will work one or two millisecond per minute. Photodiodes must keep alive these batteries.
 
That is a nice short duty-cycle. Photo-diodes will work fine to charge the battery with only 2uA continuously.
 
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