Thanks to everyone who replied! I have found in replies to my mail many useful suggestions and Ideas. Regards Marco ----- Original Message ----- From: "Peter L. Peres" To: Sent: 1 marzo, 2002 18.56 Subject: [EE]: mini solar charging system > >Hi all, I'm thinking to an "essential" solar-charging system for a > >prototype of a "very remote" meteo-station . Average current consumption > >of the logger with all sensors is little, about 100-150 uA, so a > >possible solution can be a very little solar cell recharging a pack of 3 > >or 4 NI-CD cells (AA type). I have tested with a small (1" x 3") solar > >cell from a toy and I have measured about 40 milliamp. out in direct > >sunlight. I'm not an electronics expert but I suspect that this current > >is too high when the cells are full charged and a regulator will be > >mandatory (or I'm wrong?). I have read on PICList a lot of e-mails about > >a solar-charging system some days ago, but it seems a bit excessive for > >my use. Can anyone suggest me a simple and rugged solution for > >regulator? > > If you use NiCd and not MiMH then you can leave a trickle charge current > of 1/50C safely (this is 10mA for 500mAh cells - BUT consult the > manufacturer's data sheets!). > > The easiest way to regulate the charge from a current source (like solar > cells) is to put a parallel voltage limiter in parallel with the battery > being charged. Try to use a superdiode as a first start (using a > darlington transistor for 40mA). There are more elaborate schemes that > account for the temperature and other factors. Do not forget to add a > diode between the solar cell and the battery. > > Another very simple low current charger is a JFET and a resistor as > constant current source in series with the solar cell the diode (see > above) and the battery. This sets the max. charge current directly but may > cause the battery voltage to increase too much for your circuit when the > battery is fully charged. You can use it in combination with the > superdiode above to avoid this. > > These circuits were tried by me many years ago on NiCd button cells (Varta > 50mAh) using amorphous solar cells. The circuits were used to power clocks > and humidity (dew)/freeze alarms. They work very well. Set the superdiode > knee point to the highest voltage your circuit or battery will withstand > (I set to charged battery + 0.3V afair). I used 4.8V and 6V (4 or 5 > batteries) and CMOS 4000 series 'logic'. > > hope this helps, > > Peter > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics