Jee Labs Talk

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1. powerbook
   

   Hi Jean Claude,

   I see today on your blog that you will connect an Solar Cell to an JeeNode with Lipo Cell...
   What kind of chip you will use to drive the LiPo charging in good and safe condition ?

   I was ordered solar cell from Futurlec with the same idea.. connect an Solar Cell to a JeeNode ;-)
   I was find lot's of drawing to connect a solar cell to NiCd or Nimh battery, the major problem there not a "over charge circuit protection" on them !

   I will try to use an zener diode and Fet transistor to "cut" the charging process if the cells are fully charged... hope find a simple and good solution (but i'm not confortable with analogic circuit diagram ;-)).

   If you have link or drawing of a safe solar cell charger... could you share them ?

   Thank you.

   Powerbook.

   Posted 02/07/2009 07:03:02

2. jcw
   

   Right now I'm using a solar cell which can only supply 4.5V @ 35mA at best. With a diode, that's 3.9V, so I think it cannot overcharge the 20 mAH cell I'm using.

   For more sophisticated cases, I'd use the MAX1555 charger. Might be an idea to include them in some future JeeNode.

   The other way to go, if power usage is really low is to use a super-capacitor. That can't be overcharged: solar cell -> diode -> supercap -> voltage regulator.

   Posted 02/07/2009 09:43:38

3. powerbook
   

   Lipo have a particular charge mode, it's not only an constant current charging mode.
   Solar panel are "constant current" generator, great for "direct" charge of Nimh or Nicd cells, but for Lipo...
   You could easy view if your cell is damaged (over charged) after one week or month, Lipo become puffy if you take too much current on it or if they are overcharged ;-)

   I will try to simulate my idea (solar Nimh charge with cut before over charge) this week, i hope find the Futurlec parcel (and JeeNode kits too) in my letterbox today !

   Posted 02/07/2009 14:31:41

4. jcw
   

   Yes, I'm aware of this. But if the solar cell generates at most 4.5V and the diode drop is 0.6, doesn't that mean that it can never charge a LiPo fully? At best it'll charge it halfway and then the current will stop as the cell voltage reaches 3.9V?

   I have no experience with LiPo's, I must admit. Just looking for a simple keep-it-more-or-less-charged-via-solar circuit...

   Posted 02/07/2009 16:53:32

5. seaton
   

   I did a bit of investigating with the LIPO cells when I was doing my solar powered widget (http://tiny.cc/HTtiv) as I originally wanted to use them. However the chemistry of the LIPO cells require a constant voltage to allow charging, which rules out trickle charging.

   I'd be interested to see your results when you get it up and running.

   Posted 03/07/2009 01:25:44

6. seaton
   

   I found this article today which may be of some use to you in charging a LIPO from solar.

   Stephen...

   Posted 09/09/2009 01:58:00

7. jcw
   

   Thanks - good info. I had shelved my project with the intention to either switch to a small NiMH battery or to put a MAX1555 regulator between the solar celll and the LiPo battery. We'll see...

   Posted 09/09/2009 09:21:30

8. mak6
   

   Hello Jean-Claude,

   are there any new experiences with Solar Cell and MAX1555 ?
   I want to use a Solar Cell in combination with MAX1811.

   Solar Cell ---- MAX1811 ----- LI-Ion

   Thanks,
   MAK6

   Posted 03/02/2010 07:19:09

9. jcw
   

   No, sorry - haven't gotten any news to report there so far.

   Posted 03/02/2010 16:32:20

10. jcw
    

    Just to follow up - the JeeNode USB v3 has an on-board MAX1555 now. So if you're willing to hack a few wires to the proper pins (sorry, no pads for that), then it ought to work.

    Posted 01/06/2010 12:09:57