Check-up from the neck up

Discussion in 'The Projects Forum' started by bisctboy, May 20, 2009.

  1. bisctboy

    Thread Starter Member

    Nov 3, 2008
    My Project
    I am trying to build a Li Ion solar charger for my portable electronic devices. The devices include a handheld Garmin GPS, iPod, and Blackberry. My goal is to have a lithium ion battery (roughly 1500mah) in my circuit that these devices can charge from even while I am charging the battery through two 4.5v/90ma solar cells connected in parallel. The output of the solar cells should be 4.5v/180ma but in the real world my solar cells output about 4.3v and 140ma.

    I am attempting to meld 2 schematics together that I found on the internet for my solution. The first is a schematic supplied from the DIY version of the Minty Boost and it includes a 5v boost converter. The second is from Sparkfun’s LiPoly/LiIon charger and it includes a Maxim 1555. My though process behind the need to combine the two is that Minty Boost is meant for AA alkaline batteries and I want to convert it to a rechargeable Li Ion setup which would require something like Sparkfun’s schematic

    My plan is to combine the two schematics from both products into one DIY PCB rather than connect the two separate products somehow.

    My Assumptions
    The IC in Li Ion charger schematic provided by Sparkfun has the Maxim 1555 as the “center piece”. I’m taking the spec sheet on the Maxim 1555 at face value when it states that it will allow charge from the solar cell even while the battery is recharging one of my devices. Furthermore, the schematic shows a USB power input and wallwort power input and I am assuming I can leave those out in my project and just opt for a solar cell power input.

    The power for the Minty Boost comes from two AA alkaline batteries. I am assuming that replacing these with a 3.7v Li Ion is an acceptable alternative for the given circuitry on the schematic.

    My Questions
    1) Do I even need the Li Ion circuitry if my solar cell puts out so little current?
    2) Is there an easier way to do what I want to accomplish?
    3) Is there better/cheaper alternative IC’s and components than I have described?
    4) If I had to choose between learning LT Spice IV and Eagle, which one should I learn?

    Yep, I’m a complete newbie, but I purchased an Arduino and I am having fun with the circuits and thought I’d try something else for a change. Please poke holes and give suggestions to the above. Basically, I need a "check-up from the neck up" on my project.

    Thanks in advance!
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    I am not aware of any. You've done well on your initial investigations.
    Again, you've done well and found a practical & economic solution.
    Both. LT Spice won't draw PCB art by itself, and Eagle won't simulate. Oh, if you HAD to choose, go with Eagle. You can always run your circuit analysis manually like we did in the good old days. ;)
  3. bisctboy

    Thread Starter Member

    Nov 3, 2008
    Wow...thank you.