Simple single cell Li-Ion battery charger utilizing NCP1835

Discussion in 'The Projects Forum' started by wirednuts, Nov 13, 2011.

  1. wirednuts

    wirednuts Thread Starter New Member

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    its a chip made by On semiconductor and theres still a few left at mouser.

    i originally planned on just modifying the existing charger chips inside a cheap charger, but i then figured for $2 i could replace it with a much better solution. im getting a few external chargers that are molded to my cell phone battery, (touch pro 2), and ill remove the internal 350ma charger and replace it with this circuit which is 1000ma.

    [​IMG]
    Features
    • Integrated Voltage and Current Regulation
    • No External MOSFET, Sense Resistor or Blocking Diode Required
    • Charge Current Thermal Foldback
    • Integrated Pre−charge Current for Conditioning Deeply Discharged
    Battery
    • Integrated End−of−Charge (EOC) Detection
    • 1% Voltage Regulation
    • 4.2 V or 4.242 V Regulated Output Voltage
    • Regulation Maintained without a Battery Present
    • Programmable Full Charge Current 300 − 1000 mA
    • Open−Drain Charger Status and Fault Alert Flags
    • 2.8 V Output for AC Present Indication and Powering Charging
    Subsystems
    • Minimum Input Voltage of 2.4 V Allows Use of Current Limited
    Adapters
    • Automatically Recharging if Battery Voltage Drops after Charging
    Cycle is Completed
    • Low Profile 3x3 mm DFN Package
    • Pb−Free Packages are Available


    http://www.onsemi.com/pub_link/Collateral/NCP1835-D.PDF

    as you can see it doesn't take many external parts to make it work, and i guess you can hook it to a microprocessor too for more control. i just want something simple, and after much searching through datasheets, i think this one is the best value.

    love to hear any opinions... but the only real question i have is what specific capacitor would be best for the timing circuit?
  2. bertus

    bertus Administrator Staff Member

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    Last edited: Nov 13, 2011
  3. wirednuts

    wirednuts Thread Starter New Member

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    this is for 1500mah batteries, which should be safe to charge at 1a. i will build this so the charger heatsinks close to the battery, that way if the charger or battery gets too warm it will cycle off.

    i did not mean what value of capacitor, but if there was a specific kind (ceramic?) that is best for this timer use.

    edit- thanks though, looking at things closer i see it would make sense to limit the timer to 140min and change the max charging current to 800ma. i like running things a little under their rating.
    Last edited: Nov 13, 2011
  4. bountyhunter

    bountyhunter Well-Known Member

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    You want a ceramic type "NPO" which is temp stable for an accurate timer. You can also use a poly film type cap.
  5. wirednuts

    wirednuts Thread Starter New Member

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    well right before you posted that, i of course already placed an order with some basic xr7 ceramic capacitors. they should be fine though, the timeout period is a last-resort fail safe anyway, accuracy is not that important here. i also noticed the variations with temperature are plenty acceptable for my application too....

    pretty excited, i have enough parts coming to make 5 of these. if all goes well, i will have one in my room, in my truck, one in my tool bag and one in my laptop bag. i have 2 more batteries coming too for a total of 4... because i genuinely dont like plugging a cord into my phone to recharge it. its much nicer to just pop the battery and stick a fresh one in. plus, this external charger will charge batteries within an hour, not the normal 3 it takes when its in your phone and running all your apps. best part is, this charging chip maintains batteries while plugged in... so i can leave batteries in the charger indefinitely without worry... hopefully:D....
  6. wirednuts

    wirednuts Thread Starter New Member

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    ok i guess i forgot to read the part in the datasheet where it says the NCP1835 is too small for any practical purposes...

    [​IMG]

    should i just give up now? is there any possible way i can solder to this chip by hand?
  7. wayneh

    wayneh AAC Fanatic!

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    No and no, IMHO. Live and learn, huh?

    Don't give up yet - there are things to allow using surface mount components in thru-hole boards. No idea if anything is available for a chip THAT small, but worth a look. And somebody here might have ideas for you. I can say with 100% confidence that I would have zero chance of soldering that sucker. I'd need dissecting microscope to just see the thing.
  8. wirednuts

    wirednuts Thread Starter New Member

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    thats pretty much what i thought.

    it seems that the only way this is gonna happen is by using soldering paste and a heat gun.

    problem is, i dont have a circuit board to stick this thing on. all the tutorials on how to solder these kind of chips show them going onto a circuit board custom made for that chip.

    im not looking to make a circuit board for such a simple circuit... and even better is i cannot find any through-hole li-ion IC's like this one. i know they exist, there are shitty ones in these cheap chargers that im trying to mod. if the damn chinese would just put datasheets out for their shitty chips they make, i could probably just mod those circuits to boost the power output a bit (im sure their current is controlled by a resistor just like most others, yet im not in the mood to guess what does what, not with a lithium charger circuit anyway)

    this chip was obviously made for a cellphone...
  9. wirednuts

    wirednuts Thread Starter New Member

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    ARGH you know what, this is really frustrating because its not microscopic small... i can see it.. the pins, they are right there. hello pins just waiting to be soldered. hows it goin? i see you right there in plain sight, and i have no idea how to burn your pads.... this isnt over.
  10. Georacer

    Georacer Moderator Staff Member

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    Why don't you buy some solder paste and bake it?
  11. wirednuts

    wirednuts Thread Starter New Member

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    bake it to what? i dont have a circuit board to put this on, i thought i bought a tiny bit larger chip that i might be able to directly solder some small wires to...

    maybe if i somehow laid single strands of copper and taped them down, then tried to flow solder the chip to the wires in perfect placement.... ugh this sucks
  12. Georacer

    Georacer Moderator Staff Member

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    For fine work, this is what I usually do. I coat both surfaces with solder and then tap them for an instant with a soldering iron. Considering that my iron is pretty large for that kind of work, the result is always pale and blobby, but I don't have any other choice, do I?

    Would it be possible for you to buy a copper board, cut a small bit and carve pads for your IC? Like a small DIY board. You could then use solder paste and have larger pads for your wires to be soldered onto. It would need a steady hand, though.
  13. wirednuts

    wirednuts Thread Starter New Member

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    thats exactly what i was thinking. if i got a bank pcb with solid copper on one side.... i dont know where to get that though. the bank pcb's i have are all through hole, and i looked at trying to scratch some circuit paths but it wont work, the holes mess it up. also, would i have to fill in the scratches with something? i dont want solder to bridge everything together, and i know normal pcb boards have coatings to protect that.

    i would need a big magnifying glass and a new sharp exacto blade... and a bowl of marijuana. i can get all that, so i just need to find a solid copper pcb board

    something else does bother me though... these pins are SO small, it doesnt even seem like theres enough metal there to handle 5 watts of power at that point... but i suppose thats why these stupid chips arent even smaller then they are :)
  14. wirednuts

    wirednuts Thread Starter New Member

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  15. wirednuts

    wirednuts Thread Starter New Member

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    ok so i think i finally found a solution. for $20 these guys will make and print a dozen of single sided custom boards for me- http://www.futurlec.com/PCBService.shtml

    1 week process time, and can use a variety of pcb layout software.

    my only question right now- do i need to have them apply solder mask? will it matter when i go to paste solder that smd chip?
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