1. AC Question's Avatar
    Just Wondering, I've noticed that my phone charges really quickly up to 90%, but then, it slows down, and takes much longer for the last 10%.
    Has anyone else had this too?
    01-09-2017 12:46 PM
  2. Mycrossover's Avatar
    Just Wondering, I've noticed that my phone charges really quickly up to 90%, but then, it slows down, and takes much longer for the last 10%.
    Has anyone else had this too?
    I bought one of those usb, in line voltage and current monitors (under 3 bucks on ebay). I charge around 1.7- 1 8 amps for most of the charge and than the current drops way off for the last 10%. It is the battery that controls charge current. The charger is a rather poorly regulated 5 volt power supply. It remains at 5 volts even after the current drops. The overcharge protection is in the battery and apparantly does not kick in at the last moment but starts to reduce current as the battery approaches full charge. Over charged lithium batteries catch fire and you don't want to risk coming right up to the limit at full charge current.
    01-09-2017 01:35 PM
  3. B. Diddy's Avatar
    It's normal for the charging curve to level off as you approach 100%. See this article: Charging Lithium-Ion Batteries – Battery University. (Battery University is a great informative site in general.)
    Morty2264 likes this.
    01-09-2017 03:32 PM
  4. Morty2264's Avatar
    It's normal for the charging curve to level off as you approach 100%. See this article: Charging Lithium-Ion Batteries – Battery University. (Battery University is a great informative site in general.)
    Awesome link! Thanks for sharing it!
    B. Diddy likes this.
    01-09-2017 03:49 PM
  5. Mycrossover's Avatar
    It's normal for the charging curve to level off as you approach 100%. See this article: Charging Lithium-Ion Batteries – Battery University. (Battery University is a great informative site in general.)
    You are not reading what the articke says, correctly.. The graph shows constant current and saturation current. This refers to battery performance on a multi stage charger.Most phone chargers are not constant current, they are barely constant voltage. They are incapable of of monitoring battery state of charge. You only have to monitor the charger voltage to see it puts out a poorly regulated 5 volts all the time. If you had ever worked with lithium cells you would know that they are never used without protective circuitry to prevent them from damage from over charging and over discharging. What do you think all those lithium battery fires are all about. With a constant voltage charge, the current will drop with any battery as the battery voltage rises to meet the charger voltage. That article references the use if smart chargers and not the simple charger that comes with your phone. Any battery chemistry can be forced into a saturated state above it's nominal voltage but every chemistry has a maxumum normal voltage based on that chemistry. That is the reason that car batteries are allowed to rest afrer charging before voltage is checked. It allows the top charge to bleed off.
    01-10-2017 01:14 AM
  6. B. Diddy's Avatar
    I see -- sorry for the misunderstanding (medicine is my field, not physics). I was also looking at this site: Li-ion battery charging. So the leveling-off curve that I was referring to was the constant voltage stage. The article seems to imply that most phone chargers do in fact charge via this constant current to constant voltage sequence -- is that incorrect?
    01-10-2017 01:54 AM
  7. Mycrossover's Avatar
    I see -- sorry for the misunderstanding (medicine is my field, not physics). I was also looking at this site: Li-ion battery charging. So the leveling-off curve that I was referring to was the constant voltage stage. The article seems to imply that most phone chargers do in fact charge via this constant current to constant voltage sequence -- is that incorrect?
    Yes. They are just little 5 volt power supplies with the exception of the fast charge ones that detect whether the battery can handle two stage charge that starts out at a very high rate. For 3 bucks on ebay you can insert a little voltmeter and ammeter module between the charger and the the usb cable and watch the voltmeter fluctuate plus or minus several tenths around 5 volts regardless of big changes on the ammeter. No apology required and I am sorry if I sounded a little snarky. Sime devices charge at a higher rate and as ling as the charger is good for more rhan the device you are maxed out. My phone will charge at 1 8 Amps but my blue tooth speaker will not draw more than 1 Amp on the same charger. I can use my 2 1 Amp phone charger for either but the 1Amp charger that came with the speaker cannot charge the phone faster than than 1 Amp
    01-10-2017 03:20 AM

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