Understanding How USB Charger Works

Discussion in 'Off Topic' started by NetBrakr, Oct 15, 2014.

  1. NetBrakr

    NetBrakr Gone With The Wind

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    I know this thread goes somewhere other then OT, but it's universal thing.

    Anyway, I just received my EZOPower 15W/3.1A (MAX) Dual USB Wall Charger.

    Now of course, I have other USB chargers by Samsung, 1A & 2A.

    If I charge my phone, SII (1200mAh battery) w/ the 3.1A charger, would the battery completely charged under 1 hour? Or it doesn't matter, it will just it sweet time charging?

    Also does the USB chargers ramp it to w/e the max Amp once it plug in? Or does it usually do slow charge at first then building up to max Amp?

    Does the wattage really matter?

    I was thinking to get the Anker 20w/4A Dual USB Wall charger. But it was backorder.

    Thanks guys.
     
  2. SGosnell

    SGosnell (retired) Palm Pilot

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    The phone will use as much amperage as it needs and is designed for, provided the charger can provide it. Higher amperage chargers don't charge any faster, they just won't burn up from the current draw of the phone. The amperage of the charger only matters if it's too small for the device being charged, in which case they can fail. Hooking up a 1000 Watt charger won't hurt, but it won't help, either. Use something designed for your phone, providing the recommended wattage or higher. If you want faster charge, increase the voltage, but that can destroy your battery.
     
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  3. NetBrakr

    NetBrakr Gone With The Wind

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    Thanks SG.

    I guess this is the same with power banks, huh?

    Power banks normally doesn't comes with a charger (at least from what I have already purchased).
     
  4. raspabalsa

    raspabalsa Brain stuck BogoMipping

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    Actually, the "USB charger" is just a constant voltage power supply. This means that, as long as the load connected to the "charger" does not exceed its amperage rating, then the power supply will mantain a constant 5V supply. This means the USB charger does not ramp the amperage up - it does not have the circuitry to do so.

    The real battery charger is inside the phone, tablet, or laptop (or any other device with rechargeable Li-Ion or Li-Poly batteries). This charger is the one that measures the battery's charge level, voltage, temperature, and its programmed to deliver a certain charging profile, that for Li-Poly batteries is called a "constant current - constant voltage" profile. During the first phase the charger delivers a constant current to the battery, so it can quickly charge it within its amperage limits. Once the battery reaches a certain charge state (around 90%) the charger switches to second phase, where it mantains a constant voltage, and delivers a decreasing current to the battery for the remaining charging time. The charger adjust the charging profile according to the external power supply, and this is why your phone takes longer to charge if you use a USB charger with lower amperage rating than your phone requires, because it will use a lower current during the constant current phase.

    More recent chargers take into account the battery's temperature, and vary the amperage accordingly to avoid overheating the battery. Most (if not all) laptops have this control, but it's become increasingly common in smartphones, especially on those with larger batteries and/or "fast charge" features.

    Only in the sense Stan said above. For a given wattage you can calculate the amperage dividing power by voltage (this simple formula is for DC power only). A 20W, 5V charger gives you 4 Amps maximum. But check the charger's manual, because its usual for chargers with multiple USB ports to have one high amperage port and another low amperage port.
    Quite similar, but you also have to check the power bank's rating to charge its battery. Then you should get a USB charger capable of delivering said amperage to the bank. I have a 2A USB charger for my Xperia Z1, and my 8600 mAH power bank requires 1A to charge, so I can use the same USB charger for the bank and Z1. The bank has one 2A port and one 1A port. On the 1A port my phone takes much longer to charge than on the 2A port.
     
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  5. jigwashere

    jigwashere Mobile Deity

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  6. NetBrakr

    NetBrakr Gone With The Wind

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    Raspy: Thanks for the detail explanation So if I charge my phone with my tablet's 2A charger, the phone will only go 1A cause that's design to do. My power bank said on the back, 1A input, so it only goes 1A charging.

    jig: Thanks jig for the tip, I guess I would need to get a fatter USB cable.
     
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  7. r0k

    r0k Dazed

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    I'm not sure that is entirely true. It depends on the phone. I know if I connect one of my iThings to a 2A charger, they charge a lot faster so perhaps Apple has designed recent iThings to exceed the standard 1A. I know this worked for my iPad which of course is expected but it also worked for my iPhone 5 and for my iPhone 6. This is why I went on Amazon and bought a crapload of 2A "bricks" that provide faster charging. I was carrying around 1A bricks with me and when I was sitting in the doctor's waiting room or the ER with my wife, they would charge slowly. Once I started carrying a 2.1A or higher brick with me the phone would often reach 100 percent by the time we were out of the waiting room. That doesn't mean it charges super fast. It means we did a LOT of waiting. But with 1A chargers the phone would only get about a 20% boost while with 2A chargers it did seem to go twice as fast.

    I also have a Samsung GS4 issued by my job. I haven't noticed a difference in charging it with 2A vs 1A but I will try to pay attention once I start using the phone regularly again. The best way to find out if your phone can take advantage of faster charging is to do a test using a "standard" 1A brick one day and a 2A brick the next and observe the difference in charge rates. You might not get the full 2.1 or 2.4A but you might get 1.5A which is still faster than charging at 1A.

    Cables aren't going to make a huge difference. When you consider the wire gauges involved and the short lengths we are talking only a slight difference in charging time. Of course if you have a 2m or 3m cable then by all means invest in a better cable with larger gauge wire. But for the short little 1m cables, wire gauges aren't going to make that much difference unless you have an extremely cheap cable with wires so thin they are prone to breakage. I would worry more about wire breakage than impact on charge time.
     
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  8. NetBrakr

    NetBrakr Gone With The Wind

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    Thanks r0k for the tip. Honestly I never tried using a 2A or higher charger on my phones; lower amp chargers yes but higher amp charger no.
     
  9. NetBrakr

    NetBrakr Gone With The Wind

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    I tested the chargers. Here is what I did, I let the battery drain exactly 60% and put in the charger and wait for exactly 30 mins.

    1A: 66%
    2A: 67%
     
  10. r0k

    r0k Dazed

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    It might be worth doing a number of trials. Say 5 trials at each amperage. Then you might eliminate "noise" in the data and observe whether there is really any trend for the 2A to charge any faster. Based on your results, I suspect your phone is limiting current to something very close to 1A.
     
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