Saturday, June 20, 2015

Using a Samsung 2A travel adapter with adaptive fast charging with MotoG : How does it behave? part 1 : first overview

My old Sony-Ercisson 850mA charger is ageing and i needed a new and more powerful one. i Bought the Samsung 2A travel adapter with adaptive fast charging model EP-TA20EWEUGWW (white one, with French 2 pins male plug)
  • We can read everywhere that a charger will only provide what the device is capable to take, is that right?
  • Is that really safe to charge a MotoG (specified to be capable of charging between 550 and 1500mA by the manufacturer) on a 2A adapter?
In the way chargers work, it should be ok, but does the device really behaves the way it is intended to?


Materials and Methods
Trying to keep things objective
  • To monitor input Current:
    A wattmeter:
    It has a precision of +/- 1W that isn't precise at all, but this is only to roughly monitor the input current. ==> this inaccuracy will prevent me to give good efficiency predictions...

  • To "monitor" output current: Ampere
    the app is not meant to be accurate, the idea is only to have an approximation of the current delivered by the charger.
    • The device uses between 180 and 300 mA when idle, screen ON, wifi ON.
    • Ampere mesurements display current applied to the battery, not the one coming from the adapter; so we will add 250mA to the results (or 160 with the experiments without wifi).
    • Therefore if Ampere displays +1000 mA that would mean that the adapter provides about 1250mA and Battery gets 1000mA.
    • Considering previous experiments we can assume that the results are accurate at +/-100mA; this means that when Ampere displays 1000mA, the charger provides something between 1150 and 1350mA (displayed current +250 +/-100)
  • To monitor Temperature:
    Temperature is monitored with the pm8226_tz probe that looks like to be linked with the power manager of the battery -aka battery 'charger' when device is plugged to power source-
Chargers characteristics:
Sony: 5V 850mA
Samsung: 5V 2A or 9V 1.67A with fastcharging capable devicer (EP-TA20EWEUGWW)
For this first experiment the device was discharged down to about 50%




Efficiencies
When results are so inconsistent that you cannot really conclude -_-'
Sony at 50% charge:
  • Input power: 6W +/-1
  • Output power: 3.75~4.75W (5V 750~850mA)
  • Efficiency : 54~95% (worst_case~best_case)
Samsung at 50% charge:
  • Input power: 8W +/-1
  • Output power: 6.35~7.35W(5V 1270~1470mA)
  • Efficiency: 70~105% (No, current is not coming from anywhere, this 105% is due to the +/-1W inaccuracy of the input wattmeter!)

As best case condition cannot be used, let's see for worst cases:
Samsung worst case is above the sony's worst case so we can at least say that this adapter is NOT LESS efficient in this specific condition [50% battery, room temp @21°C ...]. As i don't have enough data yet -and the worst monitoring tools available- i am not able to say that the Samsung Charger is more efficient.



Overheating
When spare Watts become heat?

Sony at 50% charge :
Battery charging current was about 600mA meaning that the charger was providing 850+/-100mA, considering the charger cannot provide more than 850mA, the real value is somewhere between 750 and 850mA.
pm8226_tz T° is about 43°C, this threshold is never exceeded.

Samsung:
  • at 50% charge :
    Battery charging current was about 1120mA meaning that the charger was providing 1370mA+/-100 pm8226_tz rises up to 51°C until the 70-75% of charge are reached,
  • Then (70%+) current is limited to about 800mA and T° decrease slowly to reach 41°C at 80%.
  • At 89% current is only 400mA pm8226_tz only 37°C and the Input current is lowered at 3.2W.
  • When fully charged, idle and screen ON, the adapter still uses 1.9W from home circuit. which means that with an efficiency of about 70% the adapter provides about 226mA which corresponds to the device usage. When screen is OFF, the adapter input current drops under the watmetter detection threshold.

Here is a chart showing Charge Current and pm8226 Temperature against charging percentage.

Now, the questions are,
  • what happens before 50% ?
  • Does the adapter reaches the 1500mA that the device is theorically capable to handle?
  • Is the device really able to handle that much Current ?
  • How does the temperature increase if the device is NOT totally idle while charging?
  • Will the battery survive multiple full charge this way?
Some answers in a few days, after i tried and get more data -and hopefully not fried my device xD-.

Quick Update before the full article : my MotoG power management unit (pm8226) reaches up to 57°C when using it really little while charging, i don't think it is safe at this level of heat ...

If i had better tools, i would try to make accurate charts about :

  • pm8226 and battery T° (C) and Current (mA) against battery charge (%)
  • Battery charge (%) agaisnt time (min)
  • Charger efficiency (%) against Battery charge (%)
  • Monitoring surface T° with a IR camera
  • ...