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Findings on Galaxy S4 charging current

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spark001uk

Senior Member
Jan 14, 2010
705
154
Surrey, Untidy Kingdom
With the advent of the S4, and its higher capacity battery, one could understand a higher charging current. However, I seem to have uncovered some findings that the charging system on the S4 is a bit more complex than first thought!
This is a bit techy, and assumes you have a basic amount of electrical knowledge, ie voltages, currents, resistance etc., but I'll try and keep it as simple as possible for anyone who may not!

To explain: The mains charger supplied with the S4 is a model number ETA-U90UWE, rated 5V @ 2A. However, the phone will ONLY charge at full current (which as I have measured so far, depending on what the phone regulates it to, typically sits in the region of 1.2 - 1.5A), when using the supplied charger (or possibly one of equal or higher current rating, depending on how it's configured internally), AND the supplied usb cable, OR any other usb cable, provided its shielding (the metal outer surface of the connectors) is connected at BOTH ends of the cable. Use a cable that doesn't have this shielding, and the charge current drops, regardless of whether there is plenty of current available or not. Use a different charger with an unshielded cable and the current drops even more, again regardless of whether it can supply plenty more current.
My assumption on this, is possibly an effort by Samsung to avoid the scenario of sticking 1.5 amps down a flimsy cheapo cable, the wires of which will likely be too thin to carry it.

After doing some probing around with a meter, I have managed to find a slight difference with the charger itself, compared to a generic one. In a generic one, the two data pins are usually just shorted together, which tells most phones that it's a mains charger rather than a USB port. On the Samsung one on the other hand, the pins appear to be shorted together, and also connected via resistors across the supply line (known as a potential divider), which holds these shorted data pins at a certain voltage. This is what tells the phone what sort of charger it's connected to.

Attached are a couple of diagrams to show the difference between the two chargers. There are in fact various setups of resistors that different manufacturers use to set the charging current, so it's quite easy to run into compatibility issues!

To make this a little less confusing I have done some preliminary experimenting, and I set out my results here.

For the test, I used combinations of 4 different usb style mains chargers: an apple iPhone one rated at 1A, an iPad one rated 2.4A, an HTC 1A one, and the genuine S4 one. With these I used two cables - the supplied Samsung S4 one (which is shielded), and a cheap generic one (which isn't). I started by measured the charging current directly with a meter, by using a very short usb breakout lead I've made, enabling me to interrupt the 5V line. However, I soon noticed that the use of any extension cables, even shielded, can lessen the chance of maintaining a good shielding connection, so I continued the exercise relying on the "galaxy charging current" app to get a reading.

Charger.................... Cable................ Current (A)
=====================================
HTC 1A.................Generic..................... 0.5
HTC 1A.................Samsung S4..............1.0

Apple 1A...............Generic......................0.5
Apple 1A...............Samsung S4..............1.0

Apple 2.4A............Generic......................0.6
Apple 2.4A............Samsung S4..............1.3

Samsung S4.........Generic...................... 0.8
Samsung S4.........Samsung S4...............1.3

So as you can see from these results, the original charger makes a difference, and the supplied cable (or a good quality shielded one) makes a further difference. If you have any further findings please feel free to add them here.

I can see that this is going to confuse some people, as it has me, as I'm sure some will inevitably try charging up their phone on generic chargers/leads at some point, with potentially long charging times resulting!

.
 

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pintycar

Senior Member
Apr 5, 2011
63
16
Very nice findings! Thanks for sharing them.
Not only what you say about longer charging time, but also discharging may occur (it has with me) while connected to the USB. I left my phone with USB tethering and it shut itself down after a couple of hours (it was low on battery already). I wanted to keep all the accessories in "new condition" in case I sell the phone in a few months, but I guess this justifies using the official charger and usb lead.
I hope someone can shed some light on the detection mechanism or the particular characteristics of the official cable so it can be replicated in generic ones.
 
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follo

Senior Member
Jun 19, 2008
58
7
Reggio Emilia, Italy
You could try to add an extension cable to check if the charging system needs exclusively an original samsung cable from the charger to the phone.

Original samsung charger => extension cable male/female => original samsung cable => phone

PS: is there an app to check the charging current?
 

spark001uk

Senior Member
Jan 14, 2010
705
154
Surrey, Untidy Kingdom
My experiments used an extension cable, that's the one I made into a breakout cable. So no it doesn't change by adding a cable.

There is an app, called galaxy charging current, which I tried also. In the 0.75A results above it showed a max permissible current of 1000mA, with the fully samsung setup it showed 1900mA. In the lower scenarios is showed up as 460mA. Other than that it doesn't tell you anything, it literally just shows you a max possible current, not the actual current it's drawing.
 

spark001uk

Senior Member
Jan 14, 2010
705
154
Surrey, Untidy Kingdom
I've found out what the issue was, my generic cable was obviously a cheap one and wasn't shielded! I have edited my original post to re-explain.

Also I did a further test on a PC usb port - the Samsung cable allowed for 500mA, but the unshielded cheap one only allowed about 350mA, so (as pintycar found out), the phone actually carries on discharging in this case!
 

demusss

Senior Member
Mar 2, 2008
68
9
Interesting post.

I've been trying to mod a car charger so that the s4 draws more than 300mA so far unsucessful. I'm going to add in the 82K resistance and see what happens.
 

wmccann2

Member
Jun 12, 2008
19
14
Interesting post.

I've been trying to mod a car charger so that the s4 draws more than 300mA so far unsucessful. I'm going to add in the 82K resistance and see what happens.

Hi,

Using a 5a digital bench power supply, I took a normal micro USB cable, cut it in two, added in the 82k resistors and tested.

Before: 450ma, after 1.73a

Then using a clamp meter I tested it with a 2amp Asus tablet charger - it varied between 1.48 and 1.61 amp.

I have since built a few more cables - one to use in my car (again 2 amp charger).

All in all, it works very effectively. Thanks for the initial research (saved me having to open my charger.)

BTW I suspect it is the charger where the resistors are, not the cable, otherwise the phone would try to pull 1.5a + from a laptop if you connected it.

Left my samsung cable at work so will test it tomorrow (if I remember)!

W.
 

Paparasee

Senior Member
Apr 19, 2009
1,105
198
Kuwait
Interesting. So basically for us laymen, you are telling us to use the original charger and cables to the extent possible ... right?

Can you clarify to me what an unshielded cable is? Maybe with a picture? I've got a blackberry's cable at work connected to my PC.

At home, I also have a cable and charger that I got with my Nexus S (I think this says Output 5.0V ~ 0.7A).

Would this be a problem or can I get by with these?

Thanks :)
 
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Xphome

Member
May 1, 2013
27
1
Vänersborg
I've been using the Samsung cable+charger+USB extension cable and charging the S4 usually takes about 4 hours, I'm going to try with just the Samsung cable next time and see if it makes any difference since people are saying that theirs can be fully charged within less than 3 hours.
 

wmccann2

Member
Jun 12, 2008
19
14
Interesting. So basically for us laymen, you are telling us to use the original charger and cables to the extent possible ... right?

Can you clarify to me what an unshielded cable is? Maybe with a picture? I've got a blackberry's cable at work connected to my PC.

At home, I also have a cable and charger that I got with my Nexus S (I think this says Output 5.0V ~ 0.7A).

Would this be a problem or can I get by with these?

Thanks :)

Hi,

I believe (guess work here ) that only the original charger "needs" a shielded cable - could be checked by shorting the ground and shield on one side and see if it works at the higher current - if I am bored I may do it - it probably checks the shield and limits the current if it is not there (note I have not tested this so only going by the first posters findings).

BTW a shielded cable has a wire mesh around the 4 internal cables - this mesh avoids external interference messing with the signals. Can't see it affecting the charging though BUT shielded cables tend to have thicker internal cables so could be related to this.

I have it charging at 1.7a on an unshielded cable (thought he power strands are thicker than average) Shielding should only affect the data transfer speed, not the charging current.

If the Nexus S has only a 700mah charger then this will not be able to provide enough current for high speed charging and could easily burn out - nice smell, dead charger, not much else. therefore only use a normal unmodified usb cable (and it will charge at about 450mah).

W.
 

Drukkie

Member
Dec 8, 2010
41
5
For what it's worth I'm charging with a Note 1 charger...a thick shielded cable via the S3 docking station....and getting 900mah...
will get my original cable tonight and have a go tomorrow...
 

DaveG46

Senior Member
May 4, 2012
52
4
interesting read, my s4 lead and charger are still in the box and I'm using my nexus 10 ones phone charged from about 30% to full in just over 2. may have to change the old HTC £2 lead I've got connected to my works pc then, maybe why it's struggling to charge when playing music. guess this is one way to get people to buy more expensive cables
 

heliocrux

Member
Jan 4, 2013
14
2
Cebu
Very interesting read, thanks TS.


My original charger and cable set is still in the box; I've been using my Mom's old Galaxy Note charger.


I'll try the original cable + wall mount and see how fast it is compared to my current charger.
 

coolraghav

Senior Member
Dec 8, 2008
143
15
After this thread I have stopped using my blackberry bold cable to charge s4 and of course the cheap one too.. thanks op!

Sent from my GT-I9500 using xda app-developers app
 

Entropy512

Senior Recognized Developer
Aug 31, 2007
14,095
25,088
Owego, NY
I'm not sure if shielded vs. unshielded is the difference - probably wire gauge is the difference.

For example, if you shop at Monoprice, you have two options for USB cables: 28 gauge cables, and 24/28 gauge cables.

For wire gauge, lower is larger - the 24/28 gauge cables have thicker wires for the + and GND lines. A pure 28 gauge cable is likely to drop voltage a bit at high currents, and my observations have been that most newer devices, ESPECIALLY Qualcomm-based ones, are VERY finicky when it comes to input voltage drops.

As to the charger itself:
Apple chargers are almost guaranteed not to charge at full current, as they don't conform at all to the USB battery charging standard. Some newer Android devices do have at least partial detection of Apple chargers, so they may charge at 1A if an Apple charger is detected (any Apple charge, even 2.1A ones).
It sounds like the included official charger is a tablet-compatible one. Samsung tablets expect D+ and D- to be held by the charger at 1.2 or 1.8 volts (I forget which). As a result, Samsung tablets will not charge from standard chargers (like an N7 charger), but standard devices (like an N7) will charge from Samsung tablet chargers.

Now, the question is: Does the GS4 *require* a Samsung tablet-style charger, or did Samsung just include a tablet-style charger because it's backwards-compatible with standard devices? (less part numbers to track in inventory).

A useful pair of points would be: Using the same cable, does the Samsung charger behave significantly different from a Nexus 7 charger?
 

Entropy512

Senior Recognized Developer
Aug 31, 2007
14,095
25,088
Owego, NY
Hi,

Using a 5a digital bench power supply, I took a normal micro USB cable, cut it in two, added in the 82k resistors and tested.

Before: 450ma, after 1.73a

Then using a clamp meter I tested it with a 2amp Asus tablet charger - it varied between 1.48 and 1.61 amp.

I have since built a few more cables - one to use in my car (again 2 amp charger).

All in all, it works very effectively. Thanks for the initial research (saved me having to open my charger.)

BTW I suspect it is the charger where the resistors are, not the cable, otherwise the phone would try to pull 1.5a + from a laptop if you connected it.

Left my samsung cable at work so will test it tomorrow (if I remember)!

W.

I missed this post on my first read-through: What happens if you just short D+ and D- when using the bench supply?
 

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  • 99
    With the advent of the S4, and its higher capacity battery, one could understand a higher charging current. However, I seem to have uncovered some findings that the charging system on the S4 is a bit more complex than first thought!
    This is a bit techy, and assumes you have a basic amount of electrical knowledge, ie voltages, currents, resistance etc., but I'll try and keep it as simple as possible for anyone who may not!

    To explain: The mains charger supplied with the S4 is a model number ETA-U90UWE, rated 5V @ 2A. However, the phone will ONLY charge at full current (which as I have measured so far, depending on what the phone regulates it to, typically sits in the region of 1.2 - 1.5A), when using the supplied charger (or possibly one of equal or higher current rating, depending on how it's configured internally), AND the supplied usb cable, OR any other usb cable, provided its shielding (the metal outer surface of the connectors) is connected at BOTH ends of the cable. Use a cable that doesn't have this shielding, and the charge current drops, regardless of whether there is plenty of current available or not. Use a different charger with an unshielded cable and the current drops even more, again regardless of whether it can supply plenty more current.
    My assumption on this, is possibly an effort by Samsung to avoid the scenario of sticking 1.5 amps down a flimsy cheapo cable, the wires of which will likely be too thin to carry it.

    After doing some probing around with a meter, I have managed to find a slight difference with the charger itself, compared to a generic one. In a generic one, the two data pins are usually just shorted together, which tells most phones that it's a mains charger rather than a USB port. On the Samsung one on the other hand, the pins appear to be shorted together, and also connected via resistors across the supply line (known as a potential divider), which holds these shorted data pins at a certain voltage. This is what tells the phone what sort of charger it's connected to.

    Attached are a couple of diagrams to show the difference between the two chargers. There are in fact various setups of resistors that different manufacturers use to set the charging current, so it's quite easy to run into compatibility issues!

    To make this a little less confusing I have done some preliminary experimenting, and I set out my results here.

    For the test, I used combinations of 4 different usb style mains chargers: an apple iPhone one rated at 1A, an iPad one rated 2.4A, an HTC 1A one, and the genuine S4 one. With these I used two cables - the supplied Samsung S4 one (which is shielded), and a cheap generic one (which isn't). I started by measured the charging current directly with a meter, by using a very short usb breakout lead I've made, enabling me to interrupt the 5V line. However, I soon noticed that the use of any extension cables, even shielded, can lessen the chance of maintaining a good shielding connection, so I continued the exercise relying on the "galaxy charging current" app to get a reading.

    Charger.................... Cable................ Current (A)
    =====================================
    HTC 1A.................Generic..................... 0.5
    HTC 1A.................Samsung S4..............1.0

    Apple 1A...............Generic......................0.5
    Apple 1A...............Samsung S4..............1.0

    Apple 2.4A............Generic......................0.6
    Apple 2.4A............Samsung S4..............1.3

    Samsung S4.........Generic...................... 0.8
    Samsung S4.........Samsung S4...............1.3

    So as you can see from these results, the original charger makes a difference, and the supplied cable (or a good quality shielded one) makes a further difference. If you have any further findings please feel free to add them here.

    I can see that this is going to confuse some people, as it has me, as I'm sure some will inevitably try charging up their phone on generic chargers/leads at some point, with potentially long charging times resulting!

    .
    3
    my findings are :

    galaxy s4 (i9505) , charging current reported by Charging Widget

    the original charger has 5.08V , and 1.2V on Data lines.

    but the S4 will not specially need 1.2V on D-lines, just them joined (D- connected to D+). because i have made several tests with or without 1.2V on these lines, makes no difference, it will still draw maximum (1900mA).

    the phone during charger connection will raise the current until the voltage drops to an acceptable minimum of ~4.85V and stay at that current. if the voltage drops a little and then raises, the current will raise too.

    for example: i connected to a lab power supply (variable voltage) a female USB A connector (with D+ and D- joined) .
    -test 1: i set the voltage to 5.1V on the supply . using the original S4 usb cable i was getting 1320mA reported current. i raised the
    supply voltage to 5.5V and bingo, 1900mA current.
    -test 2: same situation, generic microusb cable : i have to raise the voltage on the supply to 6V to get 1900mA... (so much voltage drop on USB Female connector...)

    strange , when S4 reports 1900mA charge, on the lab supply it shows only 1720mA load... and when the screen turns off it shows 1540mA load... so i guess it's not so real the 1.9A load shown on the phone...

    after, i connected the same generic microusb cable to S4 original charger, guess what... 1900mA .... (and this cable doesn't even have Shield connected)

    Conclusion: original cable is so good, because it has Shield wire connected (so it doubles as a GND wire, helping to reduce GND track resistance) and because it has good quality USB A connector (same is the S4 charger USB connector) . It's important that the pins inside the USB connector make good contact (low resistance).

    so if you want to use a generic 2A car charger or home charger, it's important that the charger has good quality USB connector . a sollution if you use a generic China 2-port 2.1A ipad charger (around 2-3$) to make an usb cable that connects to both ports (i was able to get only 1.2A connected with single port with original S4 usb cable) to get the maximum current . Don't forget first to connect D- to D+ inside the charger.

    Or if you use good quality charger and get maximum current with original cable but not with other cables, that because some low quality cables have thin wires inside, low quality connectors , and don't have Shield connected (which would've improved GND wire thickness , lowered it's resistance). I have several 1$ usb-microusb cables around, using them with original charger i got currents like 300mA-700mA, so crap....
    3
    Hi Rob,
    Can I ask about S4 charger ? To get 1900mA, we can just use the original cable or we need to short the D-&D+ pins first ? Thanks.


    Hello,

    For 1900mA you need two things:

    A) Have a sufficient charger (2+Ampere) and let the phone know, that it is connected to a high current charging source. I think it is done via connecting D+ and D- on the galaxy models, but I am not 100% sure here.

    and even more important:
    B) Deliver enough voltage to the Galaxy mainboard. This can be a problem, cause with a high current like 1900mA and the small diameter cables and small connectors you loose some voltage in the cable on the connectors.

    So if the charger sends 5V to the line, on the mainboard you get LESS than 5V on 1900mA. So the Phone maybe does not charge with 1900mA, cause the voltage on the mainboard is to low.

    Cause of that the S4 charger is intelligent. If a phone draws 1900mA from the charger, the charger raises its output voltage from 5,0V up to 5,3V to compensate the voltage loss in the cable.

    So if you have a non-intelligent 5V charger that can deliver (for example) 5A but always stays at 5,0V it can be, that the S4 still can not charge with 1900mA.

    You need a good cable, correct charger identification and a good / matching charger.

    BR
    Rob
    3
    Interesting. So basically for us laymen, you are telling us to use the original charger and cables to the extent possible ... right?

    Can you clarify to me what an unshielded cable is? Maybe with a picture? I've got a blackberry's cable at work connected to my PC.

    At home, I also have a cable and charger that I got with my Nexus S (I think this says Output 5.0V ~ 0.7A).

    Would this be a problem or can I get by with these?

    Thanks :)

    Hi,

    I believe (guess work here ) that only the original charger "needs" a shielded cable - could be checked by shorting the ground and shield on one side and see if it works at the higher current - if I am bored I may do it - it probably checks the shield and limits the current if it is not there (note I have not tested this so only going by the first posters findings).

    BTW a shielded cable has a wire mesh around the 4 internal cables - this mesh avoids external interference messing with the signals. Can't see it affecting the charging though BUT shielded cables tend to have thicker internal cables so could be related to this.

    I have it charging at 1.7a on an unshielded cable (thought he power strands are thicker than average) Shielding should only affect the data transfer speed, not the charging current.

    If the Nexus S has only a 700mah charger then this will not be able to provide enough current for high speed charging and could easily burn out - nice smell, dead charger, not much else. therefore only use a normal unmodified usb cable (and it will charge at about 450mah).

    W.
    2
    Just got my S4, and I've used the Galaxy Charging Current app to find out how much some of my chargers at home can charge the S4, and I see that with the stock charger and stock USB cable that came with the phone, even though it says it can charge up to 2.0A, I only see 1200mA with the Galaxy Charging Current app, yet it fluctuates between 1900 and 1200, depending if I turn the screen on, is that what it's supposed to do?

    I've also tested a blackberry playbook charger, which is 2A and it also does the same thing as the stock charger+USB, fluctuates between 1200mA and 1900mA. Is it supposed to fluctuate between the 2? I'm assuming it is for when the screen is on or off.

    Just looking for inputs!
    Alright, following my post, here are my findings with Galaxy Charging Current, I have a couple different cables and chargers, coming from a blackberry about 2years ago, I still have this stuff, charging info tested with Galaxy Charging Current:

    Blackberry Chargers
    Blackberry Playbook Charger – 5V & 2A – Charging S4 @ 1900mA
    Blackberry Cell Charger – 5V & 700mA – Charging S4 @ 860mA

    ________ Charger ________________ Cable________________ Current
    Samsung S4 OEM 5V & 2A – Samsung S4 OEM USB – Charging S4 @ 1900mA
    Samsung S4 OEM 5V & 2A – Samsung S3 OEM USB – Charging S4 @ 500mA
    Samsung S4 OEM 5V & 2A – Blackberry Thick USB – Charging S4 @ 1900mA
    Samsung S4 OEM 5V & 2A – Blackberry Thin USB – Charging S4 @ 1640mA

    Samsung S3 OEM 5V & 1A – Samsung S4 OEM USB – Charging S4 @ 1220mA
    Samsung S3 OEM 5V & 1A – Samsung S3 OEM USB – Charging S4 @ 340mA
    Samsung S3 OEM 5V & 1A – Blackberry Thick USB – Charging S4 @ 1220mA
    Samsung S3 OEM 5V & 1A – Blackberry Thin USB – Charging S4 @ 1180mA

    Computer USB – Samsung S4 OEM USB – Charging S4 @ 460mA
    Computer USB – Samsung S3 OEM USB – Charging S4 @ 460mA
    Computer USB – Blackberry Thick USB – Charging S4 @ 460mA
    Computer USB – Blackberry Thin USB – Charging S4 @ 460mA

    So all in all, it seems like the S3 OEM USB is the worst one of them all, and that blackberry stuff is pretty compatible with the Galaxy S4!