Help my understand why my cell phone charger current quantification failed!

[BetaTest]

Hi Every! Thanks for reading.

 

I'll start off by saying I'm not sure if this is the right sub forum for this question and I apologize in advance if I have posted in error.

 

I wanted to do a simple experiment to compare the current output of 4 different usb charging bases. I used a multimeter and modified usb wire.

 

If you're not familiar with this item here is a quick intro: To charge many devices at home a "wall charger" is usually included. It consists of a base that plugs into the wall outlet and has a usb port. A usb cable is used to connect the base to the device (phone / tablet / etc...). Most bases are typically 5 Volts and have a current between 1.0 amps to 2.1 amps.

 

What I did: I dissected a spare usb wire to find the "hot" or current carrying wire. I cut that wire and put my multimeter in series with the phone. Then I set up the multimeter and plugged in the base, the phone, turned on the multimeter and observed the current.

 

The Problem: The currents I observed on all four charging bases was well below what was expected. I observed currents in the range of 200-400 mAmps. I was expecting to see between 1.0-2.1 Amps. The test phone I was using showed the charging icon when the multimeter was activated but it was only getting enough current to maintain its current level of charge but not to actually charge up.

 

What I'm trying to understand: Basically I'm trying to understand why I didn't observe the currents I was expecting. The multimeter I was using should measure currents all the way up to 10 Amps! Did I add too much resistance to the circuit? Was the voltage drop changed by the multimeter?

 

Any insight would be much appreciated!

 

-BetaCase

 

 

[Mordred]

cell phone chargers trickle charge, you don't want to charge a cell phone battery too fast as it will reduce its life expectancy.

[pwagen]

Measure resistance between the D+ and D- on the USB connection. If the resistance is >200 Ohm, the device won't recognize it as a dedicated charger, as far as I've been able to tell, so it won't deliver the full current.

 

Pinout:

http://www.thice.nl/wp-content/uploads/2010/06/Milestone-dock-adapter-pinout-microUSB1.png

[BetaTest]

Is there anything I can put in the circuit to make it draw the maximum current from the base?

[pwagen]

Did you measure it? If you're using a normal USB data cable, it's probably lacking the resistor which lets the device recognize it as a dedicated charger port. If so, connect the data pins to each other with a resistor of <200 ohms.

 

Here's a schematic of a normal USB connector, but it should be the same principle with a micro USB one:

http://m.eet.com/media/1169154/usb%20pwr%20conn.jpg

 

Don't mess up though. I once shorted my phone with a home-made charger cable because I'm an idiot.

[BetaTest]

I made this diagram in the hopes of more clearly demonstrating my setup.

 

[Sensei]

Imagine you have discharged cell phone battery to null.

 

How long it takes you to charge it to 100% full again?

 

I was expecting to see between 1.0-2.1 Amps.

 

If your cell phone battery has 1000 mAh, and loading current would be 2.1 A, it would charge to full in just 500 seconds = 8 min 20 sec (let's assume no loses). With 0.2 A, it would be 80 mins+.

 

Mine cell phone battery has 3.7 V and 3.7 Wh on its back. Which is 1000 mAh.

 

Did I add too much resistance to the circuit?

 

How could you do it?

Typical voltage meter has as largest resistance as possible, usually a few mega ohms AFAIK.

And ampere meter has the smallest resistance as possible.

http://www.allaboutcircuits.com/vol_1/chpt_8/5.html

Edited June 3, 2014 by Sensei

[Spyman]

Basically I'm trying to understand why I didn't observe the currents I was expecting.

The phone is intelligently managing and choking the current to prevent the batteries from getting to hot and be damaged.

[Mordred]

here this site will help, as I stated earlier it is trickle charging and also

 

The phone is intelligently managing and choking the current to prevent the batteries from getting to hot and be damaged.

 

 

http://www.electroschematics.com/4983/usb-mobile-charger/

 

you never specified which cell phone you have but different cell phones have different charging requirements here is a brief list

http://sindhu.ece.iisc.ernet.in/systemslab/documents/cellphone_chargers.pdf

[BetaTest]

Hi Everyone! Thanks for the replys.

 

The phone I'm using in my testing is a Samsung Galaxy S3 with a 3.8V 2100mAh battery. Mordred I'll be reading that pdf as soon asI get a chance!

 

Sensei I never did the calculation of the charge time but I agree it makes sense. However consider this evidence:

 

1) The phone charges faster with a 2.1A charger compared to a 1.0A charger

2) When I play certain games, a 1.0A charger will not be able to keep us and the battery slowly discharges. Even some cheaper 2.1A chargers won't keep up.

 

This was the reason I decided to conduct this experiment!

 

I think that there is some loss in my circuit; because of your input I decided to measure the charge time. It was at this point I realized the phone was not charging and was actually very slowly losing charge. So I have to find the point at which this is happening!

 

-Beta

Edited June 3, 2014 by BetaTest

[Sensei]

The phone I'm using in my testing is a Samsung Galaxy S3 with a 3.8V 2100mAh battery.

2.1 A * 3600s = 7560 C.

 

7560 C / 2.1 C/s = 3600 s = 1 hour to charge to full with 2.1 A current. Is it plausible estimated time (assuming you don't play game at the same time ) ?

 

Sensei I never did the calculation of the charge time but I agree it makes sense. However consider this evidence:

Amper hour unit Ah is simply 3600 Coulombs.

1 Coulomb is 6.24*10^18 electrons.

 

1) The phone charges faster with a 2.1A charger compared to a 1.0A charger

That's no surprise. After all it's more electrons per second. 1 A is 6.24*10^18 electrons, 2.1 A is 1.31*10^19 electrons per second.

 

2) When I play certain games, a 1.0A charger will not be able to keep us and the battery slowly discharges. Even some cheaper 2.1A chargers won't keep up.

Apparently these games are using more energy than charger is able to provide. I guess so, heavy 3d.

Do you have app showing cpu/gpu percentage usage with history.. ?

 

I think that there is some loss in my circuit;

Perhaps some application running all the time in background that's eating energy?

 

Also loading a lot data to memory might have such effect. Typical computer random access memory must be refreshed periodically by current to sustain content.

 

I had one Nokia 10 years ago that ate power like crazy when it was full of data. After deleting everything it could work several times longer.

 

Current ebook technology is using screens that use power only while changing display. Games changes display even 30 FPS. Not sure whether such screens are used by some mobile phone. Might be highly model dependent.

Edited June 3, 2014 by Sensei

[BetaTest]

Perhaps some application running all the time in background that's eating energy?

 

Also loading a lot data to memory might have such effect. Typical computer random access memory must be refreshed periodically by current to sustain content.

 

I had one Nokia 10 years ago that ate power like crazy when it was full of data. After deleting everything it could work several times longer.

 

Current ebook technology is using screens that use power only while changing display. Games changes display even 30 FPS. Not sure whether such screens are used by some mobile phone. Might be highly model dependent.

 

First, thanks for the informative reply Sensei.

 

I should have been more clear. The second part of my post about "having loss in my circuit" was not about normal charging that I do. It refers specifically to the experiment with the modified usb wire and the multimeter in series. Simply put, when I use the wire with my setup the phone receives some current but not enough to charge. During all of my testing there are no games or apps running, just the OS.

 

I have one charging base that works really well, and even using that base with this modified wire the phone is still losing charge slowly.

 

-Beta

[pwagen]

Out of interest, how many internal wires does the USB cable have?

[BetaTest]

Four wires (sometimes 5)

 

Vcc +5V (Red)

D+ (White)

D- (Green)

Ground (Black)

 

+Shielding in some wires

Edited June 3, 2014 by BetaTest

[Klaynos]

And do your descriptions hold true for power only devices?

 

I was under the impression that many charges used the data channels for power as well. Assuming the device supports this. Power loss in cables had also been cited as an issue, I've not really investigated this though.

[BetaTest]

Klaynos,

 

I haven't done much research on this topic either, but what I have done led me to believe that there are two types of usb wire:

 

1) Data cable - which is similar to the diagram above with the D+ and D- there.

2) Charging cables - where the D+ and D- are shorted which lets the device know that it can charge at full speed.

 

I'm not sure if my cable is shorted or not.

 

=============================================================================

 

Back on topic.

 

Since the phone can no longer charge effectively with this setup, it has led me to believe that there is some power loss or connection loss between the wire / probe connection. I'm looking to try different methods of connection to endure a consistent connection!

 

-Frozen

[Mordred]

have you tried a fresh battery? part of the circuitry in the cell phone detects the required charging level to full charge. I've seen similar problems being due to the battery itself, some batteries also have circuits in them. Never tore apart the S3 battery though.