How to test the efficiency of the phone

Ideas and questions about MintyBoost kits

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George_42
 
Posts: 3
Joined: Tue May 13, 2014 11:04 pm

How to test the efficiency of the phone

Post by George_42 »

Hello,
I have just built my first minty-boost, including a power button and a JST connector for a lithium ion/polymer battery input. While going through the math, I noticed that it stops at the output of the minty-boost kit. It shows the math for the battery going to the minty-boost, and then the math of what the minty-boost outputs at the USB port. The math math for what the phone battery actually receives is missing, and is something I would like to find.

Steps I have taken so far
I first contacted my phone's manufacturer. I asked them what the charging efficiency of the internal charger of my phone was. They did not know. Their engineers are in Korea, so I was unable to ask them directly.
I then contacted support of other phone manufacturers to attempt to find the charging efficiency of similar devices. Apple seemed hopeful, and gave me an efficiency of 100% of the iphone 4. By this, my phone would also have a 100% charging efficiency.

Further ideas for action
I could try to drain my phone's battery completely, and then charge it completely. If i timed the charging process, I could come close to the efficiency if i knew the voltage and current of the charger. The two problems with this idea is that my phone will be consuming energy in places other than the charger while this goes on (as my phone requires power to check its charge level), and accurately clocking this would be difficult.
I could try to exactly match the mah of my phone battery, and input it into the phone, then check my charge level when the minty-boost dies. This would be easier to clock, and would not require me to check my phone. It would also require me to put multiple lithium ion/polymer batteries in parallel, which checking on the forums suggests to be a bad idea as the batteries will discharge into each other.

My question
Is the charging efficiency of a phone essentially 100% like my experience with Apple would suggest? How would you find this efficiency? Do I need to worry about the loss from the USB charging cable itself, or is it essentially 0 like the wire on a breadboard? How could I calculate the cable's efficiency knowing wire gauge and length?

Numbers in case you need them
minty-boost battery: 6600mah, 3.7V, from the adafruit store
phone battery: 1830mah, 3.8V
USB cable: 22 gauge, 12 inches

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adafruit_support_bill
 
Posts: 88097
Joined: Sat Feb 07, 2009 10:11 am

Re: How to test the efficiency of the phone

Post by adafruit_support_bill »

100% is pure fiction. I have heard that it is possible to get up around 98% with a slow enough charge rate. But if your phone gets even the least bit warm when charging, that heat is energy that is not getting stored in the battery. The typical 'rule of thumb' for back-of-the-envelope calculations is in the 80-85% range.

George_42
 
Posts: 3
Joined: Tue May 13, 2014 11:04 pm

Re: How to test the efficiency of the phone

Post by George_42 »

Thank you. I will simply use 80% in my calculations, and think that it includes the loss from the cable. After reading another post on loss of power over the cable, I think I shall try to find an even shorter cable.
Thank you again.

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