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[Q] Battery % WITHOUT an APP - is it possible?

OP TheJeffster

15th January 2014, 07:38 AM   |  #1  
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Dear team XDA,

I have just got a curly question from a client, and looking to the brain trust for an answer.

Can you tell the % of a battery just through how much current resistance/flow it's drawing from a charger?

Use case: I plug my phone into a charger that is designed to measure how much current the battery is drawing and how much resistance there is to pushing more juice in. Can I theoretically know how full the battery is by external measures without installing and app or knowing the mAh size of the battery.

My initial thought was yes, much like how a trickle charger knows when the battery is full. But the client challenged me and asked what if the phone hardware isn't giving you direct access to the battery, or genuine feedback from the battery.

Any help is appreciated, the more I thin about it the less certain I get.

p.s. This isn't my first post, but it is a new account so just seems that way
15th January 2014, 03:55 PM   |  #2  
Renate NST's Avatar
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No, you can't get a good indication of anything over the USB power line.
A normal battery charger can see the battery voltage.
USB is operating on 5V to charge a battery from 3.7V to 4.2V.
You'll never notice the voltage change externally.
Moreover, your device is using current to do background things anyway.
You won't be able to accurately compensate for this.

What's the matter with an app anyway?
15th January 2014, 10:00 PM   |  #3  
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The issue is it would be a physical device at a venue and has to handset agnostic with no download required. Downloading an app just makes the user journey to long and clunky, needs to be dead simple.

What if the usb charger was specifically designed for this purpose?

Sent from my HTC_0P3P5 using Tapatalk

---------- Post added at 07:00 AM ---------- Previous post was at 06:55 AM ----------

Ow, and thanks for the reply 😊

Sent from my HTC_0P3P5 using Tapatalk
16th January 2014, 07:10 AM   |  #4  
Renate NST's Avatar
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So you want to make a public charging station that knows when somebody is done charging?
That's somewhat easier.
20th January 2014, 12:12 PM   |  #5  
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Quote:
Originally Posted by Renate NST

So you want to make a public charging station that knows when somebody is done charging?
That's somewhat easier.

Hi sorry for the late reply, for some reason I am not getting notifications.

Yes I want to make a public charging station, but I was really hoping to have % of charge. Letting them know when it's finished should be pretty straight forward.

If there is any conceivable way to do % without an App would be great, we are happy to develop bespoke hardware to facilitate.

We have been using an ADAM data acquisition module to monitor AC current into the charger and it's pretty flatline, so not looking good so far:
21st January 2014, 03:09 AM   |  #6  
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The current should drop when the charging finishes.
Ok, all the background apps will confuse matters since they draw current too.

I'd start out by measuring the DC output of the supply, not the AC input.

Here is a project that is semi-related.
It has to do with powering a device without a battery.
Still, it shows the current measuring method.
Measuring battery current accurately

No, you won't be able to tell percentage.
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