Samsung Galaxy S7 power without battery

Thread Starter

AYBFunkyMonkey

Joined Jun 20, 2018
6
I am attempting to construct a power supply that will allow me to power my old Galaxy S7 without a battery. I created a thread on the XDA forums since it was cellphone related, but now I realize that my question has become too specific to electronics for that forum, which is mostly focused on software. If you would like to know more reasoning/background on my project, please refer to that thread, I will try to keep my copy/pastes as concise as I can.

Here are the pictures from the disassembled phone:


I purchased a variable voltage adapter from Amazon to try to use for powering directly to the battery terminals inside the phone. I can move the slider to change voltage quite precisely according to my multimeter (unfortunately there isn't any display to see on the power supply itself), and since the battery is labled 3.85-4.4V, I've got it tuned to about 4.35V currently. The amperage reading at this setting shows 3.45A. So I can tell the lower voltage the slider is set to, the higher the amperage reading is. This should be plenty of power, and get around the issue most of the articles I found had where they tried to re-purpose USB connectors, which only put off about 500mA.

The first problem I ran into, is the connector on the S7's board for the battery is tiny! I labeled the pins with my terrible paint skills for a multimeter resistance test:

I have a soldering iron, but its a relatively large old thing and I wouldn't trust it for any thing more precise than 2mm. I've only used it in the past for large speaker wiring and such. I'm thinking about ripping the wiring assembly off of the top of this old battery, and seeing if something in it is more accessible to my soldering. But I'm hesitant for two reasons. First, its quite bloated, and I worry about it exploding if I rip off the wrong part... Second, the battery still works for the most part, and its the only way I have of powering up the phone currently to make sure the phone still works.

Here are my resistance readings on the pinouts so far in Ohms:
A to E = 1 (Must be same pin, will refer as AE from here)
D to H = 1 (Must be same pin, will refer as DH from here)
AE to B = Nothing
AE to C = 595
AE to DH = 630
AE to F = 260
AE to G = Nothing
DH to B = Nothing
DH to C = 880
DH to F = 1012
DH to G = Nothing
B C F G = Nothing in any combination

I came across this site in my searches that may answer some questions if it is accurate. But its written in very bad English so I cant understand most of it. Here is the diagram from the site:

The diagram seems to indicate my AE pins are ground, DH are +, C is the battery sensor, and F is something else. They mention BSI is very important, not sure what that is.

So my first few questions are:
1. Does this circuit board diagram appear accurate? Anyone know what I'm dealing with on those red and green highlighted wires?
2. I've read some phones will shut off anyway under these methods unless a resistor is connected to one of the other pins besides + or -, once question 1 is answered, anyone know what resistance is required based on my readings, and what pin to connect?
3. Any advice on how to wire up the connector physically? My first thought just for testing purposes was alligator clips, but I cannot find any small enough for those tiny surfaces, are there any smaller connectors similar to alligator clips that would allow a temporary yet solid connection? Enough that I would be able to turn the phone over and view the screen to make sure it is powering on correctly.

Please let me know if there is any more information I missed that would help determining the solution.
 

Dodgydave

Joined Jun 22, 2012
8,880
You can't power a mobile phone up without the battery, it needs the battery as a current boost to boot up, as the charger can't provide the excess pulse.

The reason the battery has a multiple connector is to monitor the cells for balancing during charging.
 
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Thread Starter

AYBFunkyMonkey

Joined Jun 20, 2018
6
The battery is rated at 3000 mA though, and the AC adapter I linked outputs 3.45A at 4.35V, isn't that enough? I'm not trying to use a cell charger.
 

jaredwolff

Joined Jul 1, 2017
58
AC adapter I linked outputs 3.45A at 4.35V, isn't that enough?
That AC adapter may be sufficient and that supply would *probably* work but you'd have to make sure that you're not browning out your supply even with those specifications. (Simple test is to attempt to boot with operating on that supply watching the supply voltage on a scope for any significant dips)

I know previously there were typically 3 connections from an MLB to the battery. First and second being power and ground. The last being the analog output of an thermistor. With this connector though, it's quite possible that those lines are being used for data communication with a coulomb counter (or something similar like an I2C controlled temperature sensor) on the PCM itself. Without knowing the specifics, probing those lines when the battery is connected may yield you some important information.
 

Thread Starter

AYBFunkyMonkey

Joined Jun 20, 2018
6
Thanks for the tips. Would I wire the multimeter in series from the + side of the AC adapter? Also I still have the issue of needing some type of connector that will allow me to isolate these extremely tiny contacts. The needles from the multimeter are barely fine enough for the job when the phone is sitting flat on a desk, but I need to be able to turn the phone over to see the screen during the test. Anyone know what type of tool I can use to clamp on to these tiny contacts?
 

jaredwolff

Joined Jul 1, 2017
58
I don’t recommend going at this with regular tools. Your best bet is finding the matching connector (Likely JAE or Molex) and breaking it out to headers on a custom PCB. Even with the right tools I’ve destroyed these connectors quite easily. The plastic does not hold up to soldering irons or hot air.
 

Thread Starter

AYBFunkyMonkey

Joined Jun 20, 2018
6
Ok so I got a cheap replacement battery from Amazon just to have as a backup, and cut the connector off of the top of the old battery. Here is what it looks like:


I ran a resistance test with it connected to the phone's board using the flat metal contacts labeled above, and I got 977 ohms. This doesn't match to any of my previous tests, but judging from this circuit that came off of the battery, there are few more components it is running through.

So anyway, I wired it up to my AC adapter power supply with alligator clips on those metal foil pieces, verifying the voltage again ahead of time, and attempted to power on the phone, but nothing happened. The screen did not light up or flash at all. Just to make sure I didn't fry the phone, I connected the new battery, and was able to boot it normally. (Side note: It seems to run fine with all those former components removed, as far as I know they are the speaker, wireless battery charging coil, and cellular antenna).

Any ideas on what I'm doing wrong?
 

jaredwolff

Joined Jul 1, 2017
58
That was a good call to tear down a battery pack and salvage the PCM. I'm sitting here thinking "why didn't I think of that.." :D

What is your AC adapter's voltage? You want to emulate the battery voltage at about 3.7V.
 

Thread Starter

AYBFunkyMonkey

Joined Jun 20, 2018
6
It's variable, and since the battery is labled 3.85-4.4V, I've got it tuned to about 4.35V currently. I figured that would cover any voltage dips from the draw of the boot sequence.
 

cw96822

Joined May 29, 2019
1
Was this solved. I can't tell from the thread. I'm having the same issue with an LG Rebel 4 that I want to power with a source other than the original battery. How did you get your Samsung to finally boot, if you did?
 

Shummy-

Joined May 30, 2019
1
From what i can see the original poster has the polarity backwards. Positive should be the terminal closest to the FPC flex cable.


 

Thread Starter

AYBFunkyMonkey

Joined Jun 20, 2018
6
I never did get it to boot, this was almost a year ago. I probably did try swapping the polarity and all that, but I gave up on it.

To be honest the only reason I wanted it was to play android games at my desk without wasting batteries, because Bluestacks was not performing well enough for the game. But I since got a newer version of Bluestacks and upgraded my computer and don't have the issue anymore.
 

cpirius

Joined Jul 11, 2011
1
Just because this comes up high on google results, here's some info on how to make it work.

This is the pin out for the connector on the battery. Two pins are for positive and two for negative. Two pins are unused and two are probably for a built in thermistor, but it is not required to run the phone.

Battery Connector.png

The easiest way to connect to the phone is to cut the flex PCB off the battery (be careful not to short the battery while you do that) and solder wires to it after scrapping off the masking material.

Phone Battery To Wires.jpg

Then just connect it with 4.2V with a supply that can provide up to 3A and the phone will boot just fine. (Really this should work from 3V to 4.2V input)

The phone will try and "charge" your power supply if you connect the phones USB at the same time, so I would recommend against that, at least for long periods. It's most likely ok with most supplies, but not ideal.
 
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