ELECTRONICS > Samsung Galaxy S2 i9100 inductive charging mod (experiment)
Samsung Galaxy S2 i9100 inductive charging mod (experiment) PDF Print E-mail
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This experiment presentation is meant for educational purposes only.
I am not responsible for direct, indirect, incidental or consequential damages to your phone or yourself.
If you are understand the risks you may proceed reading this article.

Some months ago, after seeing that many new high level smartphones supported officially wireless charging, I decided to have a look if there was some kind of genuine or aftermarket solution for Galaxy S2. A quick search revealed that Samsung had not predicted to have a wireless charge connector on the phone board although it could have quite easily fit one as it did on S3 and S4. So no retail solution was available. Then I had a look at amazon and ebay. Nothing really good and whatever solutions existed were bulky and very expensive.
After having a look at XDA developers I found out that quite a few had tried to fit an HP Palm Pre inductive charging system to their Galaxy S and S2 successfully. After checking at Amazon I found out that the needed parts were at an affordable price to have a go.

Here are the parts I used.
Palm Touchstone Back Cover


HP TouchPad International Travel Kit

HP TouchStone Wireless Charging Dock for Pre 3


Copper Tape


Also you are going to need the genuine extended battery and its battery cover cause we need the extra space of this cover to fit the charging circuit.
Extended Battery


Finally if you need a protection for your phone the bad thing is that there are no protection cases for the extended battery. Also even if you use a gel case the protective cover will prohibit charging of phone. So the only solution is a bumper protector like the one bellow that allows direct access to the back of the phone.
Bumper gel case


Let's get started.
First get the palm back cover and carefully peel off the protective plastic of the inductive circuit starting from one edge.


Be very careful to get it out in one piece. This must be transfered to Samsung's extended battery cover as is else the circuit will not work! Also take care not to harm the sponges at top and bottom of cover. These will be needed to make good electrical contact afterwards.
Notice that the circuit cover (black film) is engraved so that each piece will fit in place to have proper circuit operation.
Take special care not to harm the metal foil on the circuit's cover. This is needed both for magnetic shield and proper transfer of inductive energy to the coil.
Remove the metal disks from the back cover and put them back on the circuit cover at the engraved positions.


Now carefully remove the inductive circuit from the Palm cover very carefully. The copper coil and connections to the pcb are quite sensitive. Try removing without bending.
Also don't use sharp items on copper coil. The coil and the circuit are electrically protected and must stay like that.


Put the circuit face down back to plastic film cover (gold contacts should appear from the window of the black cover film). Use the glue footprint and the engraving to place as accurate as you can.


Ok now that everything is back on the black film, it is time to place the whole assembly on the Galaxy's battery cover. Notice that the samsung's extended battery cover has an opening (see photo) right behind the battery. This is the best place to fit the inductive circuit without having to do extra work. The inductive circuit will fit almost perfectly within that space!
The inducting circuit protection film should still have enough glue to stick on battery's cover without any extra help. Some transparent scotch tape can be used to secure the edges of film after everything is done, if needed.


As a tip, at this point put the Samsung cover on the Palm Touchstone charger to see if the magnet holds it nicely and aligned. Also measure the voltage with a multimeter.
Any voltage above 5Volt to 5.4Volt is acceptable.

I should mention that depending of the Palm Pre cover model you will find the polarity at the output may differ so if you want to try it be extra careful and check it out before making the wirings or you will burn your phone charging circuit!

Now everything is in place. See at the photo bellow the phone and the updated S2 battery cover waiting to be connected.

s2wireless08_1a s2wireless06_1a










Now it is time to start making the circuit connections! Remove carefully your phone's back to reveal the heart of the phone!
The pcb at the left that has the usb connector is the charging circuit of S2. There at the resistor I point at the photo +5 Volts from USB come and positive lead from inductive charging circuit should be connected. Since the whole phone circuit is ground shielded I will use the SIM holder for ground (negative pole).
This means only one wire is needed to be soldered inside the phone and that is probably the hardest part of this mod.


Here is a close up of the point where +5Volts (positive) from the inductive charging circuit can be connected.


A very thin wire could be soldered to the resistor but since this is a charging point, meaning that some current up to half ampere may pass from there, I decided to avoid it. Also the wire must be so flat to allow to reassemble the phone again. I decided to use the copper tape. So I cut a piece of copper tape wrap a part of it in half and in there close to the edge solder a thin naked multi core wire as in photo.


The reason to wrap the copper tape in half is that is must pass in between two components as you can see at the photo bellow without short circuiting them.


Ok time to align and solder the wire.
Alignment must be done very carefully. Also the passing of the copper tape from the phone's shell edge as flat as possible. Still slight lift of the speaker spring connectors with a toothpick may be needed, to make sure that the speaker will continue to operate after closing the shell cause of the increased distance that copper tape's thickness will add. A low power solder gun must be used so as not to harm the precious board. I used a battery operated one which power was just enough to solder the wire on the resistor and keep the risk of melting anything else to the minimum.


Ok here is an extra hint. Think of making some insulation between the copper tape the pcb and the near parts. I didn't because I believe that copper tape is fastened in position securely enough to touch any nearby parts and the pcb's solder resist finishing is applied correctly but maybe increasing the safety could be considered.
Close the shell!


Start making the conductive paths that will bring in contact the back cover with the phone using the copper tape. I found with trial and error that the best position to connect the positive is at the right of the phone (back view) where Samsung for whatever reason was more generous with space.


Make the conductive paths with the copper tape both at the phone and the battery cover. My solution was like the photo bellow. I tried to keep the paths as short as possible. By trial and error again, I found that in some cases the connection between the copper tape parts wasn't good enough (voltage fluctuations) so I used again my low wattage soldering iron to solder these points with very swift movements so as not to melt the cover or the inductive circuit.


Put the battery in.  At the connection point of battery cover with the main phone body, under the copper tape I used foam pieces from the Pre cover to increase the pressure at the conductive points. Notice also that in order to make the circuit slimmer I cut the lower part of the inductive circuit film protector and used it afterwards as the cover above the copper tape at lower battery cover part. Now it looks as elegant as possible for an experiment.
Here is how my phone looks finished.


And here is my phone 3 months after this modification. Next to the Palm Inductive charger.


Inductive charging peacefully!


Observations - Conclusions
1. Inductive Charging takes somehow longer than normal charging.
2. Phone gets a bit warmer during charging than usual.
3. Charging stops when battery full as normal.
4. Touch screen becomes a bit unresponsive and touching point position dances up and down at the charging frequency rhythm when on dock especially directly above the coil position. I believe this is normal since this inductive circuit is not specially designed for S2 and S2 is not designed to be shielded for inductive charging. Otherwise the phone works fine on charger.
5. Have not tried to put on charging dock while phone is connected to usb either for pc connection or charging. I consider it dangerous for phone or computer and will continue to avoid it although in theory there should be no problem. But anyhow if you have your phone connecting with cable it is charging anyway.
6. When using the extended battery the phone will have a very small hump directly behind the battery. If you want it to be perfectly flat you can use the stock battery which leaves about 1,5mm space to the inductive circuit but has less juice.
7. After 3 months of using the wireless charging I have no problem with my phone. The usual habit is that I have it on dock when working at office and charge it by cable at nights next to my bed.
8. Was it worth it? Well I am saving the USB port a few daily inserts so that it will survive for more serious staff like ROM upgrades. Also its easier to use at office since no cables attached. But as far as charging is concerned traditional wired charging seems to be more efficient.

Hope you did find my experiment useful.

Update (03-10-2013): Hi all, it's been six months I have this mod working on my phone. No problems have occured.


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