Charging Via Rear 4-pin Connector

Hey all,

I've been experimenting with the rear 4-pin connector on the back of the droid 4 (pogo-pins for the inductive charging rear door)

Connected a current limited power supply to Gnd and Vin on the back of my Droid 4 (pin lower right = gnd, pin lower left = Vin) at 5.0V and I had charging occurring at a nice speedy rate. Screen showed charging, amperage was around 1500mA to start scaling down to 1300mA-1100mA as it reached full charge. It seems to pass through the Lithium Ion battery management circuity so appears to be a safe way to dump in lots of power. Obviously these pins are designed to pick up power from the rear inductive charging cover that Motorola produced, but I wanted to try just pure 5.0V power. It appears that it is not bypassing or defeating the battery temp/overcharging safety circuit but of course test at your own will in a safe environment. I personally noted that if the battery was 'warm' the charge rate was reduced to avoid overtemp. Also it would scale down as the on-screen-indicator showed it was reaching full charge.

I’m thinking of grabbing some extra rear covers and making up some drop-in charging stations or alternative inputs (like solar/etc.)

Nice to get away from having to charge on the USB Micro connector which appears to limit charging current and cause wear-and-tear.

This seems like a VERY good thing if someone was building an external battery pack that fit onto the phone (like the one for the iPhone)…you could power it on, charge via this connector, and shut it down whenever you liked. The power draw on the phone drops off massively once it is charged so if you started with a full charge, it could float the battery all the way to empty.

Time to experiment! My first build will likely be a drop-in docking station.

Again, for reference:

Bottom right (when viewing back, camera at the top):
Gnd is Lower Right – Nearest the microUSB connector
Vin is Lower Left – Opposite side from Gnd on the bottom row

Don’t hit it with too much voltage! I limited myself to about 4.8V and 1700mA max. I'd expect over-voltage on these pins could damage the battery management circuity and fry the phone. I was using a good regulated supply with meters.

Cheers,

Just wanted to pop in and say that these pins and this thread were a savior. My USB port broke completely off at the soldering And I Wanted To Wipe My Device before I send it in to insurance. Completely dead battery, I took an extra usb cable and stripped it down to the red power and black ground cables. Bottom left pin is for the Red power cable and black power cable on the bottom right pin. I used the stock Motorola usb power. I wedged the bare wires to the outside of the pins and made sure they didn't touch at all. Plugged it in and it Thankfully charged.

I just wanted to post something up in case someone else is scouring the Internet for information.

Brandon314159 said:

- You would have to watch the battery voltage at the screws for the battery flex-cable mount.

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Drat. I really didn't want to peal off the sticker... heh, maybe I could just punch through it with the needle probes and only leave 2 tiny holes .

There are lots of notes about the battery voltage being 'high' by peoples viewpoints. If you search around, someone explains the difference in chemistry that the Droid 4 is using and that it does have a higher Vmax during bulk/absorption charge levels. I believe the summary was that it is a non-issue. They aren't trying to 'cheat' the battery into higher voltage for more cap...it's just simply how that chemistry wants to be charged. You'll have to google around to find it.

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I have done a lot of googling and failed. I'm skeptical that I can't find any "new Li-ion chemistry". The only thing I did find was a pointer to an Anandtech article where the writer said he "heard" they were using a "new Li-ion chemistry" ... with no references or cites. In any event I agree it is mostly a non-issue for most everyone else. I figure they have it all designed for some target duty cycle -- probably about 1 year? maybe 2? Thing is, I plan to keep my phone for 4 or more years like all my past smart phones. The difference this time is that the battery is non-removeable (yes, I know it can be done with tools and some risk). I was hoping to find an app that would interface with the battery management and allow a configurable threshold for the "fully charged" cutoff. With a charging cutoff at about 90% I should be able to triple the life of my battery.

sigh... sorry for the hijack (but there isn't much on the actually battery operation, even around here).