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[update apr.16] Non stop working solar powered HD2

Ok guys, so nuclear war stroke the planet, your brand new tv and pc got busted in the initial attack and you're left with your precious HD2 running some custom rom and about 16-32gb of storage. Hope you don't get borred, there won't be many apps on marketplace, or even a marketplace (servers got busted by the nuke )
Now to get more seriously i can't figure out why i would need a phone able to be powered on 24/24. But i guess at least it could be useful on camping trips or stuff like this.
This is the start of a project, are goals are something like this:
1. reverse engineer the charge algorithm used by HD2 (in involves at least 2 charging modes each with 2 stages, as i know so far)
2. assemble or buy a 5-10W solar panel (only the panel and a Schottky type fast diode)
3. get myself some old laptop batteries and strip them down for cells and controllers.
4. design and assemble a cell pack as a buffer between the solar panel and phone
5. design a switching mode voltage stabilizer and make a custom usb hub in order to also have usb host functionality if i feel geeky and need linux
6. design a charge controller for the cell pack when using solar power.
7. put all things together and test
The goal is simple. Although there are solar batteries that provide some extra juice to laptops or pda's they function somewhat like 2-3 hours discharge, about one day in full sun to recharge.
I want a system that can power a full load working hd2 (worst scenario) non stop (day and night) including cloudy days, nuclear winter or whatever. The system must also be able to power about 3-4 usb devices and sustain a full 500mA drain on each port while still being able to power the hd2 non stop. Aaah, yes, the thing must be portable, plug&play, reliable and maintenance free. At most, it should have the size of a regular 15 inch laptop and about 2kg weight (all things included).

Stage 1 completed
So i figured out how hd2 charges it's battery. It's pretty simple actually.
Charging is made in the same way for either wall charger or usb charging. Same pins are used. However, when the wall charger is used, charging current can be as high as 800-900mA. This will decrease to some 20-30mA when the battery will be almost 100% charged.
If you however connect the usb data pins to hd2 and to something (computer, hub etc) hd2 will change the charging mode to usb. This feature ensures that when connected to a pc, the phone will never try to get 8-900mA from a 500mA usb port pretty neat. Instead, maximum charge current is limited to about 400mA.
If you get access to the usb wires inside the cable you can trigger either mode by simply disconnecting or reconnecting the data pins (green+white on standard usb cables). This is useful because i can devise some means of redirecting the charge current to either external battery (let's say after a night of use for the hd2) or to the hd2 if .. for some reason it's internal battery is discharged.
A usb enabled pic microcontroller (say 18f2550) can be used to control the charging process of either internal or external battery by simulating a pc connection, thus enabling hd2 to switch to low current charge. However if i'm guessing right, a simple usb hub could also do the job as it also contains a microcontoller that "knows" the usb protocol. So because i will use an external powered hub for linux, I'll try to use it also for switching between charging modes. Besides is more easier this way and i (or others) will be spared the time needed to program a microcontroller, or fabricate a pcb for it and it's corresponding components. And.. in case of nuclear attack there won't be any radio shack or electronics store where you could buy microcontrollers
Stage 2 completed:
Well i got myself some time ago a cheap 10watt polycrystaline solar panel for use with a robot i'm building. It was about $50 here in Romania. I guess i'll be using this one, even if it's quite big (something like a 16 inch laptop). Anyway i could also power other things with it. Will do some tests, and if it's suited for the job, it will be used. It arrived completely assembled so it also spares me the trouble and time of connecting individual cells into to form a solar panel.
Update : completed, will use the spare 10watt panel, until a new one arrives.
Stage 3 completed:
Got some 5-6 old laptop batteries. Stripped them down and got some ~30 cells. I'll test them out and sort about 4-6 of them.
Stage 4 completed: I'm currently sorting out some cells. As far as design goes, the capacity of the "extended battery" will be 14400mAh (single charge, using no solar power). That could easily power a full 15 inch laptop for about 4 hours, so i guess hd2 will have no problems staying alive for one night until next day and the sunrise to kick in for the solar charging to take place
Stage 5+6 completed:
There won't be any linear voltage stabilizer design for the buffer between the battery and hd2. They are quite inefficient with 30-40% power lost in the form of heat. Switching mode stabilizers+converters will be the way for this design. Found a ready made voltage stabilizer (converter) that's suited for the job , Saved some good hours that would otherwise have been spent on designing one from available parts.
Stage 7: yep, i'm now building the damn thing. I've simplified the design as much as i could, while keeping it safe for the phone, i guess the project will be possible to make by anyone with basic soldering skills.
apr. 13 - update: construction delayed due to one cell failure (the difference in internal resistance between the cells was greater then i expected). Will now search for a replacement, recalibrate the battery pack and recharge. However I expect that the battery module should be ready by the end of this day or tomorrow.

ok then.. it was built, it was tested and i'm already using it or at least.. trying to figure out a use for it
Anyway, if you're the camping type, if you feel geeky or wanna make a eco-friendly charger for the hd2 (or other usb charging enabled things) here's how to build one
You'll need the following materials:
- patience, this is a long post, try not to get bored while reading it
- some basic electronics skills, basic understanding of components, measurements and circuit troubleshooting (this is not a beginner project i guess, as hard as i tried to make it, if done improperly... well of course, you risk killing the poor phone in the process).
- some second hand laptop batteries, 3-4 would be ideal, they can be kind of old, but must be functional to some degree.
- a cheap usb charger used for cars, the one that plugs into the cigarette jack OR some good electronics skills to design a switching power supply. Guess most of people will go with the first option, in order to be more helpful i also designed this circuit using this option. You should buy the cheapest adapter, the cheaper the better. That's because the expensive ones have a feature that enables them to stop working if the voltage of the car battery drops to a certain point. That's supposed to be some sort of protection not to allow the car battery to discharge and thus preventing you to start your car. We don't want this protection, we want to be cheap asses, we want dirt cheap. However the adapter you want to buy must deliver 5V at around 1-1.5Amps minimum. 5Volts at 500mA is to little, it will simply kill itself when you start the thing once it's completed.
- a standard usb hub, any will do. This is if you want usb host functionality or use linux.
- a 5-10W solar panel. The bigger the better - it will allow to recharge the buffer battery (the one you'll be building) at a faster rate. This is the single most expensive part of this build. If you simply want an external battery for the hd2 you can skip the panel, if you want solar charging.. this is .. of course, a must.
- one fast rectifier diode or a schottky diode, you should buy it if you use a solar panel, the supplier of solar panel could also recommend one to use with that specific panel. We have to use one, this will make sure the current goes from the panel to the battery, not the other way around.
- bunch of wires, a multimeter and a soldering tool witch you're not afraid to use.
- a variable power supply, either it be a wall charger with variable output voltage, a laboratory power supply, or some charger that can output anywhere from 3.6 to 4.5 volts at anywhere from 300mA to 1A. Any combination will do. This is required only once in order to precharge the cells to a specific voltage.
- one switch or something similar in order to ... switch the thing on and off.
- spare time/understanding wife/coffee etc
1. Ok, first of all you need to get those laptop batteries open. Use some sharp tool, your karate skills or whatever necessary to crack those batteries open and expose the individual cells inside. Be careful not to damage the cells in the process, at least if you use some sharp tools. Once exposed, the cells will be linked to each other, you need to separate them by cutting the wires or metal bands that links them. Once done sort them out, if you have multiple batteries, sort the cells from each battery in a different case or basket or whatever you want, the idea is not to mix them.
Here's mine:
2. You now need to measure up individual cells with a multimeter. You're looking for the voltage rating of each cell. If you find cells with 0 volts, they're dead. If you place the multimeter in continuity testing mode and the 0 volts cells are showing continuity across their leads, yep.. they're really dead. Never use these. Good cells have anywhere from 1volt to 3-4volts.
Once you selected your good cells start forming a pack. The idea is simple. The more cells you put, the longer the thing will last. Standard laptop cells are rated to a minimum of 3.7Volts and 2400mAh. Each of them is almost double the capacity of the standard battery that comes with the HD2. However since you're going to use second-hand ones, they will have sign of usage, a smaller capacity then that of a new one. Still they will perform at least the same as hd2 battery in terms of battery life. Minimum configuration starts with 2 cells, i recommend 4 cells as a decent start but you can go and add more cells if you like. The more cells the longer battery life but at the expense of added weight. My choice was 6 cells. If you had 2 laptop batteries and each of them had 6 cells, you can make your pack on anywhere from 2 to 12 cells.
Let's say you choose 6 cells (always an even number). If 6 is you choice, you will need to divide that number by 2. So you get 3. You need 3 working cells from the same laptop battery to form a pair. Go back to the place you kept the cells and select 3 cells, NEVER mix cells from different batteries. These 3 cells you have (first pair) will need to be linked in parallel connection. The negative ( - ) of each cell is linked to the negative of the other and the positive to the other 2 cell's positive. We'll get there, but at a future step. Now we need the second pair of 3 cells. Again look in your cell basket and try to find 3 more cells from the same battery. This battery may be different then that first one you selected cells for the first pair. Yet again, the 3 cells must come from a single battery, no mixes. And.... again, these 3 cells must be placed in parallel. So if we already imagine them connected, we would have 2 pairs, each of them with 3 cells linked in parallel. The 2 pairs must be linked in series, so the minus of one pair will go to the plus (positive pins) of the other. The unconnected pins of each pairs (one minus one plus) will be used for voltage supply - you'll get the combined voltage of the cell pack here. If i were to draw this things for you to better understand.. it would look something like this.
green is one cell pair, orange the other. The black things are wires. This are the connections for a 6 cell pack. If you have 8 cells, you will make pairs from 4 cells (2 pairs). If you have 4 cells - the pairs will have 2 cells. A charged cell will have something like 4 volts. A pair made up of several cells in parallel will still have 4 volts across it's leads, but the overall current capacity of the pair is increased by the number of cells it contains. So if you have 3 cells each with 4v and 2200mAh, the pair will have 4 volts but with 6600mAh. If you place 2 pairs in series like on that drawing, you increase the voltage of the group by the number of pairs you add while still having the same current capacity. So if you get 2 pairs of 4 volts and 6600mAh, you will have 1 group, 8 volts and still 6600mAh. That's the total output of your pack. Because hd2 needs 5V (not 8 !!) we need something to decrease the voltage from 8 to 5 volts. That's why we need that car usb charger. It normally uses the 12V available at the cigarette jack to output 5v your phone can use. Cheaper ones, can use 8 volts, or 7 volts (lower voltages) because they don't have a circuit to prevent deep discharging the car battery like expensive one have. We need one without this circuit, because our battery pack only outputs 8V. So the car usb charger will take the 8 volts at it's input and give us 5volts at output.
3. before linking cells to each other, you need to charge them to the same voltage. Use a charger/power supply etc. I used a lab. variable power supply, if i had none, my weapon of choice would be a nokia standard wall charger (or another brand), older ones, i would cut off it's jack, expose the wires and connect them to my cells, it outputs 3.7 volts, enough to charge each cell. So charge each cell to about 3.7 volts. You will need to connect the multimeter in parallel to the cell and monitor the charging process. When a cell reaches 3.7 V disconnect it and charge another one, until all of them have 3.7 V. After this, leave the cells for one day. Next day you will be measuring each cell again. If one of them drops charge by it's own and you find.. let's say 3 V, you got a defective one, back to step 1&2 and select other cell pairs. If all cells still have the same aprox. level (somewhere around 3.5 to 3.7 volts) you're good to go.
Here's one cell linked to my voltage supply.
4. start thinking of either a case of something to contain your build. I used copper plated pcb (from electronics stores, radio shack etc). I will be connecting my cells to this thing, kind of like a pcb assembly. You may use some plastic housing and connect the cells with wires and secure them with some glue. If you have experience working with pcb, etching the copper layer and such things, feel free to try using pcb.
Here's my blank pcb for this job - i've already cut it to required dimensions. It's the orange metallic thing in the center. Beside it you can see my hub and the usb car adapter i will use.
5. disassemble (i repeat disassemble.. no more karate skills) your hub (if you're going to use one) and your car usb adapter. My usb adapter looks something like this.
The hub interior will look different, we'll get on that on a later step. Anyway, speaking of the usb car adapter, i'll be needing that small pcb with the components, so i'll remove it from there. The board contains the switching mode voltage converter, yummy yummy, i want that. It basically has 1 chip that generates a pulse signal that is feed to the input of a power transistor which pulses the input voltage across a coil. By autoinduction the coil produces another current, other components rectify and filter it so the second smaller current, produced by the coil, it's basically what powers on the devices connected at the output. In simple terms .. that's how it works. Again.. we need this, don't break it
Mine has a funny oval shaped form, so i'll be cutting my pcb in order to insert it inside.
There are 2 wires coming out of the small board inside. That's were the cigarette jack was connected. We will connect our cell pack to that, so you might wanna remember their position. The red one will be the positive one, black being negative. In a cigarette jack, the center pin is always positive, so if your wires have other colors, the one that's linked to the center pin will be the positive one.
6. Look for a way to place the cells inside your casing or on your pcb. Since i will do a pcb with them, i'm trying to find a possible placement for them.
this was one way, but i figured it was easier for me to simply place each pair on a line and form 2 single lines of cells instead of 3. Once done, i begun drawing the pcb with some paint marker. I will then etch the pcb, so only the paint covered areas will remain.
here's the pcb after etching, i'm connecting various wires to complete the cell pack circuit before connecting the cell themselves.
If you're using some sort of case, it's time to begin assembling your cells together. Use the solder gun or whatever you have for soldering to attach some wires to the each cell leads. Li-ion and heat aren't good friends, be as quick as possible when soldering, you don't want to heat up the cell too much. If it starts to make any strange noise, hiss or is venting anything from it... run away, don't touch it, don't throw it.. simply leave it and run away. Of course, this is a very rare scenario.. but take your safety when working with high reactivity materials like li-ion cells.
You want to arrange the cells in that paint draw up in the post. 2 pairs, linked in series. First solder wires to make one pair, then the other, then connect the pairs to each other. If you use a case, use some insulator to cover the solder points and to avoid some accidental short circuits in the future.
Back to my pcb solution, here's my assembly.
7. If you want to use an usb hub, you can try to salvage some usb port from an old pc or laptop's motherboard. This way you could avoid using a permanently attached wire to the device you're building in order to have the hub connected to the phone. I found an old laptop motherboard with an intact usb jack.
i remove the usb port from it and soldered on my board.
8. Next you need to connect the car usb charger's pcb to the battery pack you assembled. Basically the 2 wires from the charger must be linked with the 2 wires from the battery pack. Insert a switch on the cable in order to be able to turn on and off the whole thing. In my case, i'll now connect the car charger's pcb to my pcb, in the portion i've cut.
9. now you need to modify your hub to be able to power on hd2 during usb hosting mode. There's a link in the linux section (ubuntu for hd2) about this, you may want to read that also. I basically soldered a wire across each hub's usb port positive pin (the 4 usb jacks) and the input usb jack. The ground connection is the same for all jacks. So all jacks including the one used for connecting to a usb host device (pc) have the power pins linked together. Those 2 power pins must also be linked to the output of the usb car charger so that when you power up the thing using the switch, the charger also powers up the usb hub. After you solder all the wires, also insulate the soldering points and secure the hub in your casing along with the battery pack and usb car charger's pcb.
Here's mine, it was soldered on my pcb.
as you can see, there are some couple of wires coming out from it. Those need to be connected to the phone for me to have usb host functionality. So i'll connect these wires to the usb port i've mounted at step 7 so i can use a standard usb - microusb cable to link this thing to the phone. If you want to make it simpler, cut out a usb - microusb cable and directly solder the wires onto the hub's pcb as shown in the guide on the ubuntu linux thread for hd2.
In my case, i use that port i salvaged, as i said before.
10. assemble the whole thing and carefull inspect the connections. The order of this will be - battery pack - linked to the car usb charger - that's linked to the hub power pins (for each usb port). You'll then have one usb port for use when requiring usb host functionality, 4 usb ports for connecting all sort of usb slave devices, and one usb port (the one that it's soldered to the car usb charger) for use when you want to simply charge your device normally.
Here's my build. I've also placed a fuse between the battery and the usb charger, so that in case of malfunction it breaks the circuit. The fuse holding pin is the black thing at the opposite side of the usb hub. Near the pcb, you can see the fuse and it's cap.
11. Check again all connections. when ready, press the switch and bring the thing to life. Use the multimeter and check all usb ports voltage. You shoudn't have more then 5.5Volts and no less then 4.5Volts. If you do, then you did something wrong, turn off, disassemble and recheck. If you did it right, you'll get a voltage inside the above interval. Inspect the device once again and make sure all things are safely placed and secured inside. Try plugging some cheap usb devices you may have, a mouse, usb flashlight, another hub etc. If they receive power and all it's ok you may try to connect the phone.
Voila.. usb charging from the ghetto style external battery.
And here's a small video of preliminary testing (i haven't yet tested the usb hosting capability but i have no reason to think it will not work). At this time i didn't placed any switch on the board so i switch on and off the thing by placing the fuse inside the holder or removing it
http://www.youtube.com/watch?v=yf6kRpNNqkw
Next step... maybe some of you may think.. well how does this thing recharge when the batteries are depleted. At this stage the battery pack is recharged by connecting a 8.4 voltage supply across the battery pack leads (wires) but the next logical step will be adding the solar panel to the build and securing this pcb to the back of the panel. Then.. further testing. I'll be keeping the panel and that rectifier diode handy. This is still work in progress.

When are we getting it?

i guess it will take about 1-2 weeks to do the job.
i'm also involved in 2 more projects, it could be done as soon as i finish my automatic dog feeder with video-streaming over internet, food sensors and audio feedback. )

facdemol said:
i guess it will take about 1-2 weeks to do the job.
i'm also involved in 2 more projects, it could be done as soon as i finish my automatic dog feeder with video-streaming over internet, food sensors and audio feedback. )
Click to expand...
Click to collapse
Hey facdemol I am not as versed in electronics as you are my friend. So my question to you is this is something that someone with a fair level of intelligents can attempt also? Secound is this, is the list you give in your first post all some one needs to try this? I would really like try this myself and maybe correspond my findings with you. Also thank you totally of you ammazing knowledge filled posts here on XDA.

lol.... Im not sure how to respond to this
Cant wait to see how it turns out, best of luck

sounds interesting!

Good man, keep us updated however things turn out... you sound like someone who isn't afraid of experimenting with electronics for the thrill!
Sent from my Nexus One

Wow! Pretty interesting

Hey facdemol I thought you might like to check this article in the Portal out if you have not already. Looking forward to hearing back from you here on your project.

good article, was inspiring
stage 2 and 3 are completed. Now working to design a high performance dc-dc (switching mode) converter that would take 8.4V input and give me some 5V @ 2.5A output for hd2's charging and the usb hub. Some work needs to be done here and some careful testing, if for whatever reason this converter fails, hd2 motherboard could get fried Working on a way to implement some safeties, also i'm studying the way older pda's and pna's used switching mode power supply's and converters. I'm thinking i could either salvage one of these modules or build one specifically for hd2.

Update : found a way to make this pretty DIY for anyone with basic electronics skill (so that you can avoid designing switching mode converters, making PCB's, winding coils etc).
I found some dirt cheap car adapters that output 5v (pc usb jack) and can be used for various usb charging enabled devices. I'm testing to see their performance with my custom battery pack and the solar panel. Results are pretty good so far, i managed to run them stable at arout 5.5-6Volts input voltage. 2 of these will be required for this project (2 amp max current) or one if the output transistor inside is changed or a heatsink is mounted on it. I will come back with results and in the end, a guide with the required modifications.

The second post contains the updated progress on this project.
Third post will contain some sort of guide for a DIY assembly of such device.
These are updated daily.
If everything goes smooth, i guess i will posting some pictures and guides to build such things, by the end of this day or tomorrow.
Current features of this design :
- 10watt solar panel module
- 14400mAh battery module - cell pack designed as 3p2s
- 2 charge modes (slow - similar to a pc's usb port and fast - similar to hd's wall charger)
- 4 powered usb ports (usb host capable)
- 1 high-power usb port (it can charge any device requiring 5V at around 500mA - 1500mA)
- uses standard usb-microusb cables, no need for other hacks or special cables
- feels geeky

facdemol said:
The second post contains the updated progress on this project.
Third post will contain some sort of guide for a DIY assembly of such device.
These are updated daily.
If everything goes smooth, i guess i will posting some pictures and guides to build such things, by the end of this day or tomorrow.
Click to expand...
Click to collapse
Sounds greet I will bee waiting to see what you have come up with man, this could be something that can change how we can use our HD2s on the go. n
Keep up the good work facdemol, I am also waiting to see if you post any more power consumption results in your other thread.
I would like to ask anyone reading this to help vote this to be published in the XDA portal by clicking the vote bottom at the top right of the first post by facdemol, he deserves recognition for his great work with this project and his others.

Very Interesting ! Good luck with the project! will be following to see what develops!

I love this. Great concept.

it took a while to charge the independent cells to the same level and to form a pack. The charge alignment is a must, otherwise, the battery back will discharge at an uneven rate among each cell. One done properly it should allow the maximum battery life and no future maintenance.
I've done some testing on it, already hooked up the hd2 to this thing, it's working properly, both charging modes, usb host etc. I guess i'll come back today with the guide and pictures to make this, it took the better part of yesterday to manually charge/discharge each of the 6 cells in the pack.

updated post 3, half of the buid is already done and operational. The battery and hub+charger module needs to be linked up to the solar panel and some of case to be built.
There are some pics and one video with the thing working. Just basic testing for now, i just finished it.

Very interesting...great job mate...

[Q] N7 discharging when plugged in

Lately – I’m not sure when this stated, my Nexus 7 (running 4.4.2) has been charging absurdly slow. I’m talking 20%-30% in a span of 24 hours. It’s like it’s hooked up to a trickle-charge. I’ve tried 2 different OEM cables and 2 different OEM chargers (I had the one that came with it, and I ordered an official Asus OEM replacement charger with cable as well, to have as a spare).
I downloaded Battery Monitor Widget and while it sees it as plugged in via AC, the charge rate is -9ma (in other words, while plugged in, running nothing but the battery monitor, instead of actually charging, it simply reduced the discharge rate from negative 718ma to negative 9ma).
The only thing I can think of is this: as I understand it, USB AC adapters capable of “fast charge” (2ma) first test the device to see if it’s compatible, to avoid potentially over-charging the unit. Perhaps my device is not properly responding to this test? Perhaps that’s why it’s not providing enough juice?
Or maybe someone else has some better insight and can educate me. I’m certainly open to learning. Any ideas?

WraithTDK said:
The only thing I can think of is this: as I understand it, USB AC adapters capable of “fast charge” (2ma) first test the device to see if it’s compatible, to avoid potentially over-charging the unit. Perhaps my device is not properly responding to this test? Perhaps that’s why it’s not providing enough juice?
Or maybe someone else has some better insight and can educate me. I’m certainly open to learning. Any ideas?
Click to expand...
Click to collapse
[apologies in advance for a long-winded reply; hopefully some of it will be useful to you]
The OEM charger should be capable of 2 A (not 2mA).
Dumb chargers don't "talk" to the tablet. (Well, except for Apple USB dumb chargers - Apple violates the USB spec with their proprietary hardware, and that raises the meaning of "dumb" to a whole new level).
The tablet tries to draw what it wants, and if the wall charger is capable of supplying that current, everything will be fine - meaning, that the output voltage of the charger will be stable (near to 5V). If the tablet tries to draw more current from a charger than the charger is designed for, what usually happens is that the output voltage of the charger will start to droop down. (Sometimes, even worse things can happen, such as the voltage coming from the charger will start to oscillate.) This will have the effect that the voltage drops down to the point where it is barely larger than the voltage from the battery, and so the current flowing out of the charger gets limited that way.
But you shouldn't have this problem as you have at least two OEM chargers, and more than one cable, suggesting that your difficulty is with the tablet somehow.
I note (from your post) that you can observe the actual charging current; this suggests that you have a custom kernel on your tablet, as the stock kernel doesn't have the BQ27541 patches which allow current monitoring (only battery voltage and percent charge).
Here's the reason why I mention this. (Oh boy, get yourself a beverage, this is a long story).
I was going to be making some long drives (>13 hr) and I wanted my N7 in the vehicle, WiFi tethered and active (Google Nav and so forth) As you have observed, when you have the tablet running and are poking away at the screen, it can draw anywhere from 300 mA to more than 1000 mA, depending on how many cores are alive, which CPU frequency is in use, the screen brightness, streaming activity, etc.
And unfortunately...I was in a hurry: I couldn't wait for a car charger to be delivered following an online purchase. And all the local electronics stores seem to only sell high-capacity car chargers that are "Apple Compatible", which is marketing speak for "violates the USB spec". The N7 expects compliant behavior from chargers.
So, I bought two of those "Apple Compatible" car chargers from different manufacturers, and also bought a micro-USB cable that I could hack. I opened up the cable, clipped the D+/D- wires, connecting them together on the "Nexus 7" end of the cable, and left them open on the charger side (open but insulated of course). This has the effect of preventing the N7 from thinking there is a data connection present - the Apple chargers twiddle those D+/D- lines a little bit, and that prevents the (USB spec-compliant) N7 from thinking there is a dumb charger on the other end of the cable.
I wanted to be sure that what I had was actually working correctly, and if either of those two car chargers really would provide enough current, so I installed a dev kernel that has the BQ27451 battery current monitor patches in it. I think several of the dev kernels have this; I used M-kernel.
OK, so far so good.
The next step was to crank both the min and max CPU clock limits way down (300 Mhz iirc), turn on the "performance" governor and turn the screen brightness all the way down. I may have even used Trickster Mod to set Max_Cores to only 1. This was done so that the tablet would draw a smallish and constant current. That way, when I plugged in the car charger, I would actually know what the total charger current was - the sum of the (absolute) values between the unplugged state (discharging) and plugged in (charging)** If you leave the CPU frequency controls in their normal state, the amount of current the tablet draws can jump all over the place depending on tablet activity, and then it would be hard to know the total current the charger is actually producing. (It is the SUM of the battery current displayed plus whatever the tablet is drawing).
When I did the above, my N7 (grouper, WiFi off) was drawing just under 300 mA of current from the battery in the unplugged condition.
Still with me? (it gets better, trust me).
So, what I observed was that, yes, one of the two chargers was better than the other; I could get get the monitored battery charging current up to 1400 mA with one, and maybe 1100 mA with the other. (That's total current from each charger of about 1.7A or 1.4A respectively after adding in the 300 mA the tablet is drawing)
Finally though, an explanation of why this is relevant to you:
When the tablet was plugged in to either charger, the current would not immediately jump up to the maximum value; instead, it would sometimes takes minutes or more for the current to jump up to that maximum value!
It would, however immediately jump up to about 800 mA total current right after plugging the charger. That's better than a 500 mA computer USB connection, but if the tablet is active, it's no guarantee that the tablet will gain any charge - as in your situation.
So why the delay? To be honest, I don't really know. In my panic to get ready for my travel, I only spent a little bit of time fooling with it - for a while I had a hypothesis that the kernel was doing *something* that made the current pop up to its full 1.7A value only after the tablet had left a deep sleep state. The good thing was that once the current stepped up to the full value, it would stay there despite the level of activity on the tablet.
[size=+1]The point is that the maximum charging current condition seems to be dependent on some condition(s) happening which is under control of the kernel - it is not just an "analog" behavior that happens as soon as you plug the charger in.[/size].
So I suppose it is possible that you simply have a configuration where the operating trajectory that your tablet passes through does not trigger the right conditions in the kernel to command the SMB chip (USB interface controller) to max the current out close to the 2A limit.
You might want to try an experiment where you:
- Observe the charging rate with the tablet completely turned off. Should be about 100% in 150 minutes (2.5 hrs) or about 6-7% every ten minutes. Note that because the battery is 4.235 A-h capacity, that works out to a charging current of at least (4.235 A-hr / 2.5 hr) = 1.7 A. (It is probably greater than that due to charging losses).
If your tablet charges at about this rate when it is off, then nothing is wrong with your charger, cable, battery, or SMB chip, and it points a finger at your kernel's code - and possibly other things like applications holding wakelocks which prevent the tablet from entering deep sleep.
I won't go so far as to claim that it is "coming out of deep sleep" that triggered the M-kernel to twiddle the SMB chip so it would draw 2A; in all my experimentation, I couldn't faithfully reproduce the behavior. The good news was that that it would eventually (within a few minutes, possibly due to the tablet sleeping) ramp completely up and then stay there.
Anyway, I hope this gives you some food for thought and maybe some experiments you can run to narrow down the problem.
- What kernel are you using?
- Does your tablet ever enter deep sleep? (I don't mean simply that the screen is off - it is a state where the hardware is placed in a low-power state where even the memory bus is no longer operating. A wakelock might prevent this from happening, but in any event you should be able to observe this in the kernel log - the clock values get wonky and you might see a message about "G" state)
- Does your tablet charge even a little bit when the screen is off?
** I sort of recall that that "Current Widget" app always displays a positive value for current, but changes the display color red/green depending on whether the tablet is discharging (red) or charging (green). Something to watch out for.
.

Kernel: It's rooted, but otherwise completely stock. Battery Monitor Widget doesn't seem to have an issue display the charging rate (and yes, I meant 2A, not 2ma).
Sleep mode: It should; I have one of those cases whose covers are supposed to put it in sleep mode. It DOES charge; but it does it at a snail's pace; a battery info app has it at 30% over the span of 24 hours with it never being touched during that time.
I turned it completely off 3 hours ago at 37% and I just turned it on to 76%
Unfortunately, Current Widget is not compatible with the N7.

WraithTDK said:
Kernel: It's rooted, but otherwise completely stock. Battery Monitor Widget doesn't seem to have an issue display the charging rate (and yes, I meant 2A, not 2ma).
Click to expand...
Click to collapse
It actually displays instantaneous current? Maybe I should restore a 4.4.2 ROM and see if the newer stock kernel has those BQ27541 patches.
WraithTDK said:
Sleep mode: It should; I have one of those cases whose covers are supposed to put it in sleep mode.
Click to expand...
Click to collapse
Well, "screen off" is not equal to "deep sleep". The tegra3 has multiple low-power modes, but the one I am thinking of is really low power - kind of like a "suspend" state for PCs. If there is an application holding a wakelock, the tablet will never enter deep sleep. (As I mentioned, the "deep sleep" mode is very near to the tablet being completely off - the lpRAM is still drawing a little bit of current (it is in self-refresh mode) ). When my N7 sleeps, it charges nearly at the same rate as when it is turned off. (But, see below; in light of that I don't think this is your problem)
WraithTDK said:
It DOES charge; but it does it at a snail's pace; a battery info app has it at 30% over the span of 24 hours with it never being touched during that time.
I turned it completely off 3 hours ago at 37% and I just turned it on to 76%
Click to expand...
Click to collapse
39% in 3 hrs? Hmmm. If things were linear, that would be: 0.39*4.235 / 3 = 551 mA.
You are right, that isn't very good at all. Your tablet will discharge if you are using it even though it is plugged in.
Well - that "tablet off" charging test is pretty diagnostic - the kernel and OS are not even running, so they can't be altering anything. So maybe they can't be blamed for anything either.
But, that Summit Microsystems SMB347 chip is sitting there acting as the battery charger, even when the tablet is "off". Maybe it has something stateful in it (like a few non-volatile memory registers) that could have been altered by past activity on the tablet. Summit doesn't allow datasheet downloads without a NDA, so I don't know.
When the N7 is fully turned off, there is still something tiny running - otherwise, how would that "charging animation" get painted on the screen when you plug the tablet in when it is off? I don't know if that is something in the tegra3 miniloader or just a low-power personality of the bootloader; hard to know really. I guess I am speculating whether something in the bootloader could have "programmed" the SMB chip, but the only thing I remember seeing here (on XDA) is a toggle via a fastboot OEM command that causes the tablet to boot up as soon as power is applied - the guys who do car installs use that.
Well, I'm sort of out of ideas. It sounds like you have tried the obvious stuff already. Do you have any reason to believe the USB port has an intermittent connetion? Or maybe that the battery itself has an intermittent or resistive connection at its power connector?
cheers

Had a very similar problem on my s3 and the problem was the microusb port on the phone
Sent from my SPH-L710 using Tapatalk

WraithTDK said:
Lately – I’m not sure when this stated, my Nexus 7 (running 4.4.2) has been charging absurdly slow. I’m talking 20%-30% in a span of 24 hours. It’s like it’s hooked up to a trickle-charge. I’ve tried 2 different OEM cables and 2 different OEM chargers (I had the one that came with it, and I ordered an official Asus OEM replacement charger with cable as well, to have as a spare).
I downloaded Battery Monitor Widget and while it sees it as plugged in via AC, the charge rate is -9ma (in other words, while plugged in, running nothing but the battery monitor, instead of actually charging, it simply reduced the discharge rate from negative 718ma to negative 9ma).
The only thing I can think of is this: as I understand it, USB AC adapters capable of “fast charge” (2ma) first test the device to see if it’s compatible, to avoid potentially over-charging the unit. Perhaps my device is not properly responding to this test? Perhaps that’s why it’s not providing enough juice?
Or maybe someone else has some better insight and can educate me. I’m certainly open to learning. Any ideas?
Click to expand...
Click to collapse
You might have an issue with your USB on your device. Mine was starting to charge slow but not quite to the degree as yours. I also found that my device would no longer communicate to any computer. If you have tried different cables & charger then you may have to RMA your device.

Asus Nexus 7 draining while plugged in to charge
My Nexus 7 was totally dead. Hit the power button and five blinks of a white LED. Plugged it in it went to 68% then next day it was 28% - 19% and on down. Before it got to zero I turned it off and took off the back. I noticed with the aid of a magnifying glass, that the soldered connections of the mini USB charging port were very possibly fractured. Having had experience at soldering, I added solder and reflowed the connections (about 4 or 5). I then plugged it in. For the first time since the beginning of this mystery I saw the battery icon actually indicating that it was charging. It was 100% within three hours. Haven't had a problem since.
I have been searching all over and found many ideas from - try another charger to - install another charging board. When you think about it, that connecter sees a lot of push and pull. If it is not soldered well and sturdy it's no wonder that it will fracture. I don't think there was enough solder on there to begin with.
If you do not know someone who can solder on a very small scale and want to brave this yourself, make sure you have a very small tip on the iron, not more than 700 degrees and some extra flux. You will most likely bridge a few connectors but keep brushing the tip of the iron away from the connections with flux added. You will get it eventually. Just don't burn the board. And clean it all with a brush and alcohol. Good luck.

Black screen with white streaks when powering up then black

I have been reading all the posts regarding the dreaded "black screen" issue. However mine doesn't seem to fit the bill
It has been left to discharge and wouldn't boot up. i plugged it in (wall charger) and left it for 24hrs. I tried to boot it up but all that comes on is the Google logo then i see some white video streaks then it turns black again
It is rooted and i tried to boot into TWRP but it shows the same streaks then it turns black again. I did press on the back where the connector was supposed to be and thinking would fix it but no success
I do not know what else to do.
Do i need a new screen? I wouldn't mind to replace it if i knew that was the problem but i am not sure if that is the case
Is there anyone that had a similar experience and can maybe share some ideas?
I would really appreciate it!!
Thank you

rainfactor said:
...regarding the dreaded "black screen" issue. However mine doesn't seem to fit the bill
It has been left to discharge and wouldn't boot up.
Click to expand...
Click to collapse
I was under the impression that that scenario is exactly the bill - the battery drains off to such a low voltage that the internal charge controller circuit doesn't work correctly at that low voltage, even when you put the device back on the charger, so you are stuck with a not-dead unit that won't turn on, and also won't take a charge. (But that hardware isn't dead - you just need a partial charge on the battery to get the charge circuit to start working again.)
The only recourse really is to get a *small* amount of charge on the battery by some means other than the built in charger, and then reconnect the battery to the tablet and put it on the charger to complete the charging.
There are disassembly instructions on here that take you through the steps necessary to get to the battery connector (it detaches and has a short run of wire between that connector & the battery so that should be convenient for attaching the battery to something else without removing the battery from the tablet). Use the search functions.
If you can borrow a voltmeter, the symptom will be obvious: a very discharged battery will have a terminal voltage around 3.0v (maybe less). Under normal conditions the battery voltage will rise to about 4.05v when fully charged (measured when disconnected from the charger) and be somewhere around 3v when completely discharged.
Don't do anything stupid (there are examples of that on here too). The charger that you use needs to limit the amount of current to a reasonable value, say less than 500 mA. The battery can tolerate up to about 1.8 Amps of charging current but you should use something far more conservative than that for safety reasons. And you are only trying to put a small charge on the battery (not completely charge it) so you don't need to use the fastest possible charging rate anyway.
Something incredibly cheap would be a USB cable (with the micro-B connector cut off) and a 1/4 watt, 100 ohm resistor connected to the positive supply line coming from a 5 volt USB wall wart charger. Even if the battery was a dead short, only 50 mA of current would flow and the resistor wouldn't burn up. If the battery was good but heavily discharged, you'd only be charging at a 20 mA rate - that would put a 10% charge on the battery in ~30 hours.
If you initially measured the battery and found it had a voltage of 2.5v or higher, you could use a 22 ohm, 1/4 watt resistor safely and charge the battery 10% in only 8 hours or so.
You can charge faster by using a resistor of a higher wattage rating, but 1/4 watt size are readily available and cheap.
The equation for power dissipated in the resistor is
P > V^2/R or
R > V^2/P = (Vs- Vb)^2/P
So for example in our case with Vs = 5, Vb = 3 and a 1/4 Watt (P) resistor, we would get
R > V^2/P = (Vs- Vb)^2/P = (5-3)^2/0.25 = 16 ohms.
The "dead shorted battery" worst case would be Vb=0 or
R > (5-0)^2/0.25 = 100 ohms
(so you can see where the numbers came from)
Anyway, that's my recommendation
- disassemble to the point of exposing the battery connector
-disconnect battery from tablet
- put battery on simple & safe charging circuit (+ terminal to resistor to + terminal, and - terminal to - terminal)
- let it sit for a while*
- reconnect to tablet and finish charging
- profit
* if you leave a live circuit unattended, even if it is only a 5v circuit, please please no exposed wiring or loose connections. Use tape and plastic straws for temporary insulation... or shrink wrap if you prefer a neater look.

bftb0 said:
I was under the impression that that scenario is exactly the bill - the battery drains off to such a low voltage that the internal charge controller circuit doesn't work correctly at that low voltage, even when you put the device back on the charger, so you are stuck with a not-dead unit that won't turn on, and also won't take a charge. (But that hardware isn't dead - you just need a partial charge on the battery to get the charge circuit to start working again.)
The only recourse really is to get a *small* amount of charge on the battery by some means other than the built in charger, and then reconnect the battery to the tablet and put it on the charger to complete the charging.
There are disassembly instructions on here that take you through the steps necessary to get to the battery connector (it detaches and has a short run of wire between that connector & the battery so that should be convenient for attaching the battery to something else without removing the battery from the tablet). Use the search functions.
If you can borrow a voltmeter, the symptom will be obvious: a very discharged battery will have a terminal voltage around 3.0v (maybe less). Under normal conditions the battery voltage will rise to about 4.05v when fully charged (measured when disconnected from the charger) and be somewhere around 3v when completely discharged.
Don't do anything stupid (there are examples of that on here too). The charger that you use needs to limit the amount of current to a reasonable value, say less than 500 mA. The battery can tolerate up to about 1.8 Amps of charging current but you should use something far more conservative than that for safety reasons. And you are only trying to put a small charge on the battery (not completely charge it) so you don't need to use the fastest possible charging rate anyway.
Something incredibly cheap would be a USB cable (with the micro-B connector cut off) and a 1/4 watt, 100 ohm resistor connected to the positive supply line coming from a 5 volt USB wall wart charger. Even if the battery was a dead short, only 50 mA of current would flow and the resistor wouldn't burn up. If the battery was good but heavily discharged, you'd only be charging at a 20 mA rate - that would put a 10% charge on the battery in ~30 hours.
If you initially measured the battery and found it had a voltage of 2.5v or higher, you could use a 22 ohm, 1/4 watt resistor safely and charge the battery 10% in only 8 hours or so.
You can charge faster by using a resistor of a higher wattage rating, but 1/4 watt size are readily available and cheap.
The equation for power dissipated in the resistor is
P > V^2/R or
R > V^2/P = (Vs- Vb)^2/P
So for example in our case with Vs = 5, Vb = 3 and a 1/4 Watt (P) resistor, we would get
R > V^2/P = (Vs- Vb)^2/P = (5-3)^2/0.25 = 16 ohms.
The "dead shorted battery" worst case would be Vb=0 or
R > (5-0)^2/0.25 = 100 ohms
(so you can see where the numbers came from)
Anyway, that's my recommendation
- disassemble to the point of exposing the battery connector
-disconnect battery from tablet
- put battery on simple & safe charging circuit (+ terminal to resistor to + terminal, and - terminal to - terminal)
- let it sit for a while*
- reconnect to tablet and finish charging
- profit
* if you leave a live circuit unattended, even if it is only a 5v circuit, please please no exposed wiring or loose connections. Use tape and plastic straws for temporary insulation... or shrink wrap if you prefer a neater look.
Click to expand...
Click to collapse
Wow! THANK YOU VERY MUCH !! I did not expect such a detailed answer.
I REALLY appreciate for taking the time to answer me!
I will try the things you recommended:good::good::good:

rainfactor said:
Wow! THANK YOU VERY MUCH !! I did not expect such a detailed answer.
I REALLY appreciate for taking the time to answer me!
I will try the things you recommended:good::good::good:
Click to expand...
Click to collapse
The more information you can collect before you begin the more confidence you will have. Hopefully you have a voltmeter or can borrow one to insure you are getting the wiring polarity correct and you are not going to damage anything or cause a fire.
If the battery voltage is closer to 4v when you first crack open the device, then this hypothesis about an overly-discharged battery is not correct, and you should assume that some other mechanism is involved.
The resistor values I used as examples are just barely big enough to meet their own thermal rating (1/4 watt in the examples), so that means that they can get hot. I'm pretty sure their thermal rating is for "natural convection", meaning that you don't need to put a fan on them to keep them cool, but you shouldn't cover their bodies up with any insulation or shrink-wrap. Nor should you leave them in that state next to a pile of papers or a jug of gasoline
A more sophisticated approach would involve using an adjustable battery charger that operates near 5v (the normal wall-wart USB voltage) and will let you set the current level, but almost nobody owns one of those. (But I have plenty of dodgy USB cables that the cats have chewed on that can be sacrificed for a quick-n-dirty trickle charge exercise.)
good luck.

NST battery voltage shutdown treshold hackable?

Hi,
i use a Nook Simple Touch as typewriter with an usb-keyboard,
which works great thanks to the usb host mode app, or, automated:
an old version of tasker with a plugin to deactivate charging and activate hostmode ( and fastmode...) via shell command after booting.
The problem is, this mode drains the battery really fast,
and charging while using the keyboard, so nececessarily with OTG cable attached, is a bit of a pain in the neck,
because there is only 1 possible sequence of actions how you can enable charging with more than around 100 mA (which would be way too low in this case) while the keyboard is active,
which requires a 16k resistor between GND and ID pin, rebooting, temporarily disconnecting some wires via switch, tapping around etc etc,
(and also does not work well when the nook is completely off ),
so i decided to leave the usb port exclusively for the keyboard,
an remove the internal battery an replace it with a external big 7000mAh or so 1S li-ion pack,
which is charged externally with a lipo module
(while charging, the nook is powered by an ac adapter, power source switching is realised with a relay and a really big capactior to avoid any more complicated possibly failing electronics)
which works great and is very easy to handle,
BUT i really dont like li-ion batterys of any kind because of the fire hazard,
nimh eneloop cant be used because charging in parallel is not a good idea,
so i would like to use lifepo4 chemistry instead,
which has a working woltage between around 3 and 3,6 volts,
but the nook powers down at around 3,65 volts.
A boost/buck converter isnt possible because as the battery drains, the voltage must sink slowly for the nook to make a normal shutdown
and not crash, damage the file system etc, (and also a converter drains quite much battery even if the nook is completely off.)
Question: it would be VERY kind if anyone who has a clue about this could share his opionion on that:
is it possible (if the hardware itself can handle it) to lower the android/nook shutdown voltage to about 3 volts with some rom/software modifications ?

threshold not treshold

Wow, this all seems a bit complicated.
I had never heard of this 16K resistor stuff.
As far as I could tell, the ID pin is only sensed high or low..
Unless I'm mistaken the OMAP3621 ULPI registers only indicate high/low.
The TPS65921B (which is the actual PHY) list 90K as the typical break point.
Of course, there could be a circuit completely external to the ULPI/PHY.
Where did you find out about 16K?
Changing the voltage of everything seems the difficult way to go.
You'd have to modify uboot as well as the charger daemon.
A note: The USB charge pump is pretty inefficient, 55%.
If you were to load the USB to the maximum speced 100mA with a 3V battery, it would be drawing 303mA from the battery!
5V × 100mA / 3v / 55% = 303mA

Oh, you got me confused with your two posts.
When you were talking about ID and 16K did you mean the ID on the battery pack or the ID on the USB OTG?

Renate NST said:
Where did you find out about 16K?
Click to expand...
Click to collapse
wired a 50k pot between gnd and id pin,
in the usb mode app tapped "host" and watched if the led goes an stays on,
if not, lowered the resistance, tried again etc,
as soon it stayed on (at 16k at my device ) used this value as permanent fixed resistor.
with that otg mode keyboard use is possible,
but also at the same time the nook doesnt really believe its in otg mode so charging with 500mA is possible,
if done in this order:
- feed 5v to the + - of the usb cable
- reboot (not always required)
- remove an reinsert usb plug
- hit "host" 2 times, keyboard works and charging with around 500mA works (measured it)
but charging doesnt work when nst ist powered off,
and automount of the keyboard at startup via shell is not possible,
and cable acrobatic is required,
and as you say, usb charging is inefficient.
the other solution with an external battery (at the nst batt terminals) with external charging logic with a relay is a much easyer way,
but depends on a li-ion cell because of the 3,7-4,2 voltages the nook can use,
a lifepo4 ( or 2s li titanate + diode) would be safer and has more cycles but would require the nook
to work with 3 to 3,7 volts, which seems too complicated, changing demons etc whatever that is...
after some research it seems its not really an issue, the newer sanyo/panasonic, samsung, sony, lg powertool/ebike cells seem to be quite safe, as far as youtube shortcircuit etc tests demonstrate.
thanks for the orientational infos

Renate NST said:
Oh, you got me confused with your two posts.
When you were talking about ID and 16K did you mean the ID on the battery pack or the ID on the USB OTG?
Click to expand...
Click to collapse
sorry, i should have used one thread, i suggest ignoring the other one,
where the only request was if the nook battery terminals can survive up to 5v,
here was the request if the nook can be modified to accept at the battery terminals a voltage down to 3v and stay on.
so 3v too complicated, 5v too dangerous,
so i stick with the relay and the li-ion cell, no problem, i was just curious if an improvement would be easily possible.
the battery id resistors have nothing to to with all that, 10k and 30k work fine,
i meant the 5 pin micro usb otg connector, not shorted zero ohms as usual, but 16k.
(but thats obsolete now)

another observation: in some thread you mention you charge the nook while using an usb keyboard,
i tested it and with a normal otg cable, and the usb mode app set to 500 mA oder 1,5 A,
and a 50% charged normal internal battery,
the device draws around 250mA, and the battery gets charged very slowly, or not at all, depending on cpu usage etc.
and if the battery reaches 100% , it continues to draw around 250 mA, which is strange,
because when using a normal, non-otg usb cable,
the device draw only around 100mA when the battery had reached 100%,
so the difference must be used for heating purposes somewhere or overcharge the battery,
which might be a reason for swelling lipos.

Has anyone tried connecting 5 Volts directly to the internal battery terminals ?

Does it damage the Board or not?
I accidentally did connect 5v for a second or so,
it did power on, i disconnected immediately, and after that it didnt power on for several hours,
but not sure if it was because of the interruption during boot, or overvoltage.
Can somebody confirm?
(i cant use a diode for voltage reduction, its a bit complicated, i use a load sharing capable solar charger board etc)

its a nook simple touch

Yow, don't do that!
Ok, it should be able to take it, but still.
I've often fed 4V to devices which had their battery blow up.
In worst cases I've used a diode for drop, but the voltage can be pretty variable over load.
The uboot on most things will not continue if there is zero voltage on the battery.
Also, the peak current of a device can go up to 600 mA or more at times.
That kind of current often can't come in through the USB connector.
Finally, battery packs have ID connections and thermistor.
Entirely disconnecting a battery pack will often prevent booting even when voltage is present.
If you have a dead battery pack always keep the the connector, cable and tiny PCB inside.
Attach a power supply to where the naked cells used to connect to the PCB.
For wiring of the battery pack see: https://forum.xda-developers.com/showpost.php?p=42552349&postcount=5

thanks, 2 weeks ago i prepared to measure possible resistors but did a google search before, found your description...
i use the protection board with a 18650 3000mAh lithium manganese (to prevent blow (up)) etc cell and charge it externally,
which requires switching between charging the batt + powering the nook over the batt terminals,
and using the batt for powering the nook , all that while the usb keyboard is connected and in use,
this is done via relay and a really big capacitor, which works great but is a bit ghettostyle.
i tried to use another charger board with load sharing circuitry instead,
but the only easy available module requires 5v minimum input, passes this 5v to load if the ac adapter is plugged in,
if not, it passes the battery voltage to load,
so a diode(+ parallel resistor to maintain voltage drop) or LDO doesnt work because it would at least steal around 0,5 v,
which is to much reduction for the battery voltage, because the nst powers off at ~ 3,7v,
easiest would be to just let the 5v to the nook but seems no good idea.
anyways, it works with the relay