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Old 10-03-2012, 04:40 AM   #1
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Lightbulb K3 battery voltage? (I²C details)

I took apart my unresponsive K3 the other day, and measured the battery voltage. To my surprise there was a grand total of 0V between the '+' and '-' terminals!

There was also 2.8V between either of these and either of the SDA/SDC terminals. I'm not a stranger to I²C, and there are typically pull-up resistors on both the data and clock lines, so maybe that shouldn't be so shocking.


So, here are my questions:
  • Is it normal that there is no voltage whatsoever between the terminals of the battery? (I mean, it could be that there's some kind of I²C handshaking necessary before the battery connects it's cells to the outside world, but it sounds curious.)
  • Is it normal that the battery/kindle I²C connection works with 2.8V? (I'm more used to 3.3V, but hten I haven't worked with modern consumer electronics, where I understand that all voltages creep downwards.)
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Old 10-03-2012, 07:29 AM   #2
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Originally Posted by Popup View Post
I took apart my unresponsive K3 the other day, and measured the battery voltage. To my surprise there was a grand total of 0V between the '+' and '-' terminals!

There was also 2.8V between either of these and either of the SDA/SDC terminals. I'm not a stranger to I²C, and there are typically pull-up resistors on both the data and clock lines, so maybe that shouldn't be so shocking.


So, here are my questions:
  • Is it normal that there is no voltage whatsoever between the terminals of the battery? (I mean, it could be that there's some kind of I²C handshaking necessary before the battery connects it's cells to the outside world, but it sounds curious.)
  • Is it normal that the battery/kindle I²C connection works with 2.8V? (I'm more used to 3.3V, but hten I haven't worked with modern consumer electronics, where I understand that all voltages creep downwards.)
The battery management is on the SPI controller, not the I2C controller.

No, that is not normal - the battery terminals are battery terminals.

The full charge on the K3 battery brings it up to nearly 4.2v.

The SoC will detect a low voltage condition, slow to appox. 1/10 the normal clock speed and run at 2.8 - - -
Intended I suppose to run "just enough" to control the charger.

It is very likely that battery is dead now from over-discharge.

It is also very likely that the battery management in the Kindle will not be able to recover the battery from that discharge level, although an external Li-Ion charger might be able to do it.

If the K3 is still under warranty - send it home.
That is where mine is headed.
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Old 10-03-2012, 08:35 AM   #3
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I left it plugged in over night, and this morning I measured 3.7V over the battery terminals, which I gather is a Good Sign™.

It booted once or twice, and even let me choose a book once, but then it hung.

When plugged in to a PC it once showed up as a Kindle and once as "MX 35 / SE Blank RINGO", which I believe is a fall-back mode of the SoC.

I'll leave it plugged in for another couple of days, but it may well be that the battery is dead. If so, where can one find a trusted replacement battery? I see a bunch of them on eBay, but I'm a bit weary of buying lithium batteries from unknown sellers, as there's no way of knowing how (and how long) they've been shelved.
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Old 10-03-2012, 08:39 AM   #4
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Try for at least 4.1v (90% +)

But you may well be correct - the 'failure mode' is lowered storage capacity.
I.E: you may now have a 1.8mAh battery rather than a 1,800mAh battery.
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Old 10-03-2012, 10:09 AM   #5
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I just bought 80 K3 demos. I could sell you one with a broken screen super cheap so you could swap batteries. They even have 3G so you could debrick it and swap screens instead if you want to...

Last edited by geekmaster; 10-03-2012 at 10:23 AM.
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Old 10-03-2012, 10:36 AM   #6
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I just bought 80 K3 demos. I could sell you one with a broken screen super cheap so you could swap batteries. They even have 3G so you could debrick it and swap screens instead if you want to...
Broken screen is OK - you got one that the USB port still works?
Just in case I can't sweet talk Amazon into exchanging mine.
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Old 10-03-2012, 10:44 AM   #7
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I just bought 80 K3 demos. I could sell you one with a broken screen super cheap so you could swap batteries. They even have 3G so you could debrick it and swap screens instead if you want to...
That sounds interesting!


(Admittedly I'm in deepest Europe (Switzerland) so shipping might be exorbitant.)
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Old 10-03-2012, 10:48 AM   #8
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That sounds interesting!


(Admittedly I'm in deepest Europe (Switzerland) so shipping might be exorbitant.)
When I checked, shipping to France and GermanySwitzerland were less than $15, so Switzerland would probably not be that much different. Current postal regs prevent shipping a bare (or end-user removable) lithium battery except when shipped from the factory. It needs to be integrated into a device (such as a kindle) to ship it internationally. I will be shipping some Paperwhites internationally soon. And a couple of K4 demos too.

Last edited by geekmaster; 10-11-2012 at 09:12 AM.
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Old 10-03-2012, 11:03 AM   #9
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Originally Posted by geekmaster View Post
When I checked, shipping to France and Germany were less than $15, so Switzerland would probably not be that much different. Current postal regs prevent shipping a bare (or end-user removable) lithium battery except when shipped from the factory. It needs to be integrated into a device (such as a kindle) to ship it internationally. I will be shipping some Paperwhites internationally soon. And a couple of K4 demos too.
Sounds pretty reasonable.
And if you have to ship it inside a kindle, why not make it worthwhile? How much would you want for a 3G with broken screen?

(I believe that it would be possible to swap screens from my old device? If these are demo-units, is it still possible to de-brick them and register with Amazon?)
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Old 10-03-2012, 11:07 AM   #10
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Sounds pretty reasonable.
And if you have to ship it inside a kindle, why not make it worthwhile? How much would you want for a 3G with broken screen?

(I believe that it would be possible to swap screens from my old device? If these are demo-units, is it still possible to de-brick them and register with Amazon?)
We can discuss price (by PM) after I get them and test them. The screens can be swapped between them. It has been reported here that after debricking, you can register with amazon and 3G works. My debricked K4 demo and K5 demo both registered successfully after debricking. You need to factory reset, because the built-in pre-registered demo accounts do not have 3G access.
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Old 10-11-2012, 04:24 AM   #11
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I tried again to see if I could revive it. I charged the battery (using a bench power supply, set to 4.1V, current-limited at 150mA) for about an hour last night. (I would have left it longer, but at the same time I didn't want to leave it over night.) It looked like the battery retained some charge, as the terminal voltage rose from 3.6V to 3.74V. However, this morning it was down to 3.55V (I left the battery in the kinde.)

My guess is that there's some short-circuit somewhere that drains the battery faster than the internal charging-circuitry can charge it. I have had a look at the accessible parts of the PCB, but I can't find any tin-whiskers, dust-motes or anything like that. I might try to flush it clean with compressed air and-or PCB cleaner, to see if that dislodges something. But if that fails I think I've got a broken PCB on my hands.

At the same time, I'm less and less inclined to spend much more time on it, as my Paperwhite should arrive in a couple of weeks.
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Old 10-11-2012, 05:32 AM   #12
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Hm, put a current meter in between battery and Kindle, just to see if it isn't the battery's internals that are de-charging? A counter-check for the theory that it's the Kindle draining it? But I do well understand that you're losing interest in the device when there's a KPW being shipped to you :-) Good luck in getting some money back on ebay for the trusty, old but unfortunately a bit broken K3. The display is fine, so it's still worth a bit.
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Old 10-11-2012, 05:38 AM   #13
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Hm, put a current meter in between battery and Kindle, just to see if it isn't the battery's internals that are de-charging? A counter-check for the theory that it's the Kindle draining it?
Yes, I wanted to do that, but at the time I couldn't come up with a neat way of connecting the cables to the battery. What I did instead was to attach my leads to the battery connector of the kindle. A bit ugly, I know, but it doesn't look like I've burned anything.

What Ill do next, instead, is to remove the battery and attach my power supply directly to the kindle. That way I can see (on my fancy power supply) how much current it's taking.


Can someone clarify that only the +/- terminals of the battery are used? I tried to connect a 'scope to the SDA/SDC terminals, but I never saw anything move.
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Old 10-11-2012, 08:03 AM   #14
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Old 10-11-2012, 08:35 AM   #15
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Question

I just played a bit more.

I connected my external power supply to the battery terminals (instead of the battery). The power supply is set to 4.1V (I've got some rather thin wires and I worry about the voltage drop. But measuring at the terminals it never dips below 3.9V.)

While the unit is 'idle' I measure a current draw of ~120mA. If I slide the power switch for 15 seconds the current draw drops to 0 until I release the switch, when it goes back to 120mA.

Sometimes¹ the current draw starts to fluctuate wildly between 80mA and 220mA. Sometimes the green LED starts flashing very slowly. (Five seconds on, five seconds off.)

During this entire procedure the screen didn't flicker a single pixel.

Unfortunately I don't have a PC close, so I can't say what it does on the USB.

¹I must admit that I'm not quite sure what caused this. I wasn't able to reproduce either phenomenon.
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