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[Q] batery usage 24*7

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nitu12345
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Cool [Q] batery usage 24*7

I am new to this forum
Just wanna ask if i switch on my nexus7 wifi 24*7 then will it affect its wifi??
Just curious to know becoz i rarely switch off my wifi and i am scared will itt damage it after sometime??
 
bftb0
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Heat accelerates almost all aging & failure mechanisms.

Temperature cycling accelerates some types of failure mechanisms (fracture/rupture type failures)

So leave it on or turn it off every night, which is worse?

So long as you aren't streaming data at full bore 24x7 you will probably be fine leaving it on.

Note I said *probably*. That's because I certainly do not have accelerated life-test data for the N7 sitting in front of me; but even if I did, those statistics would only predict what fraction of units would fail over yeah-many hours/years of service... not which individual units will fail.

So unless someone from Asus comes in here and divulges what their MTBF design goal for the N7 was, or what the first 18 months of the repair stream has indicated about their reliability models, you're not going to get much of an answer to your inquiry.

FWIW, I leave mine on the charger & with the WiFi on when I am not using it, and I have the expectation of using it for a couple more years to come.
"I'm gonna start coding placebo apps. That way I will be sure that the complaints are real and the praises hollow."
 
nitu12345
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Quote:
Originally Posted by bftb0 View Post
Heat accelerates almost all aging & failure mechanisms.

Temperature cycling accelerates some types of failure mechanisms (fracture/rupture type failures)

So leave it on or turn it off every night, which is worse?

So long as you aren't streaming data at full bore 24x7 you will probably be fine leaving it on.

Note I said *probably*. That's because I certainly do not have accelerated life-test data for the N7 sitting in front of me; but even if I did, those statistics would only predict what fraction of units would fail over yeah-many hours/years of service... not which individual units will fail.

So unless someone from Asus comes in here and divulges what their MTBF design goal for the N7 was, or what the first 18 months of the repair stream has indicated about their reliability models, you're not going to get much of an answer to your inquiry.

FWIW, I leave mine on the charger & with the WiFi on when I am not using it, and I have the expectation of using it for a couple more years to come.
recently i played hd movie on my nexus 7
(Movie-300 blue ray version
Frame width-1280
Frame height- 544
frame rate - 23 frames per sec )


and found playback time of 5hrs only
I didn't played entire movie jst calculated in the form that my battery level reduced from 93 to 92 in exact 3 min
Like this i calculate entire playback time ,....
But on internet it says nexus 7 support 9 hrs of hd playback
Plz tell 5 hrs playback is fine for bluray version or I'm having some sought of a battery issue
And if it's a battery issue then what shall i do for its replacement because its been only 1 months
Plz do reply asap.

Regards.
 
bftb0
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Quote:
Originally Posted by nitu12345 View Post
recently i played hd movie on my nexus 7
(Movie-300 blue ray version
Frame width-1280
Frame height- 544
frame rate - 23 frames per sec )


and found playback time of 5hrs only
I didn't played entire movie jst calculated in the form that my battery level reduced from 93 to 92 in exact 3 min
Like this i calculate entire playback time ,....
But on internet it says nexus 7 support 9 hrs of hd playback
Plz tell 5 hrs playback is fine for bluray version or I'm having some sought of a battery issue
And if it's a battery issue then what shall i do for its replacement because its been only 1 months
Plz do reply asap.

Regards.
Three minutes (or a 1% change) in battery "percent charge state" is way way too small of an interval to extrapolate from - the sampled data is just way too noisy to be meaningful. A 10% change would be a better measurement. And, those types of measurements should be made in the "middle" of the battery charge state (in the 30% - 70% range, not near the ends).

But - to answer your question - quite a long time ago, @bcvictory ran many battery drain tests - using a video loop test - with a bunch of different kernels, and most of the results tended to be between 5 and 7 hours or so.

I made some very detailed battery drain measurements playing a video loop about 4 weeks ago on my N7 (MX Player), and without tweaking anything (stock kernel, KitKat 4.4.2) I got about 6.25 hrs for a full discharge (100% - 4%).

So, I guess that means that if you saw an Asus/Google claim of 9 hours, that would probably be a significant exaggeration.

(BTW, keep in mind that for *movies* the GPU isn't doing all that much work, as the scenes are not being rendered from a model - they are just being decompressed from a file (or byte stream). So... that means that you should probably expect even worse battery drain times for playing video games continuously).

.
"I'm gonna start coding placebo apps. That way I will be sure that the complaints are real and the praises hollow."
 
nitu12345
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Default nexus 7 overcharging

Quote:
Originally Posted by bftb0 View Post
Three minutes (or a 1% change) in battery "percent charge state" is way way too small of an interval to extrapolate from - the sampled data is just way too noisy to be meaningful. A 10% change would be a better measurement. And, those types of measurements should be made in the "middle" of the battery charge state (in the 30% - 70% range, not near the ends).

But - to answer your question - quite a long time ago, @bcvictory ran many battery drain tests - using a video loop test - with a bunch of different kernels, and most of the results tended to be between 5 and 7 hours or so.

I made some very detailed battery drain measurements playing a video loop about 4 weeks ago on my N7 (MX Player), and without tweaking anything (stock kernel, KitKat 4.4.2) I got about 6.25 hrs for a full discharge (100% - 4%).

So, I guess that means that if you saw an Asus/Google claim of 9 hours, that would probably be a significant exaggeration.

(BTW, keep in mind that for *movies* the GPU isn't doing all that much work, as the scenes are not being rendered from a model - they are just being decompressed from a file (or byte stream). So... that means that you should probably expect even worse battery drain times for playing video games continuously).

.
Sir by mistake i overcharged nexus7 tablet for 1 hour and found out that
That it didn't get discharged for next 1 hour ( in which i surf web , watch youtube videos,and played temple run )
Don't you think it get overcharged for i hour because last time i removed the charger at exact 100 % and it started draining within that i hour

And plz do tell even if tablet gets overcharged
Is it safe ?
Becoz i usually charge my tablet at night.
 
bftb0
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(Last edited by bftb0; 29th January 2014 at 05:45 AM.)
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Quote:
Originally Posted by nitu12345 View Post
Sir by mistake i overcharged nexus7 tablet for 1 hour and found out that
That it didn't get discharged for next 1 hour ( in which i surf web , watch youtube videos,and played temple run )
Don't you think it get overcharged for i hour because last time i removed the charger at exact 100 % and it started draining within that i hour

And plz do tell even if tablet gets overcharged
Is it safe ?
Becoz i usually charge my tablet at night.

I wrote a script to "watch" the battery current and voltage in my N7 once per minute (while it was charging from about 4% - 100%) and log the output to a file. (see attached image). So, I think I know exactly why you saw the results you did.

So here is what happens: as the battery voltage rises during charging, the current slowly gets smaller and smaller. Somewhere around 90% the current suddenly starts to slow down much faster in time, and the battery voltage only rises a tiny bit over the 90% - 100% interval.

Here was the surprise though: when the "% charge" got to 100%, the battery continued to charge (slowly) for another 20 minutes. Over that 20 minutes the battery charging current eventually went to zero.

So - it is safe to let your tablet sit on the charger. It is not the charger that determines how much current the battery receives, it is the SMB347 chip in the N7. There is no such thing as "overcharging" so long as the hardware in the tablet is operating correctly. I leave my tablet on the charger all the time when I am not using it, and don't worry about that one bit.
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"I'm gonna start coding placebo apps. That way I will be sure that the complaints are real and the praises hollow."
The Following User Says Thank You to bftb0 For This Useful Post: [ Click to Expand ]
 
nitu12345
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Quote:
Originally Posted by bftb0 View Post
I wrote a script to "watch" the battery current and voltage in my N7 once per minute (while it was charging from about 4% - 100%) and log the output to a file. (see attached image). So, I think I know exactly why you saw the results you did.

So here is what happens: as the battery voltage rises during charging, the current slowly gets smaller and smaller. Somewhere around 90% the current suddenly starts to slow down much faster in time, and the battery voltage only rises a tiny bit over the 90% - 100% interval.

Here was the surprise though: when the "% charge" got to 100%, the battery continued to charge (slowly) for another 20 minutes. Over that 20 minutes the battery charging current eventually went to zero.

So - it is safe to let your tablet sit on the charger. It is not the charger that determines how much current the battery receives, it is the SMB347 chip in the N7. There is no such thing as "overcharging" so long as the hardware in the tablet is operating correctly. I leave my tablet on the charger all the time when I am not using it, and don't worry about that one bit.
That means my battery's working fine..na??
Can u suggest me a gud free app to scan battery's performance?
Hws BetterBatteryStats_xdaedition_1.15.0.0 ?

And thanks a lot for clearing my doubts
U r bst
 
bftb0
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Default What does "Battery Charge %" Mean?

Quote:
Originally Posted by nitu12345 View Post
That means my battery's working fine..na??
Can u suggest me a gud free app to scan battery's performance?
Hws BetterBatteryStats_xdaedition_1.15.0.0 ?

And thanks a lot for clearing my doubts
U r bst
@nitu12345 - I don't use battery monitoring apps. I'm not really sure what value they have except in deciding whether or not your battery is sort of "normal". Some of them try to "estimate" current rather than actually take measurements from hardware (which depends on the availability of both system hardware and kernel software, so it makes sense why a generic Android battery app might not even look at current measurements even when they are available on a particular handset/tablet) , so: garbage-in = garbage-out. Basically though, I can't make a recommendation as I haven't used them.


TL;DR - see attached plots at end of post.

I want to take this opportunity to show some more data that I measured in the hopes that it can add to folk's understanding. I made a bunch of measurements of my tablet under both discharge and charging conditions, Originally I was going to make a big long post, but it was simply too much effort to do a good job of it with all the data I had. So here is a mini-report about charging. In particular, it asks and answers the question:


"What exactly does charge percentage mean"?

Is it the measurement of Amp-hours pumped into the battery?
Or is it somehow proportional to battery voltage?
Something else?

Before I begin I should point out just a few key observations. The 2012 N7 has a TI (Texas Instruments) chip - the BQ27541 (iirc), that has the sole purpose of observing the battery - the amount of current going into or out of the battery, and the battery voltage. It does NOT CONTROL ANYTHING - it is just an observer. For that reason, TI calls it a "fuel gauge" chip. It is connected to the processor via an I^2C bus, and the N7's kernel reads the "% charge" directly from this chip. There is no system "battery software" or "calibration software" which alters this number in the N7 - it comes directly from that BQ27541 chip. No doubt there is a tiny amount of firmware in that chip, and the datasheet for that chip indicates it can be factory programmed with different battery curves. But for our purposes it is a black box that we can't easily change - the kernel interface on the N7 does none of that "factory programming", it just reads values from the "black box".

From that chip several things can be read - "% charge", "battery current", "voltage", etc.

Attached at the bottom of this post you will find a curious graph. It shows the behavior of five measurements versus time. "Potential", "Charge", "Current", "Energy", and "Percent". The reason that I said "curious" is that all the raw data were re-scaled so that the min-to-max range of each variable are "normalized" to the range 0.0 to 1.0 (except for the "Percent" variable, since charging here started at 6%).

for any given variable this is done by subtracting the minimum value from the dataset, and then dividing by (max - min), as in:

x' = [ x - min(x) ] / [ max(x) - min(x) ]

Why do things this way? Well, for one, so that all the different variables may be plotted on a single graph running from 0.0 to 1.0.

But more importantly, observing the "shape" of each curve in comparison to others gives you very good physical insight into what is happening under the hood.


A little background in physics:

I Current == Charge/second
Q Charge == Integrate[Current(t), dt] (note this is effectively the same thing as "Amp-hours")
P Power == Voltage*Current
E Energy == Integrate[Power(t), dt]
V Potential (= Battery Voltage)

So from measurements of I(t) and V(t) only - current and voltage, we can use numerical integration to figure out approximate values of Q (charge), and E (energy, or "work" that we put into the battery), starting from only the I(t) and V(t) measurements.



So finally - look at the first JPG image carefully. ("nexus7-2012-Normalized_ChargeCurrentVoltageEnergyPct_vs_Time.j pg")

What you will notice is that three variables: Charge (Q), Energy (E), and Percent all rise quite smoothly in a nearly straight line from 6% to 90% charge state, (or from 0 secs to 9000 secs). So this says that - even though the battery voltage is not smoothly increasing, nor is the current into the battery smoothly decreasing - the charging discipline enforced by the other important chip in the N7 (the SMB347 USB Interface Chip) tries to perform a "constant power input" charging scheme.

A quick diversion: why is the shape of the Energy (E) curve almost identical to the Charge (Q) (or Amp-Hours) curve? It is because of the (apparent) "constant power input" scheme the charger uses: as the battery voltage rises, the amount of current used for charging is adjusted downward. Notice in the graph that even though the "Percent" variable is steadily rising in a straight line, neither the current nor voltage are behaving that way - they are almost inverses of each other so that I(t) * V(t) = Constant.

So - the conclusion, specifically for the N7 hardware - is that "battery percentage" is supposed to represent either Amp-hours input to the battery (charge), or Energy dumped into the battery during charging. For this specific device with it's specific hardware, they happen to be equivalent because of the constant power charging scheme.

Note there are a couple of other interesting tidbits in this graph. The charging cycle spends nearly 25% of the total time charging in the final 90-100% charging range. So if you are carefully watching your tablet charge, it will seem to "slow down" dramatically during that last 10% of charging. (I should also point out that my tablet charges quite a bit faster under normal circumstances - about 2.5 hours instead of 3.5 hours; I believe the script I used prevented the tablet from ever entering deep sleep during charging. A N7 tablet that isn't being held awake with wakelocks should charge in a little over 2.5 hours)

You will also notice that the battery is continuing to charge for about 20 minutes after it reached the "100%" charge state. That's because "100%" doesn't really mean that the battery has stopped charging. In this particular observation, the SMB347 chip was still pushing ~400 mA into the battery after the 100% mark had been reached.

Phew. Finally, I have attached another image ("nexus7-2012-BatteryVoltage_vs_ChargePct.jpg") that shows a display of battery voltage versus percentage charge for two charging cycles and one discharge cycle. Note that when the SMB chip needs to force current into the battery to charge it, it must raise the voltage in order to do that. So it is clear that battery voltage alone can not be used as a proxy for "charge percent", nor can you figure out what the charge is by only looking at battery voltage alone. Not only that, but look at the shape of the curve - it is not a straight line. There is very rapid voltage changes going on at the low end of "% charged" range during charging, very little voltage change occurring in the 90-100% range, and during discharge (red curve) there are are at least 3 different ranges where the slope of the battery voltages change relative to the "% charge" data that the TI chip emits. This is why I suspect that battery apps that only observe voltages probably are not capable of accurately predicting anything other than the ageing algorithms of the BQ27541 chip, and are probably absolutely useless for telling you anything from day to day.

OK, a couple more trivia observations:

- That BQ27541 chip is squirrelly (or perhaps it is the kernel interface, dunno.) There were many sampled data points where the "% charge" reading from the chip suddenly dropped from wherever it had been to *ZERO*. I was sampling the value once every 60 seconds for the data displayed here, but I have also sampled the sysfs (kernel interface) for that chip at much higher speeds, and it frequently produces garbage data. Additionally, the same chip would frequently report *zero current* during discharge condtion - an impossibility. On their website, TI says "Not recommended for new designs". (Usually that is weasel-words that mean "we are aware of some buggy behavior that we are not going to tell you about") Note for instance in the second graph that the battery percentage values 26, 47, 58, 69, 79, and 84% never appear in ANY data set. That means that a battery app - or even an OS "low battery emergency shutdown" trap - could exhibit odd, buggy behavior if they do not use defensive techniques that assume that the data they are getting is partly corrupted. (multiple sample averaging and outlier detection).

- I believe the "sudden steps" in current that I observed during charging (prior post) were real - the tablet had it's WiFi shut off, and the tablet was not in use at all. So while it is certainly possible that random app behavior could have caused some fluctuation in current available to the battery, that would have been much more short lived. Is it possible that the SMB347 chip also has some bugs?

OK, here's the graphs folks. Have fun and good luck with your tablet.

bftb0
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"I'm gonna start coding placebo apps. That way I will be sure that the complaints are real and the praises hollow."
 
nitu12345
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Recently i reseted my nexus tablet and found that there was no google earth installed so I downloaded an apk file frm external source and installed google earth from it
but now when i try to uninstall it
There no such button as it shows only disable button
But since it wasn't there before how come now its not uninstalling

N r u using magnetic case .? Is it safe for nexus7?
Like i have heard that it messes with magnetic compass

Plz clear my query.

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