Stop Charging When Battery Reaches 100%

[jonlad1]

Is it possible to shut charging off when the battery reaches 100%?

I get scared when leaving it on charge overnight :blink:

 

[WizardStan]

The charging circuit is supposed to reduce the power going into the battery to exactly the amount that is being used by it. It's called a trickle charge. MWeston will be able to say for certain if this is working as it should. If it is, then it is doing what you want it to, and actually shutting off the charge may not be the best idea, at least not in the short term.

 

[mali]

There should be no problem leaving it plugged in.

[...]
The battery is always connected to the charger and will trickle charge once full (by design of the TI chip).

 

[jonlad1]

Ok fair enough, cheers guys

 

[mali]

(moved last posts to new topic http://www.gp32x.de/board/index.php?/topic/54733-charging-question/ )

 

[MWeston]

You could stop charging at 100% with some kernel work or maybe an app running in the background at all times. The problem is that when the charger is disabled, you would be back on battery power. So then you would want the app to maybe go back to charging when the battery fell to 90%. So while you sleep it would be going back and forth between 90 and 100%!

I've monitored the battery current drop down to about 16mA when fully charged and the cell voltage stops at about 4.18V I think (never actually gets to 4.20V for some reason but that's the PMIC hardware's job). That seems like a very nice light trickle charge current that should be safe enough for the hours you are not using the unit off the charger.

 

[jonlad1]

Awesome, cheers Michael

 

[WizardStan]

You could stop charging at 100% with some kernel work or maybe an app running in the background at all times. The problem is that when the charger is disabled, you would be back on battery power. So then you would want the app to maybe go back to charging when the battery fell to 90%. So while you sleep it would be going back and forth between 90 and 100%!

This seems like as good a thread to bump as any.
MWeston, I think I've found a bug/feature of the TI chip. Feature because that's how it is designed, bug because I disagree with the design choice.
There seems to be some fancy interactions going on in the charging chip. Sometimes it takes hours, sometimes only a few seconds, but sooner or later once it's reached 100% it trips the ICHGEOC flag and stops charging. I'm not entirely certain what the exact events that trigger the state are, all I know is that it is reasonably consistent. From what I understand of the state diagram, it's going from charge 2 to charge 3 to complete 1 to complete 3 to complete 2. It then sits in complete 2 until the voltage drops below 3.9V (level 2), about 85%, where it starts charging. This only happens when in "power save" mode, which would make sense since the diagram suggests it happens when the charge current drops below 80mA.

This would explain why some people (self included) have woken up to find their Pandora has stopped charging, perhaps even fallen several percent. From my experimentation (which involved leaving it plugged in for several hours and periodically checking the charge status registers) we would have found it started charging again at 85% if only we had left it that long. Instead it was assumed to be a problem and reported.

So I figured I'd post my findings, and ask if others would do the experiment of charging it to 100%, put it into standby, waiting for a few hours (it's taken me anywhere between 30 seconds and 4 hours, but the longer it has been charged the faster it triggers usually) and see if the charge light goes out. Then wait, leaving the charger plugged in, while it discharged to around 85% (though maybe give it until it reaches 80%) and see if it starts charging again.
If this is consistent with others as it is with me, then it should be noted this is not a bug or even a major problem as originally thought, it's a feature of the charging circuit which can be manipulated with software.

It does not explain the people who have found their battery to be almost dead the next morning. That's some very strange behavior I don't understand. But if the people with "normal" batteries can get the same behavior I have been, we should be able to figure out a way to "fix" it so it stays in trickle charge indefinitely.

edit: and it just happened while not in power save mode. So it can happen regardless of which mode it is, it just seems to be more likely when current usage is a lot lower.

 

[Yamara]

This would explain why some people (self included) have woken up to find their Pandora has stopped charging, perhaps even fallen several percent. From my experimentation (which involved leaving it plugged in for several hours and periodically checking the charge status registers) we would have found it started charging again at 85% if only we had left it that long. Instead it was assumed to be a problem and reported.

I've noticed the first steps of this behavior with my Pandora, but will have to watch it if begins to charge again at 85%. I'll keep an eye out. I just assumed it stopped charging entirely.

 

[sebt3]

Even so, there is something wrong : I plug mine late at night and I always get a full (as in 100%) battery in the morning.

 

[WizardStan]

Even so, there is something wrong : I plug mine late at night and I always get a full (as in 100%) battery in the morning.

Or is there something wrong with yours that it never reaches the "charge complete" state?

 

[sebt3]

Or is there something wrong with yours that it never reaches the "charge complete" state?

Maybe
What's the problems this could produce ?

 

[MichaelXX2]

You could overcharge the battery and start making it leak, and possibly explode. That poor Pandora will be killed in the explosion!

 

[WizardStan]

Maybe
What's the problems this could produce ?

Only thing I can think of is your Pandora is not dropping below the 80mA threshold, or maybe your battery has a slightly lower capacity than ours so the voltage never reaches the cutoff point (it's a very narrow limit), or maybe your charger has a slightly higher voltage than ours so is constantly trying to charge the battery to a level it will never reach. Like I said, all kinds of fancy and weird interactions seem to be going on in this thing.