Re: [Gta04-owner] [PATCH 10/13] twl4030_charger: add software controlled linear charging mode.

[Andreas Kemnade]

On Sat, 14 Nov 2015 19:12:16 +0100
Pavel Machek  wrote:

> Hi!
> 
> > > > Pavel Machek  writes:
> > > > > On Thu 2015-07-30 10:11:24, NeilBrown wrote:
> > > > >> 
> > > > >> Add a 'continuous' option for usb charging which enables
> > > > >> the "linear" charging mode of the twl4030.
> > > > >> 
> > > > >> Linear charging does a good job with not-so-reliable power sources.
> > > > >> Auto mode does not work well as it switches off when voltage drops
> > > > >> momentarily.  Care must be taken not to over-charge.
> > > > >
> > > > > Can you explain how the user can "care not to over-charge"?
> > > > 
> > > > The following text reads:
> > > > 
> > > > It was used with a bike hub dynamo since a year or so. In that case
> > > > there are automatically charging stops when the cyclist needs a 
> > > > break.
> > > > 
> > > > so: take a break from cycling occasionally.
> > > 
> > > If the charger does not exceed 4.2V, I'd not call it overcharge. (Yes, 
> > > some clever
> > > chargers actually let the battery drop below 4.2V when charge is done, 
> > > but...)
> > > 
> > Yes, that is the case. Perhaps it is not to be called overcharge but
> > it is said that lithium battery charging has to stop if in CV mode the
> > current drops too low.  In automatic mode the charger does exactly
> > that.
> > I would not let a battery for days at 4.2V CV.mode although a lot
> > of cheap chargers
> 
> Well, I agree that keeping battery at 4.2V constant voltage mode is
> bad, but I'd not call it overcharge. If someone can fix the comment,
> that would be nice.
>
here is my original comment ("on" was replaced by continuous "now"):

twl4030_charger: add software controlled linear charging mode.

   adds a sysfs control node to achieve that.
   It can be set to
   auto: normal automatic charging is enabled (default)
   off: charging is off
   on: charing is on (software controlled)
   CC/CV mode is still automatically done,
   but end of charge due to low current not.

Note: If linear charging mode is used there should be some method of
stopping charging automatically. It is not a so time-critical, but
it is the wrong setting for leaving a charger connected for several
days since Lithium batteries should not be kept at 100% for longer
periods. Linear charging does a good job with not so reliable power
sources, since several voltage controlling is then often too
intelligent. It was used with a bike hub dynamo since a year or so. In
that case there are automatically charging stops when the cyclist needs
a break. Signed-off-by: Andreas Kemnade 


> > > If the charger _does_ exceed 4.2V, then the battery will explode. Don't 
> > > do that. Don't
> > > offer that to the user.
> > > 
> > > On a related note... I've just killed USB charger by overloading it. They 
> > > are not protected.
> > > 
> > > I believe your automatically-pull-max-power really should stick to the 
> > > well-known charging
> > > currents (.5A, 1A, 1.7A), at the very minimum.
> > > 
> > The main reason for the patch was to prevent switching off charging
> > when Vbus drops low. The reason was not to get out extremely much
> > current out of the charger.
> > The electrical characteristics of a  bicycle as a power source are.
> > - the amount of current available changes
> >- 500mA at around 17km/h
> > - you cannot destroy it by electrically overloading
> > 
> > If the current is set to e.g. 500mA and that linear charging mode is
> > enabled, the battery gets the maximum current available (upto
> > 500mA) regardless of the speed which is often changing.
> 
> Yes... I guess that makes sense for you, but I wonder if we should be
> doing this by default. It seems a lot of cheap chargers can be easily
> destroyed if you overload them.
> 
Hmm, I guess the twl4030_charger would not be the only one destroying
such chargers. I have seen such hub dynamo-friendly behaviour on every
device I had connected to it before (an ipaq h2200, openmoko gta02).
I have checked all usb wall plug chargers I have seen and I found none
which has a lower current then 500mA. Only one has 500mA. The rest has
1A or even 2A.

But I think the non-ending cv stuff is a reason enough so that it is not
the default charge method. I use it only at bootup when battery is low
to have some time to fix charging issues manually and when cycling.
Cycling is detected by acceleration values and I get some feedback if
that charge mode is enabled or disabled.

Regards.
Andreas Kemnade


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Re: [Gta04-owner] [PATCH 10/13] twl4030_charger: add software controlled linear charging mode.

[Pavel Machek]

Hi!

> > > Pavel Machek  writes:
> > > > On Thu 2015-07-30 10:11:24, NeilBrown wrote:
> > > >> 
> > > >> Add a 'continuous' option for usb charging which enables
> > > >> the "linear" charging mode of the twl4030.
> > > >> 
> > > >> Linear charging does a good job with not-so-reliable power sources.
> > > >> Auto mode does not work well as it switches off when voltage drops
> > > >> momentarily.  Care must be taken not to over-charge.
> > > >
> > > > Can you explain how the user can "care not to over-charge"?
> > > 
> > > The following text reads:
> > > 
> > > It was used with a bike hub dynamo since a year or so. In that case
> > > there are automatically charging stops when the cyclist needs a break.
> > > 
> > > so: take a break from cycling occasionally.
> > 
> > If the charger does not exceed 4.2V, I'd not call it overcharge. (Yes, some 
> > clever
> > chargers actually let the battery drop below 4.2V when charge is done, 
> > but...)
> > 
> Yes, that is the case. Perhaps it is not to be called overcharge but
> it is said that lithium battery charging has to stop if in CV mode the
> current drops too low.  In automatic mode the charger does exactly
> that.
> I would not let a battery for days at 4.2V CV.mode although a lot
> of cheap chargers

Well, I agree that keeping battery at 4.2V constant voltage mode is
bad, but I'd not call it overcharge. If someone can fix the comment,
that would be nice.

> > If the charger _does_ exceed 4.2V, then the battery will explode. Don't do 
> > that. Don't
> > offer that to the user.
> > 
> > On a related note... I've just killed USB charger by overloading it. They 
> > are not protected.
> > 
> > I believe your automatically-pull-max-power really should stick to the 
> > well-known charging
> > currents (.5A, 1A, 1.7A), at the very minimum.
> > 
> The main reason for the patch was to prevent switching off charging
> when Vbus drops low. The reason was not to get out extremely much
> current out of the charger.
> The electrical characteristics of a  bicycle as a power source are.
> - the amount of current available changes
>- 500mA at around 17km/h
> - you cannot destroy it by electrically overloading
> 
> If the current is set to e.g. 500mA and that linear charging mode is
> enabled, the battery gets the maximum current available (upto
> 500mA) regardless of the speed which is often changing.

Yes... I guess that makes sense for you, but I wonder if we should be
doing this by default. It seems a lot of cheap chargers can be easily
destroyed if you overload them.

Pavel
-- 
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(cesky, pictures) 
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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Re: [Gta04-owner] [PATCH 10/13] twl4030_charger: add software controlled linear charging mode.

[Andreas Kemnade]

On Tue, 6 Oct 2015 16:34:07 +0200
Pavel Machek  wrote:

> Hi!
> 
> > Pavel Machek  writes:
> > > On Thu 2015-07-30 10:11:24, NeilBrown wrote:
> > >> 
> > >> Add a 'continuous' option for usb charging which enables
> > >> the "linear" charging mode of the twl4030.
> > >> 
> > >> Linear charging does a good job with not-so-reliable power sources.
> > >> Auto mode does not work well as it switches off when voltage drops
> > >> momentarily.  Care must be taken not to over-charge.
> > >
> > > Can you explain how the user can "care not to over-charge"?
> > 
> > The following text reads:
> > 
> > It was used with a bike hub dynamo since a year or so. In that case
> > there are automatically charging stops when the cyclist needs a break.
> > 
> > so: take a break from cycling occasionally.
> 
> If the charger does not exceed 4.2V, I'd not call it overcharge. (Yes, some 
> clever
> chargers actually let the battery drop below 4.2V when charge is done, but...)
> 
Yes, that is the case. Perhaps it is not to be called overcharge but
it is said that lithium battery charging has to stop if in CV mode the
current drops too low.  In automatic mode the charger does exactly
that.
I would not let a battery for days at 4.2V CV.mode although a lot
of cheap chargers 

> If the charger _does_ exceed 4.2V, then the battery will explode. Don't do 
> that. Don't
> offer that to the user.
> 
> On a related note... I've just killed USB charger by overloading it. They are 
> not protected.
> 
> I believe your automatically-pull-max-power really should stick to the 
> well-known charging
> currents (.5A, 1A, 1.7A), at the very minimum.
> 
The main reason for the patch was to prevent switching off charging
when Vbus drops low. The reason was not to get out extremely much
current out of the charger.
The electrical characteristics of a  bicycle as a power source are.
- the amount of current available changes
   - 500mA at around 17km/h
- you cannot destroy it by electrically overloading

If the current is set to e.g. 500mA and that linear charging mode is
enabled, the battery gets the maximum current available (upto
500mA) regardless of the speed which is often changing.

Regards,
Andreas Kemnade


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Re: [Gta04-owner] [PATCH 10/13] twl4030_charger: add software controlled linear charging mode.

[Christ van Willegen]

Hi all,

On Tue, Sep 15, 2015 at 1:28 PM, Pavel Machek  wrote:
> On Thu 2015-07-30 10:11:24, NeilBrown wrote:
>>
>> Add a 'continuous' option for usb charging which enables
>> the "linear" charging mode of the twl4030.
>>
>> Linear charging does a good job with not-so-reliable power sources.
>> Auto mode does not work well as it switches off when voltage drops
>> momentarily.  Care must be taken not to over-charge.
>
> Can you explain how the user can "care not to over-charge"?

Just my $0.02, I assumed (whoops!) that Neil mean that the _code_
should take care not to over-charge... but not sure how he intended to
to that.

Anyway, that was my interpretation of the (indeed, it could be
explained in different ways...) comment.

Christ van Willegen
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