On Sat, 14 Nov 2015 19:12:16 +0100 Pavel Machek <pavel@xxxxxx> wrote: > Hi! > > > > > Pavel Machek <pavel@xxxxxx> 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 <andreas@xxxxxxxxxxxx> > > > 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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