Date: Fri, 20 Jan 2017 18:18:16 -0500 From: Jon Radel <jon@radel.com> To: freebsd-questions@freebsd.org Subject: Re: stop charging laptop battery when full Message-ID: <dd1c5f53-ca95-5c2f-1818-3322576c2892@radel.com> In-Reply-To: <20170120200826.GA2070@c720-r292778-amd64> References: <20170120171125.GA3965@c720-r292778-amd64> <20170120135008.5168cc79@riseup.net> <20170120200826.GA2070@c720-r292778-amd64>
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This is a cryptographically signed message in MIME format. --------------ms050602030803080000060901 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 1/20/17 3:08 PM, Matthias Apitz wrote: > El d=C3=ADa Friday, January 20, 2017 a las 01:53:50PM -0500, Sergei Akh= matdinov escribi=C3=B3: >=20 >> On Fri, 20 Jan 2017 18:11:25 +0100 >> Matthias Apitz <guru@unixarea.de> wrote: >>> I can ask the current capacity (and other values) of the battery with= : >>> [snip] >>> While charging, is there a way to stop the charging when >>> hw.acpi.battery.life reached 100 to protect the (LI-ion) battery? >> >> Such functionality should be provided by your battery's internal circu= itry. >> Think about it, it wouldn't be safe for any consumer to buy a laptop w= hich >> doesn't switch to DC power when the battery is full. >=20 > I'm not sure about this. Let's assume the power provided by the charger= > it withdrawn "somehow" from the battery and the laptop runs only on the= power > provided by the charger. The battery will now start to drain itself (du= e to > its internal resistor value). When it will start to charge again, and > how? The somehow would be the rather sophisticated charging circuit found in any recent laptop that was properly designed. Yes, the battery will slowly drain. It will start to charge again when it hits whatever threshold the charging circuit considers appropriate, which hopefully is enough below the threshold used to stop charging to provide enough hysteresis to avoid thrashing too much. All of those values chosen by engineers beaten about the head by marketing types who want to claim maximal battery life, and management types who want to make sure the battery lasts through at least the warranty period. True, vaguely related story: I was nearly driven crazy one night by my iPhone plugged into an external battery pack right beside my bed. The "I've been plugged into power" noise is one of the few that is not suppressed by the Do Not Disturb feature. So I went to sleep while it was happily charging. When the phone was fully charged, it stopped charging and the current draw dropped below the battery pack's threshold for "I'm not really being used and supplying a trickle will drain my battery, so I'll mostly shut off output." At that point the phone, convinced it was no longer plugged into power, ran on its battery until it dropped below the appropriate threshold and started charging again, at which point the external pack turned on output again and the phone bleedled in my ear. That kept going all night, never waking me up quite enough to deal with it...I pieced it together the next morning. >=20 > And why all the hints say: Once fully charged, disconnect the laptop > from charger? I sincerely doubt that all the hints say this, merely a great number of them. Reasons for this I can think of include: 1) Hints from people who don't understand how sophisticated charging circuits have become, and 2) Hints from people who don't realize that Ni-Cad and Li-Ion batteries are very, very different, and 3) Hints from people who understand what the charging tradeoffs are and wish to do something different that what the engineers of the charging circuit ended up doing, and 4) Hints from people who are generalizing the need to fully discharge periodically on some devices if you wish to re-calibrate the battery monitoring. In many cases I suspect it's hard to tell where the advice is coming from. Good luck sorting them out. >=20 > Will it lead to some endless charge/discharge cycle? More or less. But why the concern? >=20 > I was asking for some method to disconnect the laptop completely from > the charger, either internally or, for example, by some external device= , > receiving the signal via Wifi and cutting the charger from the outlet. I suspect that that would be a fun project for a Raspberry Pi hooked up to a relay. Actually, if you're going to go to that extent, you might want to first have a good go at analyzing the current/voltage across your charging cable, which would go far in determining what is really happening with your laptop's charging--much more likely to be accurate than speculation by random people like me on this list. :-) BTW, the more often, and the deeper you discharge your Li-Ion battery, the sooner it will wear out. So disconnecting the charger every time you hit full charge and then discharging the battery most or all the way will shorten the battery's life. See http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_b= atteries for some actual numbers, followed by much argumentation in the comments as to what it all really means. Now, what would be really cool would be to build your little Raspberry Pi & relay box to disconnect the charger at a lower than maximum voltage so as to maximize battery lifetime, rather than maximizing the runtime of a "full" charge. See above referenced article for more. --=20 --Jon Radel jon@radel.com --------------ms050602030803080000060901 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCC Cq8wggSvMIIDl6ADAgECAhEA4CPLFRKDU4mtYW56VGdrITANBgkqhkiG9w0BAQsFADBvMQsw CQYDVQQGEwJTRTEUMBIGA1UEChMLQWRkVHJ1c3QgQUIxJjAkBgNVBAsTHUFkZFRydXN0IEV4 dGVybmFsIFRUUCBOZXR3b3JrMSIwIAYDVQQDExlBZGRUcnVzdCBFeHRlcm5hbCBDQSBSb290 MB4XDTE0MTIyMjAwMDAwMFoXDTIwMDUzMDEwNDgzOFowgZsxCzAJBgNVBAYTAkdCMRswGQYD VQQIExJHcmVhdGVyIE1hbmNoZXN0ZXIxEDAOBgNVBAcTB1NhbGZvcmQxGjAYBgNVBAoTEUNP TU9ETyBDQSBMaW1pdGVkMUEwPwYDVQQDEzhDT01PRE8gU0hBLTI1NiBDbGllbnQgQXV0aGVu dGljYXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCC AQoCggEBAImxDdp6UxlOcFIdvFamBia3uEngludRq/HwWhNJFaO0jBtgvHpRQqd5jKQi3xdh 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