From holt at laptop.org Tue Mar 26 18:57:05 2019 From: holt at laptop.org (Adam Holt) Date: Tue, 26 Mar 2019 15:57:05 -0700 Subject: [Power] Fwd: Charging XO-1 batteries having extreme cell imbalance In-Reply-To: <616661146.321980.1553640719468@email.ionos.com> References: <616661146.321980.1553640719468@email.ionos.com> Message-ID: From: Date: Tue, Mar 26, 2019, 3:52 PM Subject: [support-gang] Charging XO-1 batteries having extreme cell imbalance To: Charging XO-1 batteries having extreme cell imbalance. Here is our procedure for charging batteries with very short run times (minutes) followed with very short charge times (minutes). Tested on series 4 and series 8 batteries. On information, some series 1 batteries may not have cell balancing circuits. Comments welcome. Some laptops received for repair have batteries that will not power the laptop for more than a few minutes or, in some cases, not at all. These fall into three groups: infinite trickle charge, green battery LED but will not power XO-1 or charge, or battery run times of minutes followed by short charging time. In the past, all required drilling pin holes in the plastic case and testing the individual cells and, where cells were not open or shorted, charging from external sources. Using “bat-recover” in the newer firmware, the batteries in the last group would start to charge and when the voltage reached 7.500 volts, the charging current would go to 0.0 mA. After, several minutes, the charging would start again and the charge / nocharge cycle repeated continuously with very little accumulation of charge. Hence, the batteries were perceived as not restorable unless an invasive procedure was used. Recently, it was discovered that if the charging power was interrupt 5 seconds every 60 seconds, the charge would accumulate much faster. After the accumulation of 200 - 500 mAh, charging was continuous, as normal. One battery falling into this group would not power the XO-1, but did show some charging time. When the charging power was interrupted while running bat-recover, the XO-1 would shut down. The cycle of power XO-1, start bat-recover, and interrupt charging power was repeated until about 50 mAh had accumulated, where the XO-1 remained powered when the charging power was interrupted. The working procedure is to accumulate, using bat-recover, sufficient battery charge to keep the XO-1 running when the charging power in interrupted. Then, interrupt the charging power for 5 to 10 seconds after the charging current drops to 0.0 . When the charging current ceases the periodic dropping, continue bat-recover until the battery is fully charged. Interruptions of more about 10 seconds does not seem to increase accumulation rate. To minimize residual imbalance, use bat-recover (no AC power) to charge the battery (AC power) to about 15% (500 mAh). Power off, power (no AC power) on again and let the XO-1 run normally until it shuts down with the red battery LED. Use bat-recover to fully charge the battery again. Expect the full accumulated charge to range between 2700 - 2900 mAh. New battery spec is 2800 mAh. Values near 3000 may be observed if the battery is completely discharged with bat-recover, but only the 2800 will be available in OLPC use. A developer key is needed to access the firmware / bat-recover on the XO-1. Key is not needed with the XO-1.5 . It appears that the linearity in the current - voltage curve in partially discharged cells and the non-linearity near full charge makes this procedure possible. Furthermore, it is postulated that slower charging rates allow the cell balancing circuit in the battery to accumulate greater balancing charge. N.R. Michigan XO Laptop Community Repair Center xoapart at xoshare.org http://xoshare.org -------------- next part -------------- An HTML attachment was scrubbed... URL: From quozl at laptop.org Tue Mar 26 19:18:10 2019 From: quozl at laptop.org (James Cameron) Date: Wed, 27 Mar 2019 10:18:10 +1100 Subject: [Power] Fwd: Charging XO-1 batteries having extreme cell imbalance In-Reply-To: References: <616661146.321980.1553640719468@email.ionos.com> Message-ID: <20190326231810.GC13742@laptop.org> Yes, that's a workable procedure. Also the operation of the cell balancing circuit releases heat in the vicinity of the switching MOSFET on the PCB in the battery. So with careful monitoring of the nearby temperature sensor a few millimetres away, or a thermal probe, you can deduce when the cell balancing circuit is working hard. A technician may also provide external charging current to the pins on the battery. The battery protection circuit shall operate to prevent overcharge or fire. But this won't update the capacity estimate stored by the battery. During one test, I used an Arduino Uno to communicate with the battery chip. It is relatively straightforward, using public datasheets. -- James Cameron http://quozl.netrek.org/