| joerg | I'd guess it's chemophysically impossible to charge a LiIon cell to 4.7V | 03:31 |
|---|---|---|
| joerg | and it's absolutely impossible that the PROT circuitry doesn't cut out charging before the cell reaches that voltage, even if the cell _could_ reach that voltage | 03:32 |
| L29Ah | it isn't | 10:40 |
| L29Ah | i already did that, but the cell vented | 10:40 |
| L29Ah | after i reset the pressure relief valve, the cell read 4.9V | 10:41 |
| L29Ah | now, back to N900, i plugged N900 off the charger, then opened the cover and unplugged the battery, then measured 4.7V on it with a multimeter | 10:42 |
| L29Ah | plugged it back, power-cycled N900, unplugged it, measured 4.45V | 10:43 |
| System_Error | Looks like blatant overcharge to me. | 10:43 |
| L29Ah | so the circuitry is out or nonexistant | 10:43 |
| L29Ah | the battery is from aliexpress so might be they saved on inessential components ;) | 10:43 |
| L29Ah | still i wonder how that happened from N900's PoV: does it expect the intact circuitry, or my software is faulty, or my hardware is faulty, or something? | 10:44 |
| KotCzarny | cue the ~~livin' on the edge~~ theme | 11:10 |
| Maxdamantus | Do you ever use OTG mode? looking at the datasheet for bq24150a (that's the chip in N900, right? need to get mine out of my bag), I get the impression that it's not going to prevent the battery voltage from reaching that level. | 12:12 |
| Maxdamantus | not going to prevent it in boost mode, that is. | 12:13 |
| Maxdamantus | (though I'm not particularly familiar with reading these sorts of datasheets) | 12:13 |
| Maxdamantus | Hm, yeah, it says it only turns off the PWM converter when the battery is at 4.75 V in boost mode. | 12:22 |
| Maxdamantus | I think I remember something getting stuck in some mode when using OTG. If that included the bq chip being left in boost mode, I imagine there wouldn't be anything to stop power being backfed up to 4.75 V next time it's plugged into USB, since the bq chip will just think that it's boosting that battery voltage up to the VBUS voltage (USB). | 12:34 |
| L29Ah | i don't, but may have experimented with it in the past | 14:27 |
| joerg | you killed your DMM or your N900. The circuitry in N900 as well as the circuitry in a legit Nokia BL-5J battery forbids charging to anything >4.3V | 19:25 |
| joerg | 4.45V sounds like about absolute physical limit to which you can pump up a LiIon chemistry that didn't already turn into a chemical waste dump | 19:30 |
| joerg | at that voltage is is about to turn into said waste dump | 19:30 |
| joerg | after sufficient torturing you can turn a LiIon cell into something you may "charge" to dozens of Volts, alas with a capacity of maybe 0.1mAh | 19:32 |
| joerg | iirc ABSMAX voltage on battery pins of the N900 charger circuitry is sth around 5V, above which you will fry the circuit | 19:33 |
| joerg | so even the 0.1mAh of such wreck in schape of a LiIon could kill your N900 wen you remove it from a totally fubar external charger and insert it to N900 | 19:34 |
| joerg | http://neo900.org/stuff/block-diagrams/neo900/neo900.html "Batt charger -> N900 LEGACY -> Data sheet" http://www.ti.com/lit/ds/symlink/bq24150a.pdf sorry I was a tad wrong, it's 7V actually >>ABSOLUTE MAXIMUM RATINGS VI Input voltage range (with respect to and PGND) SCL, SDA, OTG, CSIN, CSOUT, AUXPWR –0.3 to 7 V [ Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device]<< So the statement above still | 19:42 |
| joerg | applies 100% | 19:42 |
| joerg | and no, you can't make the N900 charge battery to 4.9V, see >> V(OREG) Output charge voltage Operating in voltage regulation, programmable 3.5 ~ 4.44 V<< | 19:47 |
| joerg | actually VBUS (5V) is a natural limit for how high you *theoretically* could charge the battery in N900 since the BQ24150 only has a buck converter for charging that can not boost voltage | 19:52 |
| joerg | however a terribly fried buck converter might actually feed through the input voltage (5V VBUS) to output unregulated | 19:54 |
| Maxdamantus | 07:52:46 < joerg> actually VBUS (5V) is a natural limit for how high you *theoretically* could charge the battery in N900 since the BQ24150 only has a buck converter for charging that can not boost voltage | 21:20 |
| Maxdamantus | So what does the "boost" mode do then, and why does the datasheet say that it can boost the voltage? | 21:20 |
| Maxdamantus | 22 minutes till my N900 is charged. will see what happens if I enable boost mode afterwards. | 21:33 |
| Maxdamantus | interestingly, if I enable boost mode while it's connected to a charger (dumb power source with D+/D- shorted), the reported battery is lower than if it's off charge and it looks like it's draining faster. | 21:45 |
| Maxdamantus | maybe that just means that it's boosting to a voltage higher than the charger. | 21:45 |
| Maxdamantus | reported battery voltage* | 21:45 |
| Maxdamantus | Yeah, the datasheet says that it will bost to 5.05. I think I've measured the open circuit voltage of the charger I'm using at just under 5 V. | 22:00 |
| Maxdamantus | If I connect my charger in parallel to some lead-acid batteries and disconnect AC (it's one of those "universal chargers", and it's able to backfeed in any direction), the N900 discharges at a lower rate. | 22:03 |
| Maxdamantus | but I'm guessing if the charger maintained over 5.05 V, the bq24150a chip would probably allow current to backflow in boost mode. | 22:04 |
| Maxdamantus | Maybe I should get an actual bench power supply sometime so I can actually experiment with things like this. | 22:08 |
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