The 15% level.... please help me understand something that's been bugging me for a little while.
It makes perfect sense that the only way to correctly set the 100% flag is to charge with the device powered off. I understand the possibility of a deep discharge -- that is, zero could be less than zero, but how can it accurately set the 15% flag (or 5% flag) if it doesn't know where zero is? In other words, could 15% really represent 25% (or 5%) as time goes on? Logically, it seems to me that it would need to know both values (100% and 0%) to correctly set any intermediate warnings. It seems like a catch 22 situation.... you don't want to drain it completely but there's no ideal way to accurately set the low level flags. Am I way off base or is this like picking fly crap out of pepper?
Ready to start my Master's at FoxKat U.
that is a good question. if you never let it hit zero how oes your battery know that 0 represents 0. if you charge constantly from 15% wouldnt your battery believe 0 is 15% thsmus losing that 15 percent of space in the battery. and over time your phone loses that 15% and thinks 15 is 0. then after a while loses 15% more. and so on. in time really weakening the batrery? i may not understand this correctly but as of right now that is what it sounds like to me. it really seems like nobidy is 100% on how to really mantain a healthy battery because there are all sorts of "theories". forgive me if im completely missing the point. im far from a battery expert.
Sent from my BLACK DROID RAZR using Droid Forums. Prepare to be impressified!!!!
also forgive my grammar. evidently my keyboard cant keep up with what i was typing lol. time to switch back to stock.
Sent from my BLACK DROID RAZR using Droid Forums. Prepare to be impressified!!!!
OK gentlemen, a great question and there's a relatively simple answer.
This particular battery chemistry has a unique quality that bodes well for devices like ours. It provides relatively steady power at a range of voltages that is only a few tens of percentage points per hour of discharge from about 80% charge level all the way down to about 20% charge level. This is both good and bad. Electronics NORMALLY perform at different capacities depending on the voltages applied, however in computers they are designed to operate at the same level of performance across a relatively narrow range of voltages. Anything less is boosted up to the nominal required voltages, and anything more is truncated down to those same voltages. So, to properly power the motherboard for example, it requires perhaps as many as several different voltages, but the overriding voltage is 5V +/- 5%.
The battery used in this device operates "safely" within a range of 4.2V down to 3.0V. Anything more stresses the battery, which is why the charger interrupts charging once the battery reaches the target voltage which results in a nominal maximum voltage of about 4.2V. It may actually reach a higher voltage during the end of the charging cycle, but after charging is interrupted, the battery goes through a "balancing" where the voltages "settle" down to the nominal 4.2V which is considered the maximum safe voltage for charge. It's easier to regulate the power to one voltage when the supply voltage remains relatively stable within a range, so for our purposes these batteries are a very good power source - but not perfect (yet).
When using the battery, there is what is known as a voltage curve or line (depending on the type of battery and application). Imagine drawing a line that runs from the top of the 10 story building at one end of the block to the street level at the other end. You'd end up with a line that is we'll say diagonal starting high in the sky at one end of the block and ends at ground level at the other end. It would be nice if batteries discharged in such a straight line (Voltage) over that time frame (length of the block), but unfortunately they don't. Some are more straight than others, some have parts of their discharge cycle that look more like a free-fall than a gradual decent.
In the case of Lithium Ion Polymer Pouch Cells (which is what we have in our RAZRs and MAXXs), it has a line that starts out high (4.2V), but drops pretty quickly (first 10% - 15%) down to a stable level (4V), then slowly declines from there to about 20% (3.4V), where it then starts to drop again quickly through the last 20% to the cutoff voltage (3.0V). This following chart shows this, but the chart was designed to show more importantly how to get the longest life out of a LIPO battery.
You'll notice the charge starts off at a much lower voltage in this example, actually 3.8V, but you will also see the characteristic rapid drop of voltage over the early portion of use immediately after charge, and then you'll see after the long slow drop, the range called the "temptation zone". This chart is saying that if you charge to a lower maximum voltage - not the 4.2V that the phone reaches at 100%, but perhaps the 3.8V showing here, which would be about 75% of rated capacity, and then you only use it till it reaches the beginning of the rapid drop, the "temptation zone", you'll prolong the life of the battery significantly.
Now for disclosure purposes, this battery is being heavily loaded in the chart to a rate of power consumption that will be much higher than the RAZR/RAZR MAXX phones will use, so the result for the phone is that the line would be MUCH longer from left to right. Also, this is for a battery that's about 42% of the size of our MAXX cells (1,400mAh versus for the MAXX 3,300mAh), and about 80% of the size of the RAZR batteries (about 1,780mAh or 79%), so the chart for our batteries would look comparable in Voltage but significantly different in Amperage. Finally, they aren't charging to 100% of rated capacity, but instead to about 80% (3.8V), so they are already preventing the stresses at the top of the charge, and the chart is telling you to also stay out of the bottom of the charge, to obtain the best ratio of lifespan with run times.
Click on pic to see full-size.
SO, we see that if the phone's charging system wants two easy values to set the flags at, obviously the first flag will be set at a full charge (100%) since that's what 99% of the users will do, but if the manufacturer wants you to start charging the phone at 15% (as it indicates on the screen when you get there), and to avoid the "temptation zone", then it needs to set the low level flag at 15%, otherwise it would never set the low level flag since the user would never let it discharge to say 10%, or 5%, or God forbid, 0%. In other words, if the low level flag was set lower, then they'd have to set the warning lower to match. They don't want you running in that "temptation zone", so what better way to *(hopefully)* convince you to stay out of there than to pop up a screen warning, bong and tell you to plug in?
In all seriousness, I owe dang near all of my knowledge on batteries to FoxKat. i may simplfy it a bit, but I read the posts and apply what I learn. Thank you for sharing the knowledge so that people like myself can spread the word. :hail: