The Museum of HP Calculators

HP Forum Archive 20

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #2 Posted by Kees Bouw on 29 Jan 2012, 2:22 p.m.,in response to message #1 by Jeff O. As I understand it, pressing a key on the 15C LE draws quite a lot of current. Testing battery life by just running programs therefore may not be accurate, because not many keys will be pressed.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #3 Posted by Jeff O. on 29 Jan 2012, 3:31 p.m.,in response to message #2 by Kees Bouw My understanding is that holding a key down draws the same current as a running program. If each key press is roughly 0.5 seconds, it would take 118,800 keypresses to equal 16.5 hours of run time. I'm not saying that the two uses are equivalent, as perhaps it is harder on the batteries to draw 10.5 mA in 118,800 0.5 second pulses than in 60 16.5 minute pulses.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #4 Posted by Lode on 29 Jan 2012, 2:42 p.m.,in response to message #1 by Jeff O. It would be interesting to measure how long it takes a fresh set of batteries to be depleted if all you do is continiously hold down a key :)

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #5 Posted by Jeff O. on 29 Jan 2012, 3:33 p.m.,in response to message #4 by Lode My understanding is that holding a key down draws the same current as a running program. So it should presumably be the same as if you just ran a program continuously. I did not test that, so I cannot say.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #6 Posted by Paulo MO on 29 Jan 2012, 3:39 p.m.,in response to message #4 by Lode AFAIK, the high current draw on key press is the result of setting the processor at full speed whenever a key is detected (to ensure a fast reaction to key press). Hence, as Jeff points out, pressing a key, or running a program at full processor speed should amount to the same.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #7 Posted by Kees Bouw on 30 Jan 2012, 7:57 a.m.,in response to message #6 by Paulo MO Quote: AFAIK, the high current draw on key press is the result of setting the processor at full speed whenever a key is detected (to ensure a fast reaction to key press). Hence, as Jeff points out, pressing a key, or running a program at full processor speed should amount to the same. In the 15C LE Bug Report, Katie writes: "Current draw is over 20ma when holding down a key, leading to rapid battery depletion. While not a bug this is fixable in firmware and does not happen on the 12C+." But if it is done purposely (to ensure a fast reaction to a key-press) should it be fixed ? And why does it not happen in the 12C+ ? Or is the problem only in the "holding down" (if so, it can't be a serious problem, because mostly keys are just pressed and not held down). Edited: 30 Jan 2012, 8:02 a.m.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #8 Posted by Jeff O. on 30 Jan 2012, 12:43 p.m.,in response to message #7 by Kees Bouw According to this post by Cyrille de Brébisson: Quote: the 12C emulator, in order to try to preserve power usually tells the calculator that the keys are released instantaneously. this avoid a dead loop waiting for the key to release in the 12C ROM and the power use associated with that... It sounds like in the 12C+, pressing a key runs the processor at full speed for an instant, then the emulation layer tells the processor that the key has been released whether it has been released or not. So apparently you will get fast response to a key press without continuous high-current draw.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #9 Posted by Gerson W. Barbosa on 29 Jan 2012, 8:28 p.m.,in response to message #1 by Jeff O. Great experiment! I tried to run a program that would take about six hours to run, but after 2 hours and 40 minutes I noticed the display was dim. I stopped the program and waited five minutes before continuing, so the batteries recovered. When I checked again half an hour later the display was blank and the program had gone (Pr Error). I used the original Panasonic cells that came with the calculator, both at 3.039V each in the beginning and 2.803V and 2.808V when I measured their voltages again as soon as I noticed the calculator was off. Probably the HP-15C LE had worked for about 10 or 15 minutes before turning itself off. This means it cannot run a program continuously for more than three hours. I had barely used the calculator, but I may repeat the test with fresh cells tomorrow to be sure.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #10 Posted by Jeff O. on 29 Jan 2012, 9:56 p.m.,in response to message #9 by Gerson W. Barbosa How many steps is your program? I might want to test another set.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #11 Posted by Gerson W. Barbosa on 30 Jan 2012, 6:46 a.m.,in response to message #10 by Jeff O. 74 four steps. That's the listing in the message #19 of this thread. Perhaps the less efficient way to solve Karl Schneider's arithmetical challenge :-) ----- Update: actual running time is shorter than I thought, about three and a half hours (would have to check it again). Edited: 30 Jan 2012, 5:16 p.m.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #12 Posted by Bruce Zastera on 29 Jan 2012, 10:45 p.m.,in response to message #9 by Gerson W. Barbosa Quote: Great experiment! I tried to run a program that would take about six hours to run, but after 2 hours and 40 minutes I noticed the display was dim. I stopped the program and waited five minutes before continuing, so the batteries recovered. When I checked again half an hour later the display was blank and the program had gone (Pr Error). I used the original Panasonic cells that came with the calculator, both at 3.039V each in the beginning and 2.803V and 2.808V when I measured their voltages again as soon as I noticed the calculator was off. Probably the HP-15C LE had worked for about 10 or 15 minutes before turning itself off. This means it cannot run a program continuously for more than three hours. I had barely used the calculator, but I may repeat the test with fresh cells tomorrow to be sure. So you couldn't run it for 3 hours continuously, but Jeff O. ran it for 16.5 hours running in intervals. Does running in intervals make that big of a difference to battery life, or is this because your program draws more current than his?

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #13 Posted by Katie Wasserman on 29 Jan 2012, 10:56 p.m.,in response to message #12 by Bruce Zastera Running in intervals is much better for battery life (lithium coin cells in particular) than running continuously. Indeed Jeff's rough calculation of the number of keystrokes based on 16.5 hours of battery life might be on the low side. What greatly surprises me about Jeff's measurements is that he got 75% of the rated capacity on these cells even though they are being run at 100 times the rated current draw. These are super cells! What doesn't surprise me is the horrible way the 15C LE and 12C+ just die when the cells are exhausted wiping out memory. There's no good reason why they can't shut down gracefully when low voltage is detected.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #14 Posted by Lyuka on 29 Jan 2012, 11:07 p.m.,in response to message #13 by Katie Wasserman Quote: There's no good reason why they can't shut down gracefully when low voltage is detected. As the name implies - HP 15 Continuity Limited Edition. BTW, by the data sheet of Panasonic's CR-2032, though its capacity is rated at standard discharge current of 200uA, the characteristics is specified from relatively heavy load of 1Kohm(3mA) The data sheet of Maxell's CR-2032 shows very heavy load (300ohm, 5sec) pulse discharge characteristics. Its capacity under that condition is 160mAh(Ta=25) at terminal voltage of 2.5V. It's 70% (160mAh/230mAh) of nominal capacity. The data sheet of Energizer's CR-2032 shows very aggressive load (100ohm, 2sec) pulse discharge characteristics. Its capacity under 400ohm, 2sec * 12 times / day condition is 220mAh(Ta=25) at terminal voltage of 2.5V. It's 97% (220mAh/230mAh) of nomninal capacity. IMHO, Li-Mn batteries from these three brand have both reliability and surprising high performance. Lyuka typo corrected: 100ohm, 2sec -> 400ohm, 2sec Edited: 30 Jan 2012, 4:02 a.m. after one or more responses were posted

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #15 Posted by Katie Wasserman on 30 Jan 2012, 2:31 a.m.,in response to message #14 by Lyuka Quote: The data sheet of Energizer's CR-2032 shows very aggressive load (100ohm, 2sec) pulse discharge characteristics. Its capacity under 100ohm, 2sec * 12 times / day condition is 220mAh(Ta=25) at terminal voltage of 2.5V. I see that here. but it's 400 ohms not 100. At higher currents things get much worse: 1 msec on and 14 msec off pulsed load of 23ma which yields 150mah with a terminal voltage of 2.4. Which is only 62% of nominal capacity. Jeff's test was at 10ma per cell with a pulse that's 16 minutes, nearly 1 million times longer than the short spec sheet pulse and 480 times longer than the long spec sheet pulse. I think Jeff's batteries were far better than the spec sheets indicate. I suspect that there's something to having two cells in parallel that allows the combination to do better than the sum of the parts.

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #16 Posted by Lyuka on 30 Jan 2012, 3:58 a.m.,in response to message #15 by Katie Wasserman Quote: I see that here. but it's 400 ohms not 100. It was my mistake. 400 ohms is correct. I'll correct my post later. Lyuka

 Re: Capacity of the CR2032 Batteries as used in the 15c LEMessage #17 Posted by Gerson W. Barbosa on 30 Jan 2012, 5:12 p.m.,in response to message #12 by Bruce Zastera Quote: So you couldn't run it for 3 hours continuously, but Jeff O. ran it for 16.5 hours running in intervals. Does running in intervals make that big of a difference to battery life, or is this because your program draws more current than his? Running in intervals does make a difference, as Katie said. However the original Panasonic cells were not as fresh as I imagined, so the actual capacity is longer. I've repeated the test succesfully with brand-new maxell cells (initial voltages 3.270V and 3.267V). I was expecting the program to run for 5 hours and 40 minutes, but it didn't take that much time. I checked the display after 3 hours and 5 minutes and didn't notice anything wrong. When I checked it later, the calculator was off. I turned it on and was prepared to see the "Pr Error" message. Instead it displayed the expected result: 534,912,768.0. The chronometer was stopped at 03h52m35s. I don't know long it actually took. Final voltages were 2.874 on both cells (actual voltages were lower, since they had had some time to recover). My multimeter has a serial interface, but unfortunately the software doesn't run on Vista OS. A discharge curve would be nice, but I am not willing to do this manually. Edited: 30 Jan 2012, 5:25 p.m.

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