|Re: Another HP-15C LE bug? --> serious power management bug|
Message #43 Posted by robert rozee on 3 Oct 2011, 9:05 a.m.,
in response to message #41 by Katie Wasserman
have just been looking over datasheets for various brands of CR2032 cells. to cut a long story short, the MAXIMUM continuous current draw allowed by any manufacturer seems to be 3mA. given two cells in parallel, this translates to a MAXIMUM of 6mA total current draw by the 12C or 15C calculator.
at 3mA from each cell, the normal CR2032 capacity of 210mAh will be reduced 150mAh at an operating temperature is 23 degrees C. so one would expect a 'running' time of 50 hours [based upon CR2032 datasheet from Mitsubishi]
up at the 20mA level - 10mA per cell - the storage capacity of the cell will (based upon projecting up from lower current drain characteristics) will be almost nothing. that is, if the cell is empty within minutes is will be due to NO fault of the cell manufacturer nor any cell design fault. quite simply, this discharge rate is outside of operating specs (the closet i can find is a pulse discharge of 15mA for 15 seconds, with no ratings provided below a 2.6v terminal voltage - this is perhaps why low voltage sensing is turned off in the firmware!!).
as i follow the unfolding of other's follies, i hear a mantra playing in the background:
THERE ARE NO FREE LUNCHES. THERE ARE NO FREE LUNCHES. THERE ARE NO FREE LUNCHES. THERE ARE NO FREE LUNCHES. THERE ARE NO FREE LUNCHES. THERE ARE NO FREE LUNCHES. THERE ARE NO FREE LUNCHES. THERE ARE NO FREE LUNCHES. THERE ARE NO FREE LUNCHES. THERE ARE NO FREE LUNCHES.
the candle that burns brighter burns out proportionately quicker. in that case, it burns out even quicker still. the only sane engineering solution is for HP to release firmware for the new 12C and 15C calculators that limits speed such that current drain remains below 3mA per cell (6mA in total). it would be prudent to limit the current drain even further.
this would, of course, mean that your shiny 'new' calculator is only a paltry 10x faster than the old one - but at least it then might give accurate numeric results...