[quote="bigglez"]You probably have enough data
to construct a timeline of the power demands, and
use these to find the energy drawn from the battery,
the predicted solar recharge energy, and account
for losses in the converter and regulator. This R&D
work will bring you to a high confidence on the
Yup, I just need to sit down and work out the details there, been estimating numbers to this point, though I've a reasonable degree of confidence that its achievable.
[quote="bigglez"]Perhaps a Li-Po or Li-Ion cell is not required. It might
be possible to use a single NiCad or NiMH cell with
a battery booster IC. These cells are cheaper and
may only require replacement after a long service life.[/quote]
Hmmm... I wanted a high voltage single cell battery that is light, high capacity, and has low self discharge characteristics, that pointed me at Lithium-polymer and most of the docs I read indicate that they are also not susceptible to the memory effect of bad charging practices that Nickel (cd or mh) based batteries suffer from, they also have a pretty wide thermal range too... important for sitting in the California heat duriung the day or the -30F temps at 18000ft (or the English hangar in winter). for hours on end.
(I fly here in California for the high temp testing, but my dad flys in England where the lower scale temps are available for 'soak' testing
[quote="bigglez"]I'd take a look at the major analogue IC houses
(ADI, Linear Tech, Maxim/Dallas, NSM, TI, etc.)
as they have produced several "single and dual
cell" PSU controllers for the phone and PDA
Yup you read my mind, that what I'm looking at, unfortunately most (all) of the nice small charger IC's are designed for use in portable devices where the expectation is that they be charged from a USB port which provides a nice fat 5V supply... I need to get there from the solar cell so I'm back to my voltage pump, maxim makes plenty of claims about their IC line for this stuff, I'll take a closer look. I may actually use the processor to decide whether the cell is producing enough power and then turn on the charge circuit interactively rather than just leave it connected permanently and hope it does the right thing at low power levels, need to check whether I have enough analogue/digital ports to support that, but that could remove any bad behavior exhibited by the charge IC at lower than ideal power levels.
[quote="bigglez"]One other thought I had was adding a separate
RTC IC (with it's own 32kHz Xtal and button cell
Actually the PIC U;m using supplies an RTC function with the addition of a 32khz crystal, and I'm using a fairly large serial EEPROM to hold the logged data just in case I need to hold months worth of data before I can contact a base station, it makes my code a little more compicated but I like a challenge. My savior here would be the base station, if I can ever get a link to it from the aircraft device (I expect to do this in the hangar over night), it can re-sync times and not rely totally on the RTC function, the important thing is flight elapsed times, not so much time of day or date (though reasonable accuracy would be great), I need to again figure out if the PIC RTC is accurate enough over months to support this without a re-sync or needing a dedicated device.
Thanks for the comments, its great to discuss this with another mind, its helping me answer my own questions....wait till I talk to you about the bigger project I'm working on that allows me to procrastinate on this one...