Re: Ruined Kestrel by bad batteries
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: HeroFish</div><div class="ubbcode-body">It seems like there are two issue:
1. recording data when the screen is off
2. battery corrosion
I can't see how they are really related (though I am not an Electrical Engineer). However if long term constant drain always causes corrosion, then all my smoke detectors for instance would have corrosion. I just don't see how the long term data recording makes corroding batteries Kestrel's fault, logically or theoretically. It seems to me much more likely to be the battery manufacturers fault - since that is the component that is leaking. </div></div>
They can be related. The discharge condition and rate changes the (alkaline) battery chemistry to release gas from the electrolyte that the mass-produced disposable case can't handle. Depleted alkaline batteries from continuous significant discharge are prone to this. Once the case is compromised, the outside air supplies the CO2 component to make that white crap that will oxidize or corrode copper and PCB connections.
Smoke detectors have a low averaged pulsed current draw rate and more often use batteries with a higher mW/hr capacity (~2x with a 9V) or cells vs. working voltage. Importantly; smoke detectors also warn the occupants of a low battery with the annoying chirp well before full battery discharge/depletion. As far as fault; designs can implement a load-switch or if the quiescent current draw is low enough in an inactive state; go to permanent sleep to prevent full discharge of the cell(s). It takes 200uA over 6months to deplete a lower banner capacity 3V/2AA cells. That is very substantial “off” current so I am not sure what the kestrel is doing. 100mA for 100mS once per hour (large for a sensor sample) over 6mo at working voltage is only a small AA capacity hit.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jerseymike</div><div class="ubbcode-body">Just looked at my piggy back battery pack for my shot timer.
Awesome!! </div></div>
Don't mix battery brands, type (chemistry), and age/condition. The ESR (basically the series resistance in battery model) and capacity of different batteries can vary. Even in series configuration, one battery can end up taking more of a hit to maintain voltage and supply current, even if a small current. The lower series resistance cell (usually “higher” quality), ends up being more discharged over prolonged periods. This is more of an issue with parallel cells but can be an issue both ways.
Common with many things, storage in elevated temperatures will add to the potential issue. Using lithium chemistry AA photo cells is a good recommendation. Using Li rechargeable AA cells wouldn’t be recommended as it appears the discharge of the Kestrel would compromise their capacity over time from discharge if left in.
