Another question from the Telit-newby: Has anyone looked into using a low-ESR supercapacitor paralleled with the battery to help handle the ferocious current spikes? Seems like it would make life so much easier for the battery that a smaller unit would suffice.
Maybe there is a fly in that ointment, anybody know?
I’ve thought about it, but never actually done it. The datasheet says it’s current spikes peak at 2A. The Sparkfun LiPoly batteries are able to source this much, even the small ones, but if you’re having problems still, check that there aren’t any parts between the battery and the module that would limit it under 2A. Particularly, the regulator. I’ve usually had to add several capacitors. I’m not currently using the Telit modules, but if you can look at the spike on a scope, you should be able to apply the right capacitor with the least amount of capacitance necessary to hold the voltage over the time period of the spike. A tantalum cap should work nicely.
The only reason I shy away from supercaps is that they are a lot spendier and harder to find. Maybe someone else has found some that would work well?
I’ve tested it for other situations using the LiPoly. Since battery discharge is wildly nonlinear, using a cap to spread out the current spike actually prolongs battery life. The issue here is knowing how long the ‘spike’ really lasts and whether even a supercap can source it. Just have to hook it up and see.
I’ve looked at the spikes using a scope on a different system where the GSM PC/104 daughter card was causing a system reset, so I know what you’re talking about. It’s pretty bad. We got the random resets to stop by placing caps in all the right spots.
Hybrid batteries are pretty cool. Come to think about it, I remember seeing a graph showing pretty incredible results. I wonder if any hybrids are being marketing yet?