Any experience of using supercapacitors in GSM/3G environment? I have been thinking of possibly using one, in search of relaxed power supply specs and smaller overall size of GSM equipped products.
Usually, the idle consumption of a GSM module is something like 20 mA, or even less, but during occasional transmit period you need 100 times more, up to 2 A.
Taken the short lasting need for this superfluous current, it is basically crazy to build a 2 Amp power, to be fully loaded for something like 1 % of the time.
Of course, supercaps are not too cheap, and they are ususally not second sourced, and they are sensitive to overvoltage, etc., so there isa number of penalties involved.
And one thing: can they actually provide current fast enough, due to internal resistance?
I would very much appreciate any thoughts or experience shared in this topic.
Thanks and best regards,
This is a very interesting topic.As you highlighted, a GSM/GPRS modules consumes high peak of current ( as high as 2 A ) only for a limited time slot due to burst transmission.There are no reason to design a power supply circuit with this high current capabilitysince for most of the time it will be overestimate.
So the need of a device which will be able to supply such an extra current during Tx slotwhile accumulating energy during low absorption time.
The choice could be either a supercap or also a normal high capacity capacitor, so what to be used?Supercaps are usually Voltage limited so it is not a good idea to use them, and since they are really expensive this is a good news 🙂
A normal tantalum, low ESR capacitor, rated to twice the VBatt does the job very well.
Attached it can be found an excell sheet (need to have macro enabled ) I wrote to calculate the capacitance needed after set up the Vmin level of VBatt, the Vout of regulator,current limitation ESR and other minor points.
"great minds think alike" if you can excuse me for quoting this 🙂
Thank you for the spreadsheet, I was thinking of setting up something similar but will now use yours, at least as s starter. Just thinking: some added resistance in the leg from cap to module? Traces of PCB, solder joints and others, i.e. unwanted resistance…
Great if one can do with "standard" capacitors, although tantalum is also somewhat problematic. But there are others, like organic electrolytic caps etc.
In case you need to send the "last gasp" (as SMS) after power outage, and do not want batteries, you may still need to look at supercaps, though. But that is slightly another story.
I will think about this…
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