MichaelN wrote:Even if you could get them in that rating, I’d be hesitant to use SMD supercaps for a couple of reasons:
- They would be more heat sensitive than other components, so you’d need to be very careful soldering them.
- I don’t like using “large” SMD compoents that are only supported by a couple of small pads. The weight of the component can pull the pads off due to shock or vibration.
Well heat sensitivity, would just mean I'd have to solder by hand, and the small pad problem is solved by adding some vias to connect to another pad on the bottom. That prevents the pad from peeling up for a large part (technically it might make it harder to solder, but if the pad on the bottom is small, it wont matter).
Mee_n_Mac wrote:And the above should raise the question that the OP needs to have answered up front ... what's the trade study for using SMD supercap vs good ole Li battery backup ? I can understand the desire to avoid the space and cost of the normal Li charging circuit but does that still hold up ?
Personally, I have space restrictions that prevent me from using a Li battery. I might be able to justify it if I use a backup battery for the entire system, but Li battery for just an RTC is not justifiable for my application. Really the choice is between a coin cell and a supercapacitor. While it is easier to just run with a coin cell battery, I'd prefer to design the device in such a way as to minimize the number of times it needs to be serviced. It needs to operate sometimes remotely on a regular basis. So thats why Im leaning towards the supercapacitor.
However, what if the temperature goes into both extremes, as with very hot summers, and very cold icy winters? Would a coin cell do better or would a supercapacitor? How much would the effect of temperature extremes have an effect on lifespan of the energy storage?
Another question, and this might sound a little redundant, but is there a Li battery or Supercapacitor in the shape of a coil cell that I can optionally remove from the circuit if it fails, rather than SMD the actual energy storage device? Granted this would increase the number of times that the device would need to be serviced, but, still I'd like to know.
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