Hi, hoping for a little help to choose the correct capacitor for my project.
I am modifying a remote control wall switch to be wifi enabled, using an electric imp.
I am trying to use the already present power supply in the wall plug which is 5v @ 25ma. The electric imp needs up to 400mA for a few seconds during startup, genrally max 250ma during transmission burst and during use between 10mA and 6µA.
Edit: I just remembered to add that the relay that controls the switch also will not latch when the imp is trying to start, thats another reason I thought of using a large capacitor.
In order to supply power during the high current draw times, I thought about using a high capacity capacitor just like used in the Adafruit Tweet-a-Watt, where a 10,000µF @6.3v.
The imp needs a 3.3V supply but the power regulator can take in anything up to 17V.
I did do electronics at school but can not remember there being so many equations to pick the right capacitor as I have found online, so am a little confused.
Looking online I see that capacitors have a pretty quick voltage drop curve.
So my questions are:
Can I assume the voltage drop on a large capacitor be ignored when such little current is being drawn, as it will not move far from the filled capacity end of the graph once charged?
I have seen caps have a max working voltage. Does this mean that caps begin to discharge at the voltage they were charged at, and then drop, or will they always begin discharging with a specified discharge voltage.
Based on my assumptions that a high-capacity, low draw circuit (once charged) output should be fairly steady, and voltage is same as charging would a component such as N99CN from http://www.maplin.co.uk/double-layer-backup-capacitors-98185
would do the trick, also as they are described as an alternative to backup batteries I would assume they are suitable.
If there are any good guides to capacitors you could point me to I would be grateful as I am keen to learn as much as possible. Since school I have done nothing electronics related until the last few months where I have been doing a couple of small projects.
Also I have found a capacitor charge/discharge time calculator, but it asks for circuit resistance, when is the best time to measure this, as the current draw changes when its on I would have thought the resistance also does.
I have noticed I have said assume a lot, where in fact I mean more of an educated guess, again any pointers, tutorials or suggestions would be really appreciated.