Lately Iíve been studying up on using capacitors as energy storage backup for DCC. This is just going to be a catch-all for info I have found. Itís an interesting topic that I canít seem to find a whole lot of information about.
First, ts useful to understand how capacitance is measured. 1 farad is equal to 1,000,000 micro farad, or uf. So if a capacitor is rated at 0.1 uf thatís 100,000 uf.
This is the DCCwiki article: http://www.dccwiki.com/Energy_Storage
Next another article showing some different types: http://www.members.optusnet.com.au/mainnorth/alive.htm
Types of capacitors include:
Electrolytic capacitor- this is the basic type of capacitor that is included with Soundtraxx Tsunami sound decoders (220 uf). Useful for keeping sound decoders from resetting. Even in the 4700 uf range, can only supply backup voltage for a fraction of a second.
Tantalum capacitors- these are compact capacitors, typically around 7x4x4mm. Can be wired together in parallel to form a compact package. Handy for installations where electrolytic caps are too large, but a small amount of capacitance is still desirable.
Double layer, gold, super capacitors, etc- these capacitors have lower voltages, but much higher capacitance. These are what TCS uses for their keep alives. For example the KA1 uses 6 X 220,000 uf super capacitors at 2.5 volts each, wired in series, for a total keep alive capacitance of 36,667 uf at 15 volts.
The KA1 provides a whopping 200,000 uf at 13.5 volts.
So anyway, thatís what Iíve dug up, without doing any actual experimenting myself. Iíd like to hear from anyone that has some experience with stay alives, what kind, what capacitance and the results. Iíll post my own results here from time to time.