Just as the title says but for a few more specifics, was thinking a Proto 0-6-0, remember it needs a decoder in there too but lets just asume the smallest decoder for this engine. And how long would it last in discharge mode.
As big as fits? Measure the available space and compare specs on factory keep alive units, and if you want, capacitors from electronci suppliers. Supercaps tend to only come in 5V maximum, 2.7V is quite common, so you need multiples to handle DCC voltage. You wire them in series to increase voltage, but that reduces total capacitance. Nice thing about doign it yourself, you can put a few caps over here, a few mor over there as needed. The factory ones you can take apart, but they come all neatly shrink wrapped.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Make sure the tender has pickups. That will help the most. Not all p2k steam had them in the tender.
After that, I would use CurrentKeeper, or KA-1 attached to your decoder. How long it stays alive is dependent on how much power your loco is consuming.
But to be honest I'm running Bachmann's 0-6-0T's through turnouts and 660uF is more than enough for me. (That's 3 25V 220uF capacitors in parallel) I lay them on their side in the cab roof on right side, and the decoder on the left roof side. I then paint them both block to help hide them. I have to ditch the driver and firemen though.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
You do realize a steam loco without an engineer and fireman can't run...
Mike C.
Sure it can. The real question is how far it can get before it derails, hits something, the fire dies, or it runs out of water and explodes.
rrinker Sure it can. The real question is how far it can get before it derails, hits something, the fire dies, or it runs out of water and explodes. --Randy
At least someone has a sense of humor.
Keep in mind you can get a (non-sound) TCS decoder with the "keep alive" built in. It's only a little larger than one of their standard decoders. It works very well but if the power is cut the engine will only run for about 2-3 seconds. With the separate "keep alive" unit, which has greater capacity, it's quite a bit longer.
Walthers HO Plymouth switcher uses an ESU decoder with it's version of 'keep alive' technology.
https://www.walthers.com/ml-8
The new release will use an ESU motor decoder - the already released ones use a Soundtraxx motor decoder with their keep alive.
All I know is that with todays small decoders, there is a heck of alot of room in the tender on one of these.