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I did this at one point. I was already running fixed polarity fixed voltage on the track (24.5) volts. This made it easy to trickle charge a 19.2V battery pack with a 1 ohm resistor figuring in losses for the needed bridge rectifier between the track & the batter pack. But you also need a diode in parallell with the resistor for the electrons to flow thru when running off of battery power (as opposed to the resistor), so that drops your effective voltage from the pack enough so that you do notice when dirty track causes the failover to battery power.

Also, at a trickle charge, the batteries rarely get a chance to fully re-charge, unless you leave the loco on a powered siding overnight, meaning they will eventually run down & require taking out, or taking the loco inside to charge, depending on how you have it setup.

So in the end, it ends up being more work for less satisfaction that just going battery, IMHO.
 

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Posted By DKRickman on 06/06/2008 9:02 PM
Has anyone tried getting rid of the batteries entirely? Keep a constant fixed voltage on the rails, which provides power directly to the R/C reciever in place of the batteries. A fair sized capacitor could be useful to bridge any dead spots in the track. Basically, it would function like a DCC system, with all the wiring simplifications, but with radio control instead of digital commands through the rails. It would even be possible to run high voltage (greater than 24V) AC, with it's inherent advantages regarding lower resistance losses, and step it down with a transformer inside the loco.




Yes, this is how I ran exclusively, up until recently. Constant polarity fixed voltage on the rails simplifies a lot of things.. like reversing sections (Y or loop) & I came up with a simple relay based detector/reverser for that. It also allows, with multiple receivers, independent multi-loco operation, in either direction, which is fun provided you have good passing sidings. I used Aristocraft on-board TE receivers.


I also setup capacitor based backups for a few locos... some, which had power sharing from multiple dedicated powered passenger cars, did not really need it, as the higher voltage on the rails (in my case 24.5VDC) made power pickup problems few.


However, for short-wheelbase locos, or locos that never ran with other powered locos or trail cars, capacitor based power-backup helps a lot. But it's tough to get enough capacitance to really make up for more than very short power interuptions. IIRC, i used 3 or 4 2500 mf capacitors in parallell, & these would still not do much more than provide enough "umpf" to get over short dirty spots. (That is still pretty nice though).

As far as running AC, & voltages greater than 24V, I think you would run afoul of local ordinances there, as 24V is usually the cut-off for a "low-voltage" system. Check it out though. I don't think much would be gained from any higher voltage, plus having to rectifiy the AC, then regulate it down (with a voltage regulator rather than a transformer) would just add more unneccesary steps/complications. 24V tolerates a lot of bad track joints, dirty track etc., without being high enough to really hurt anything/anyone if they short the tracks. That said a screwdriver will certainly try to weld itself down, a wet frog gets frozen in place if he touches both rails & operators with sweaty t-shirts who in-advertendly lay across the tracks get a pretty good shock. If you do AC or even DC, don't forget to have bridge rectifier in between the track pickups & your capacitors (changing direction of the loco would flip the polarity fed to the capacitors.) I also put a resistor in line to slow the capacitor recharge to prevent mega-amp draws that would cause wheel-arcing, wire-heating, etc.


FWIW, even with a track cleaner, I found that wheels get dirty often enough to be a pain, & since my dog seemed determined to chew in half any exposed track-feeders, I've since gone battery. I'm not saying it's better, but once you start messing with charging on-board batteries or providing on-board capacitance, it is just almost easier to go battery. MY run times got progressively shorter as well, making the run-times from battery packs totally acceptable.
 
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