DCC idea for "power independence"

Reading a thread here about the problems of powering locos across dead sections of track gives me an idea. I may not be the first person to
have come up with this, so let me know if you've heard this before. It also may be impractical for several reasons, discussed below, but I still think it's an interesting idea.
How about building a DCC decoder that uses battery backup for both itself and any powered functions (motor, lights, etc.)? Actually, rather than modifying the decoder itself, this could probably be designed as a power-handling "front end" to the decoder. Here's how I envision it working: it would use a small 12-volt rechargeable battery, which would power it and the loco. The power module would take care of keeping the battery charged from the track voltage, when available, and would draw power preferentially from the tracks, when available.
But when track voltage disappeared, the battery would be used as the power source. So instead of being able just to go over short sections of "dead" track, this could potentially power a loco over good-sized sections of track without power.
*Problems*
1. The battery and power module would have to go somewhere. I'm seeing a rechargeable battery about the size of a 9-volt battery. This would work fairly well in a steam loco, where the battery and the power module could go in the tender. But in an N-scale diesel, forget it.
2. What happens when you shut your layout down at the end of a session? The power module, seeing track power go to zero, would kick in and possibly drain the battery. Not a show-stopper necessarily, but not a good feature. Either it would have to be shut off manually with a switch on the loco, or possibly through the decoder, by sending it a special "shutdown" command. Or there could be a timeout timer that would shut the whole thing down after a short interval.
So whaddya think? Should I pitch this idea to Digitrax?
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snipped-for-privacy@but.us.chickens says...

Check out this train camera that fits inside an N-scale train:
http://www.rfamerica.com/product/industrial/hobby/tc9/index.html
The camera is run from track voltage (4.5 volts and up). The camera is charged while the train is running. When the train stops, the battery powers the camera for about 15 minutes. I am going to use a latching reed switch to turn the battery on/off since it is supposed to be disconnected when not in use.
The battery they use might work for your idea.
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Ken Rice wrote:

You are both overlooking one minor fact. DCC requires a "pulsing signal" and signals to control the decoder via the tracks. Putting battery powered DC directly to the motor and lights would have the train run freely or possibly continue at the same rate (although I'm not sure) with no control.
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Jerry Abrams spake thus:

Ackshooly, I did think of that and was going to address it. You're right: if track power were lost, so too would be the DCC signal, so that even if one could power the decoder from a battery, it would still revert to an inactive state so far as all the devices on the loco were concerned (everything off). So I guess you'd have to rejigger the way the decoder works: how about if you allowed the loco to continue at the last set speed when power is lost, but limited it to a short period, say a few seconds? That way, if the timeout period expired and there was still no DCC signal, it would shut the loco down. (Otherwise, this idea could be Collision City.)
Maybe it's just not practical.
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David Nebenzahl wrote:

After the two track wires on (most) decoders there is a split in the circuitry; signal one way, power the other. The power circuit is rectified, and at that point a large cap could be installed. The only problem would be to limit the current the cap can draw to the maximum rating of the related diodes.
Regards, Greg.P.
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Greg Procter spake thus:

[...]
Yes, but this still doesn't address the problem of what to do when the DCC signal goes away: continue at the same speed? Leave the horn blowing and the light on?
I believe that if you took a standard DCC decoder and hooked it up with a battery backup as I've proposed, when the DCC signal disappears, the decoder would shut everything down, even if you could still supply it with power from the battery.
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<snip>

Not with capacitors, according to Stan Ames. And if anyone should know, it's the guy who literally wrote the book on DCC. I talked with Stan (who does post here from time to time) at the Hub Div. NMRA show in Marlboro, MA just last month at the Lenz demo booth (his wife, Debbie, is an Lenz rep), and I was asking him about flickering headlights in cab control cars (like the MBTA) and how much I hate that. He said that all I had to do was put a capacitor across the diode rectifier that's in every decoder. When I asked him how big a cap, he said, "10". How do I find this rectifier, and how do I determine which leads to solder to?, I asked. He replied that the blue wire was the ground for the decoder, and to put a meter from the blue wire to each of the diode leads until I found one that gave me track voltage. That would be the lead I would attach the cap to, with the other going to the blue wire. I asked him if this would stop my headlights from flickering? He said yes. I asked, "What about the DCC signal?" And he replied that the decoder will keep doing the last thing is was told to do as long as there is power. The cap would provide this power over temporary power interruptions.
Paul A. Cutler III ************* Weather Or No Go New Haven *************
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Jerry Abrams wrote:

JA:
The decoding circuits wouldn't see the battery, just the power circuits. If the track went totally dead, putting the engine entirely on battery power, the decoder would see nothing (and yes, continue at the same rate until told to stop. Sounds like we could have some fun accidents at a dead stop section by that scale drawbridge crossing the aisle, or at the stub terminal with a station built of balsa wood and served by a brass passenger train pulled by 4 Hobbytown E units...:D)
The only difficulty I can see (besides the fun accidents) is sorting out weird frequencies caused by intermittent contact or arcing on track sections that weren't quite dead yet. Though you'd have a tank o'power and not need to rely on the track all the time for that, you'd still have to rely on it for carrying the signal. Cordially yours: Gerard P
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David Nebenzahl wrote:

Battery power and r/c are fairly common in G gauge and there's a British firm (Red ....) that does it in OO. I'm using combined track/battery power in G24 scale.

No problem in G24 scale =8^)

My onboard control electronics reads the track voltage or R/C speed setting (depending on manual switch setting. For track voltage control a resistor capacitor combination feeds the speed control so speed falls away when track voltage is lost, but the rate of deacceleration is such that a few seconds of poor contact is unnoticable.

Why not - either that or fix your track!
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David Nebenzahl wrote:

....
Where have you been for the last couple of years? Lens already has a decoder that does this:
http://lenz.com/techinfo/usp.htm
All their Gold Series decoders have this capability.
peteski
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Peter W. wrote:

Hehe, thanks Peteski.
As I was reading through this thread, each post *without* this revelation was making me more and more surprised. I started thinking, *someone* besides me has to know this!
To add a little additional info, the same concept is often used with sound decoders so they won't drop out and then go through their start-up sequence if there's a minor disruption to their power pickup. The capacitor is clearly visible in the graphic on this Digitrax page:
http://www.digitrax.com/prd_mobdec_sfx064d.php
Stevert
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Peter W. spake thus:

Thanks for that, and for telling me (like I asked right off) that you'd heard this idea before. So it looks like Lenz basically has baked in all the functionality I proposed. Apparently, their decoders just "keep on truckin'" when hitting a dead section of track.
One thing in their description screams for correction, though:
USP allows the decoder to pick up the DCC signal even when there is no electrical contact to the rails.
This is absolute horseshit. When there's no electrical contact, there's no DCC signal, unless they have a radio receiver hidden there, or have perfected some kind of electro-telekinesis technology.
I think what they *mean* is that their technology allows the decoder to continue to operate even when there's no electrical contact from the rails.
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David Nebenzahl wrote:

This response is a little strong. Lenz uses capacitance coupling to detect current flow in the tracks. I have actually seen a demonstration of this first hand. They can drive a loco onto a piece of paper, stop and reverse it while it has all its wheels on the paper.
Cheers, David
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rails.
Perhaps it's by way of induction? Sort of like the old PRR Trainphone... The rails must be giving off some kind of signal, and perhaps the Lenz USP decoders can pick that up? I dunno, but it sounds better than "electro-telekinesis technology". :-)
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Pac Man wrote:

Hey, maybe Stan Ames will find this thread and chime in to explain this technology. Although I suspect it is proprietary and they don' t want to give out details of how it works.
OTOH, it shouldn't be too difficult to buy one of those decoders and reverse engineer it (at least the hardware part). But I supspect that they protect their microcontroller's firmware from being read back.
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David Nebenzahl wrote:

It's no horsheshit. I saw a demo. They use some sort of coupling (don't know if inductive or capacitance) but the loco keeps receiving DCC commands even while riding on tracks covered with paper tape. That along with whatever battery backup they use allows the loco to be fully controlled.
Peteski
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Are "forst part" and "neds" proprietary Lenz technology? *8^)

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Paul Newhouse wrote:

Hey, they're German - give them a break. :-) Peteski
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I did, I smiley faced the comment.
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Paul Newhouse wrote:

...not all smiles and sunshine...
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