Always light with DCC Controler on DC Trains?

[Sascha]

I read in another forum (cant find it anymore),that if you use a DCC Controler with a DC layout, that the lights of the trains will always be on.So would it work with the Tomix 5502 controller ?

[kvp]

If you use a DCC controller with DC trains, the motors in the trains will burn out as the DCC signal is bipolar and just heats up the motors, but does not move them. Also the head/tail lights will light up at the same time, quite brightly because of the overvoltage before burning out a bit later. There is an option for some DCC systems, called zero stretching, that allows DC trains to move on a DCC layout, but this also damages the motors (especially 12V only Tomix/Tomytec/Modemo motors) and the same head/tail light problem remains. Some trains would get damaged immediately, some only after a few minutes.

 

However the Tomix 5502 controller is a DC controller with PWM - CL modulation. It's safe for DC trains, since the signal is pulsed DC. It allows the trains to have all their lights on, even when stationary, but head/tail lights work correctly and light up depending on the direction and does not burn out. (the PWM - CL signal is dangerous for some DCC trains though) If you have DC trains, then the Tomix CL controllers are a good choice.

 

The best advice is to never mix DC and DCC trains unless running them both from a simple linear DC pack, like a Kato throttle.

 

Summary:

-DC linear: 0-12V analog (Kato)

-DC PWM: 12V pulsed, low frequency

-DC PWM-CL: 12V pulsed, high frequency with constant lighting (Tomix)

-DCC: 14-16V, digital square wave (only usable with digital decoder equipped trains)

[Sascha]

Thank you so much. That is awesome news.!!

[Welshbloke]

Some DCC systems can control a single DC loco. I have no idea how it works technically but it does work, with some caveats. Basically I wouldn't use it for anything other than to quickly confirm a loco is working before fitting a decoder.

 

I have heard that it can damage more exotic motors like coreless motors, and one chap I know was most indignant that a plunger pickup on a loco had melted after he left it parked on DCC-powered track for an extended period as the lone DC loco.

 

I built a PWM controller for a few quid using parts from ebay and an electronics shop. The important bit is a DC motor control board which cost me about £3 from an ebay seller in China, it can handle up to 24v DC input. I use an old mains transformer with a 12v DC output to power it, and a DPDT switch to enable the trains to reverse. The whole thing fits into a small project box as a handheld controller, with a Kato power cable hanging out through a grommet (to plug the Unitrack feed wire into) and an input socket for the mains adapter. I've left it running a twin motor Tomix Shinkansen for hours before now and it shows no signs of melting or blowing up, the worst that happens is the transformer getting warm. The lights come on brightly at low speed.

[kvp]

Some DCC systems can control a single DC loco. I have no idea how it works technically but it does work, with some caveats. Basically I wouldn't use it for anything other than to quickly confirm a loco is working before fitting a decoder.

I have heard that it can damage more exotic motors like coreless motors, and one chap I know was most indignant that a plunger pickup on a loco had melted after he left it parked on DCC-powered track for an extended period as the lone DC loco.

The DCC system can distort the DCC wave to shift the balance between the two sides. This causes a DC level to appear on top of the DCC-s variable polarity wave. It's like connecting a car to a standard car battery and an AC outlet at the same time. The car might start up or just burn to a crisp under the AC power. This is a seriously bad idea and this is the reason why the DCC standard doesn't have it as an option. (only states that DCC decoders must tolerate it, but it never said that DC locos will tolerate it too) For old, high current and high voltage (>16V) european DC motors DCC's zero stretching mode might be survivable, but for modern low current 12V DC motors used by most japanese manufacturers, it's dangerous.

 

That home made PWM controller is the low frequency PWM one that doesn't have a constant lighting circuit. (2nd in my list) It's good for all DC (except for really low voltage motors) and only a very minimal speed is required for the lights to start up. Stationary lighting is not supported though, but it's very easy and cheap to make and have excellent slow speed running.

[inobu]

The means of operating 1 DC train on a DCC system is called Zero stretching. As kvp pointed out DCC has a positive and negative wave form representing 0 and 1. To a DC train this is forward and reverse. what Zero streching does is send  only the Zero transition which the DC train sees only one direction. Therefore operated some what normally. 

 

Easier to just connect a DC transformer if you are going to run DC

 

Inobu

Edited September 20, 2015 by inobu

[kvp]

DCC signals use short and long pulses of positive and negative signals. A short + and - is 1, a long + and - is 0. The positive or negative part of the 0-s are held longer for the DC motors, but the 1-s and the other part of the 0-s are still sent out. It's like switching direction on a DC controller several thousand times a second, with one direction being held a bit longer to move the train. It's very bad for the DC motors. Also the DCC signal is usually above 12V, which is overvoltage for the unprotected motors and any analog lighting circuits. Most of the time, the motor coils are in high starting current mode, like turning a DC controller above the top safe value then holding the locomotive wheels down to prevent them from turning. Some locomotives survive both for a longer time, but some don't. Going slow in this mode is even worse as the percent of reverse current is higher and gets the highest 50% when the locomotive is stopped. (it's stopped by switching it into forward and backward for the same amount of time every second, it's effectively buzzing in place)

[HantuBlauLOL]

Just buy CL controller, or build it by yourself. Not that hard imho

[Welshbloke]

That home made PWM controller is the low frequency PWM one that doesn't have a constant lighting circuit. (2nd in my list) It's good for all DC (except for really low voltage motors) and only a very minimal speed is required for the lights to start up. Stationary lighting is not supported though, but it's very easy and cheap to make and have excellent slow speed running.

 

Depends on the train, at least with the board I used. I don't think it actually drops to 0v even with the controller turned right down, as the headlights on my Tomix locos glow faintly whenever the power is on. Obviously they get brighter as you pick up speed, but they're reasonably bright at a sensible speed (as opposed to some models and transformers where you need to be attempting the rail speed record before the headlights are visible). I'm slightly tempted to have a go at building another with a different board, as there seem to be a few designs about.

 

Informative explanation of how Lenz controllers manage to run a lone DC loco on DCC too, thanks! Like I said, the only time I'd do it is as a quick test run to make sure a loco is working before converting. I have no intention of converting my N scale fleet as it looks fiendishly complicated and is obviously an all-or-nothing deal, the only locos I've converted before were some HO scale US outline diesels, a few Marklin locos with ESU decoders (which understand DC, AC, DCC and Motorola formats) and a couple of G scale locos. Some were quite involved conversions with remote controlled uncoupling and assorted lights, but in HO you have a lot more space to work than in N!