light in locomotive help

Discussion in 'HO Scale Model Trains' started by Wyndigo, Mar 21, 2006.

  1. Wyndigo

    Wyndigo New Member

    just wondering if there is a somewhat simple way to keep the locomotive light burning all the time while running my train, I have searched on here and found a couple of posts about using led's and such, but does anyone have a "simpler" way?
    oh yeah, the light burns brighter as the locomotive speeds up, dimmer as you slow down is the situation...

  2. green_elite_cab

    green_elite_cab Keep It Moving!

    you can get some low draw lights, or you can switch to DCC. that will solve the problem.
  3. jim currie

    jim currie Active Member

    there was a article some time back about using a recharble battery to keep loco light lit
  4. pgandw

    pgandw Active Member


    I assume you are using DC because most DCC decoders provided a constant voltage source for lights.

    In DC, there are only 3 ways to provide lights without the locomotive moving:

    1) battery power for the lights. Space for batteries is a real concern, and most people would want a battery charging circuit from track power to avoid frequent battery changeouts - means rechargeable batteries. Then you need some way to turn lights on/off. A magnetic reed contact inside the locomotive that can be thrown by waving a magnet is probably the best bet. It's been done, but it's not easy in HO and smaller.

    2) A throw back to the '50s and '60s - high frequency lighting. Superimposes a high frequency AC on the rails to provide power for lights. Requires DC blocking capacitors in lighting circuits, and choke coils in motor circuits. Difficult to regulate power and frequency for a larger layout. Can cause interference problems because rails and wiring can serve as an effective antenna. I've seen circuits but never seen high freq lighting actually used except on display layouts.

    3) Most common until the coming of DCC was constant intensity lighting. Available commercially or roll your own. Works by setting up a 1.4 volt drop across 2 banks of 2 diodes (1 bank for each polarity). Uses 1.5 volt light bulbs. Very compact. Uses the first 1.4 volts of track voltage to light the lights. After the 1.4 volts is going to lights, then voltage goes to motor. Not a great idea to leave your motor standing still with 1-1.4 volts going through without moving but most motors will take it. Bulbs stay the same brightness while engine is running. Reduces top voltage available to motor by 1.4 volts - for most engines this is pretty desirable!

    LEDs can be used instead of light bulbs, but require a different type of lighting circuit. They use less current, run MUCH cooler, and last forever if not subject to overvoltage/over current. If run off 12 volts or similar, each LED usually requires a 1K resistor to limit current and voltage.

    Hope this helps.
  5. 91rioja

    91rioja Member

  6. Wyndigo

    Wyndigo New Member

    Thanks for all of the replys, gonna look at the links and look into all of the advice.
    DCC isnt really an option (cost & planning a move later in the year)
    :wave: see ya'll later

  7. farnham

    farnham New Member

    Tell me more.

    Fred, Yes I'm favoring fairly primitive railroading, so constant lighting would be about as far as I would go. Thanks for clearing this up. Just a few remarks if I may:

    Are you sure the one you describe with two diodes is the only one? It seems to me I built one or two of them and there was a transistor or something?

    Also-- and here my ignorance of electronics shows-- if there is current going through the motor, why doesn't it move?

    Thanks . . . :cool:

  8. lester perry

    lester perry Active Member

    There is a simpler way I use it all the time. Go to radio shack get a bridge rectifier. It will have 4 wires bend the one with + next to it and one opposite it across each other and solder cut off remaining wire at solder. The other 2 bend out , cut one lead to motor and solder this in line. Between power source (wheels ) and motor. The use a 1.5 volt bulb put one lead on each side of the rectifier. The light will be bright and constant.
    wheel--------lead wire-<rectifier>-lead wire-------motor
  9. pgandw

    pgandw Active Member

    I can't think of any reason for the complexity of a transistor in a constant intensity lighting circuit. Transistors are regularly included in capacitive discharge systems to speed charging while restricting current to the switch machine to just the capacitor charge. Transistors are also used extensively to control voltage in DC throttles.

    The motor takes a certain amount of current to start turning. It actually draws more current just before starting to rotate than once it starts rotating. This is called the starting stall current, and is another reason rheostat throttles don't provide smooth starts and slow speed running. As soon as the motor starts to rotate, its current draw drops, and the voltage drop in the rheostat drops accordingly. This increases voltage to the motor at the very moment you want to hold it steady or even reduce it slightly. Thus, you have a "jack-rabbit" start with a rheostat throttle.

    If the voltage/current is insufficient to start the motor rotating it just sits there with a low current passing through it. This will cause some heat build-up, depending on how much current. In most cases of modern low current motors, it should not be enough to do any harm. Older open frame motors, although drawing considerably more current, also have considerably more heat dissapation capability. Heat is proportional to the current times the voltage or current squared times resistance.

    yours in powering up
  10. farnham

    farnham New Member

    Thanks Lester and Fred!

    Does DC stand for digital control and DCC for digital cab control-- I am only guessing! And in DCC is the handling of reversing loops any different than in plain cab control? Correct me if I'm using the wrong words . . . I'm not planning to have any reversing loops but I'm just curious about that.

    Also always was curious, what do different DC throttles do? Do they slow the change in voltage through capacitors, etc.? Do some of them actually monitor the speed of the motor through the pulses of the commutator or some other way of sensing speed? Particularly I'd like to know can they prevent trains from speeding up on downgrades?

    More years ago than I care to mention I was attending (not a member of) the Empire club in Long Island City and they had Variacs, variable transformers-- what do you think of them?

    Fred, what do you think of Lester's solution? Are they actually similar? Which would be less expensive?

    In any case, I am thinking of building a very long narrow shelf railroad. Such a long railroad might involve separate cabs at the ends and at major locations, 2 to 5 cabs, and each would be the sole power for its own section. Would this run into problems with crossing gaps, circuit breakers? Would it be possible to run a train continuously over different power packs? Or what about a central power source connected to the common rail and each local cab somehow? I am looking forward to having a diagram made so I can show it to you guys and others.

    I am also hoping to build the pike in sections with connectors between them so they can be swapped or taken off the wall to work on. Know any good connectors?


  11. MasonJar

    MasonJar It's not rocket surgery

    DC refers to Direct Current ("old" powerpack way of running trains by controlling the power supplied to the rails)

    DCC = Digital Command Control. The track is always at full power, and a little "computer" inside the locomotive controls how much power the electric motor gets. Operates much like a computer network.

    Check out for an explanation of DCC.

  12. pgandw

    pgandw Active Member

    DC stands for "Direct Current" and is the standard way of controlling scale electric trains since the 1940s. It uses a variable voltage 0-12 (sometimes less for N and Z) volts DC on the rails to run the electric motors. The 3 rail O guys and Marklin HO stud system still use 0-16 volts AC (alternating current) for their motors - a hangover from per-WW2 - but the NMRA standard is 12 volts DC.

    DC control used to be done (and still is in cheap train set power packs) using a variable resistor called a rheostat in one of the leads to the track. The higher the resistance setting of the rheostat, the more the voltage dropped in the rheostast, and the less available for the train. Because the voltage dropped in the rheostat at a given setting depends on the current drawn by the train motor, this is not a good way to control modern low current motors, and especially a mix of high current and low current motors. More modern power packs such as MRC Tech 2, 3, and 4 have what are called transistor throttles. These throttles directly control the voltage to the track rails through the use of transistors and other electronics. Some of the more sophisticated throttles can use feedback to sense what is happening with current draws and what is called back emf and adjust the voltage to prevent speeding up going down hill (or slowing down going up hill). There used to be arguments in the hobby magazines about whether such features were desirable or not. Many operators insisted it was their job as engineer to adjust the throttle for the grades, not the electronics, just as on the protoype. Same is true with momentum settings which prevented the locomotive from accelerating or stopping quickly. Use of electronic momentum is still controversial today, as is "cruise control". Some like it, some don't.

    Variacs control the house voltage going to the power pack, and can eliminate the problems with rheostats. However, they are not particularly safe in the hands of the ignorant when short circuits take place. More importantly, compatibility with transistor throttles is an open question - most modern electronics do not take kindly to having the input voltage vary beyond a small range.

    The consensus best way to run DC control is to have one throttle for each locomotive being run simultaneously. The track is broken up into electrical blocks with toggle switches to select which throttle controls a particular block. Wiring and switches are normally set up to interlock so that only one throttle can be selected for a given block. By flipping the block toggles to the appropriate throttle as the train proceeds on the track, the same throttle is used for the same train throughout its journey. If you are only operating one engine on the layout, you set all the blocks to one throttle.

    DCC is a Digital Command Control System. Each locomotive carries a computer chip with its own address called a decoder. The command station sends out commands to particular decoders based on the address set in the throttle. The command station sends both power and commands through the track. The decoder reads the commands, and feeds the appropriate amount of power to the motor in the locomotive. The newer decoders can read back emf from the motor to provide cruise control and momentum functions as desired and preset by the CVs. Decoders also have a table of user settable configuration values, or CVs, that allow you to custom tailor the locomotive's performance curves to your taste.

    Because DCC can address each locomotive independently on the same track, there is no need for block toggles. You still want a separate throttle for each locomotive being operated simultaneously, otherwise you better have nimble fingers and an even quicker mind to jump back and forth between 2 engines with a single throttle.

    Almost everybody I know of uses automatic reversers in DCC. After all, with all the $$ invested in DCC, what's a few more. You simply isolate your reversing loop or section, wire up the automatic reverser and let it do its thing. No short circuits to shut down your command station.

    There are automatic reversers for DC, but they are generally not used. You need 2 direction control switches downstream of the power pack - one for the reversing section, and one for the rest of the track (more if you have multiple reversing sections). The reversing section direction controller has to be aligned correctly for the train to enter the reversing section. Then, while the train is totally within the reversing section, the main direction switch is flipped so the train can exit the reversing section in the opposite direction.

    Lighting - the full wave or bridge rectifier Lester recommends is the functional equivalent in a single package of the 4 diodes I mentioned.

    Module connectors: most of the module standards specify the connectors to be used between modules. You might check those out. If you want to roll your own, the most durable I know of for up to 7 wires is the RV trailer connection plugs. They are bulky, available in both plastic and metal, but the most durable and readily available way I know of outside of high cost aviation plugs and receptacles, to repeatedly connect and disconnect wiring across a joint.

    Long post - I hope I answered about all of your questions.
  13. farnham

    farnham New Member

    Just about what I wanted to know.

    Thanks again Fred. Not too much and not too little-- you are definitely on my frequency. Are you guys engineers or what?

    I am thinking about a shelf railroad more than fifty feet long, operated at times by children with their own trains. I am wondering if we could have one end on one power pack and the other end on the other, and still get trains across? Provided of course that both were set to the correct polarity. Would the train then short-circuit or would it continue? That is my basic question, although at this point I probably should be trying to learn more about all of the possibilities.

    I only had two railroads as an adult, the second had a reversing loop. It used cab control as it was then called with DPDTCO switches that of course would not allow two cabs on the same section, since there was only one set of switches. But how could the same thing be arranged with two cabs set far apart, or with more than two cabs? I believe you that it can be done, but I can't quite conceive of how. I begin to see-- could they work the same way as those switches down a hallway that allow turning on the light from one end and then turning it off from the other end? Called three-way switches? Why three-way? Anyway three-way switches if that's what they're called are one thing that always confounds me.

    Aren't there two types of variable resistors, one with two poles and one with three, one called a rheostat and the other a potentiometer? What is the purpose of that?

    I would want to prevent my trains from speeding up downhill but not from slowing down uphill-- more prototypical? What do you do with your trains?

    I miss the way Lionels, etc. would glide when they stopped (not a good idea on steep grades I guess! but in those days I didn't have grades), which meant one could also turn the wheels and the valve gear by hand-- very satisfying! Many people who have had toy trains don't understand that the engines these days won't do that. I'd at least like to see an HO engine or engines that acted that way when they stopped, to see if it was convincing.

    But more practically, I'd like my engines to be able to crawl as slowly as possible , and also have speed limiters so children couldn't run them too fast.

    In any case, the way you describe the characteristics of the rheostat, those jackrabbit starts and stops could not really be stopped at all by the engineer without some kind of circuitry.

    I'm not considering variacs for myself of course. Especially now that you reveal that they vary the house power, I think any device that does that has no place in a model railroad or any consumer appliance.

    Can you say in layman's language how an automatic reversing loop controller in DCC could work? Obviously a manual one would work also.

    Which would cost less, bridge rectifier or four diodes? I definitely want to make as many constant lighting circuits as I can. I believe I tried to actually make a battery type, not rechargeable, with a switch connected to the coupler bar-- no thanks!

    Thanks for the tip about connectors-- I'm thinking I would need 30-50 wires? What about those plugs that go to CD drives in computers? Best wishes,

  14. pgandw

    pgandw Active Member

    If you are really talking about a 50ft long shelf railroad with multiple operators, walk-around control is a must. If there are more than 2 operators at a time, you are pretty much past the "break-even" point for DCC. The extra wiring, switches, multiple control panels, and operating headaches of cab control in your situation make DCC a natural.

    There is an HO modular system called "Free-mo" that appears to fit in quite well with your stated plans. Here is a link to their forum,, and I believe their module standards are in the files section. At least there are links to their standards page. Free-mo uses Digitrax DCC as standard, and they have the wiring and connections all included in their standards. All the engineering is already thought through for you. The added benefit is that there is probably a Free-mo group in your area, with whom you could team to display some of your modules on occasion. Even though I am not a Free-mo follower personally, I lurk on their forum to steal ideas shamelessly.

    My personal preference is for integrated (baseboard, backdrop, upper functional bookshelf with lighting under) bookshelf layout sections that can be wall mounted in the living room. But because I'm different, I get to engineer my way through the anticipated and unanticipated problems myself - an aspect of the hobby I enjoy.

    Another advantage of DCC is that you can program the performance curves of the locomotive into the decoder - setting top, minimum, and all the in between speeds. You can preset momentum effects. Momentum, when used, will simulate the coasting effect electronically. To do this easily, you need a DCC system with a computer interface, and a computer running JMRI (free software). Momentum and voltage presests (top and low) can be done with fancier throttles in straight DC, but would have to be adjusted when you switched locomotives.

    The DCC auto-reversers sense the instantaneous polarity mismatch as the metal wheels of the train cross into/out of the isolated reversing section, and reverse the polarity of the reversing section before the system circuit breakers can trip. Apparently, the solid state units from Tony's are really sweet. You can do it manually - in DCC you swap the polarity of the reversing section while the train is in it. In DC, you change the polarity of the rest of the layout while the train is in the reversing section.

    Couldn't tell you about actual or relative prices of electronic components - I haven't bought any in a while. At Radio Shark - if they still stock parts - diodes and resistors should come around 4 to 8 in a package for a few bucks (rip off price). Full wave rectifiers are a couple of bucks each (again Radio Shark's rip off pricing). But Radio Shark is getting out of stocking parts; you may have to order on-line. Out West, we still have Frey's Electronics which has some parts at reasonable prices.

    A potentiometer (pot) and rheostat are the same thing, with the rheostat generally considered to be a higher power device. Both almost always have 3 connections - one at each end of the resistor, and one for the sliding wiper. In non-transistor circuits, usually only 2 connections are used to get the variable resistance. Pots in transistor amplifier or op amp circuits often use all 3 connections in a voltage divider configuration to set the voltage going to the transistor base or control gain of the op amp.

    I empathize with you about the old Lionel stuff being able to be pushed by hand. Even at the age of 7, I enjoyed pushing it myself as much as I did controlling it with a transformer. It is the price the scale modeler pays for slow speed performance. To get the needed gear reduction single thread worms are used. This gear configuration cannot be reverse driven, which is why most HO cannot be pushed. A mulitple thread worm can be reverse driven, as can spur and helical gears. Lionel used multiple thread worms in some of its early large steamers, but the gear reduction is directly related to the number of threads on the worm. A single thread worm with a 36 tooth worm gear has a 36:1 reduction. A triple-threaded worm with the same worm gear has a 12:1 reduction. But kids used to race Lionel engines - you don't see that in HO. Because of the inability to be reverse-driven, HO locomotives don't speed up as much going downhill as Lionel, especially with a transistor throttle or DCC. They may "buck" if there is play in the gear mechanism or motor shaft and the train is pushing them from behind.
  15. farnham

    farnham New Member



    Thanks so much for yr attention to detail. Are you and the other people on this forum some kind of engineers who walk around in white coats? I am impressed with yr knowledge and understanding.

    As for DCC-- gaaa! Chips inside the engines!!! And I think DCC might hold a risk of children crashing engines/ trains into each other-- and DC might have better potential for rescue by isolating/ turning off sections. Correct me if I'm wrong on this or anything!

    Of course if I actually operated DCC myself I might think differently! Even catch some of the enthusiasm that surely others have for it??

    How's this: One power pack/ controller/ section for the entire main line with a walkaround DC controller-- I assume there are/ were such things? Each of the two-to-five local facilities (yards, stations, industries) has its own power pack connected only to it, with a small section of the main line attached with a DPDTCO toggle so that engines/ trains can be interchanged. Each facility has its own power pack (walkaround or stationary) and operator, or the same power pack (not a walkaround type) can be plugged into different facilities. One operator can run trains on the main line, continuously or to stop them where needed, then move to the local power packs for switching. I'm assuming there are/were such controllers for DC-- it seems I used to read about them touting that you could leave the train running while you disconnect and move to another location-- maybe even two or more on the same section? I don't see why not.

    So the whole thing would work without more than two power packs being attached to any segment of track. I do hope the walkaround units I describe exist or can be built, evidently some kind of electronic system but I'm hoping that it is one that has nothing to do with DCC.

    Getting on to construction . . . soooooo! You are a shelf railroader too! That thought always had an allure for me (carrying coffee cups or at least sugar cubes between different parts of the house) and I presume the sections would be easier to move without legs. I am most, most intrigued with your "integrated (baseboard, backdrop, upper functional bookshelf with lighting under) bookshelf layout section," which seems very much the way that I should go, except that instead of a bookshelf above the baseboard the backdrop or painted scenery could continue upwards for some distance-- I don't know how this would work in terms of perspective, roads or rivers going under or over the tracks and then continuing into the far distance?

    I'm thinking about a shelf with track supports 4-8?? inches above it to allow for rivers, valleys and other dips in the scenery. And yes an integrated baseboard and backdrop with lighting included. I would be very grateful if you had plans and/or pictures. For a start, what kind of scenery did you have and how did you bulid it? In particular, what kind of brackets did you use or build? I have a 1 inch thick molding just above the shelf, so I'm thinking the backdrop would best be supported/ steadied by the risers or lintels of the trackwork above the shelf . . . :wave:

    Thinking about trains,

  16. pgandw

    pgandw Active Member


    With the coming of DCC, getting sophisticated DC systems has become much more difficult. There are still some available commercially, and used ones might turn up on eBay. MRC used to make a hand-held walk-around, and I built a simple one myself. But finding one that allows you to disconnect with train running will be a little tougher find. Your cab control wiring plan is workable as described, and I have seen DC throttle circuits in model rr magazines (generally in '70s and '80s) that do exactly what you describe. Also, Peter Thorne's books on electronic projects for model rr probably has some too. Online resources I know of are and Not saying that these sites have the right circuit for you, though.

    There are 2 common ways to get the track height above frame base you describe - layers of extruded foam, and conventional riser and cleat form the frame to the roadbed. I haven't built a shelf layout yet (only island-style and table types), so I can't really tell you which is "better". With kids operating, I would lean toward the foam, which you carve away for below track scenery. This gives a resting place for derailed equipment that is not the floor from the get go. The typical riser, cleat, and raodbed system has open spaces between tracks until the scenery shell is put in. Foam will probably give significantly lighter layout sections, but will be more difficult to generate realistic and consistent rugged terrain. Can be done with foam, but takes more effort. Foam is easier to place buildings and structures on the layout with because of its natural flatness. Trees can be poked into foam, you have to drill holes in a plaster shell.

    Suggestion: mount and paint the backdrop before you install track and scenery.

    I think you have enough to get started with. Read mr press articles and magazines, join the Yahoo Layout Construction Group, and have fun.

    my ideas, your choices
  17. Canopus

    Canopus Member

    On an old layout, I solved this by using a battery that was constantly recharged by the power from the track whenever the loco was used, and the power from the battery fed the lighting. A small circuit between the power from the tracks and the battery helped even out the irregular power flow (changing loco speed etc.) thus preventing the batteries from fatigueing.

    Worked very well, only downside was having to occasionally replace batteries. Also, leaving the locos for a year then coming back to them only to discover the chassis to be caked in acid was a major setback to say the least. But the latter can be avoided and the former wasn't such a drag really.
  18. cidchase

    cidchase Active Member

    I saw that circuit in a model railrod electrical book for lighting cabeese and passenger cars, no reason it wouldn't work even better on a loco which already has pickups!! :D
    Sounds like a good idea! On DC layouts, the lights will stay on when the train stops at the station! :thumb:
  19. farnham

    farnham New Member

    Shelf railroads?


    "My personal preference is for integrated (baseboard, backdrop, upper functional bookshelf with lighting under) bookshelf layout sections that can be wall mounted in the living room." I thought this meant you built a shelf railroad-- I guess it means this is your opinion about what would be the best way?

    I'm thinking some of this discussion could go in a different thread, such as layout planning. Is there a way to transfer some or all of it? :)

  20. Canopus

    Canopus Member

    Precisely, the power to the lights remains constant, and the battery recharges itself whenever the train moves.

    However, before you go running off into your workroom to build yourself one of these, let me just suggest to you to build in an ON OFF SWITCH between the battery and the lights. The first loco I built with this circuit, I forgot to add one! I quickly realised once I'd finished using it that the light would keep on burning until I removed the battery. Taking the shell off a loco every time you finish using it is a major pain in the ass let me tell you, so save yourself a bit of time by putting in that switch, and having it poke out the bottom of the fuel tank, so that you can just pick up the loco, turn it up side down and switch the light off.

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