If you can't afford to lose motor voltage so you can maintain speed compatibility with other locos, you'll have to take another route. There are several I can think of, but all have problems. Adapting the circuits I have described above to use a resistor instead of the motor in series with the lights becomes very tricky. The problem with this is that the resistor will need to be sized for the maximum number of lamps, and it will have to dissipate quite a bit of heat, and you won't get constant brightness lighting over anything like the full 12V range. Another solution could be the voltage regulator route which will give you constant brightness from a fairly low voltage, but it gets tricky when you introduce directional lights. It would probably require 3 or 4 regulators, or perhaps 1 plus additional transistors and rectifiers, so space might be an issue as well. Unless you are fairly comfortable with electronic circuits I'd avoid it. If you really want to give it a go I'll try and work up a circuit for you, but it might take a little time. The simplest is probably the 'standard' method which is to run the lights off the track supply and use one resistor for each lamp. For 1.5V/0.015A bulbs in a nominal 12V circuit you need a 700ohm resistor in series (in theory). You could use a 680, which is the closest standard value, or a 750. Where a diode is used for direction control the resistor should be less, about 650 Ohms, so you could use a 620 or 680. In both cases lamps will be a tad dimmer but last longer with the higher value. With this method your lamps will only be bright at high speed, progressively dimmer at lower speeds. It comes back to philosophy again - which compromise do you want to take? It sounds to me as though you (John) aren't too bothered about constant intensity lights, so you should probably go with that last suggestion. If you want constant intensity you either have to lose a bit of compatibility with other engines, or convert all of them (you don't have to fit lights, just the diodes in series with the motor), or use a more complicated bunch of circuits. 1N4000 is the name of the series of diodes; the actual devices are 1N4001, 4002, 4003, etc. The higher numbers have a higher reverse voltage rating, 4001 is 50V, 4002 is 100V I think, etc. They are made by many manufacturers and usually come as a cylindrical black plastic device, although I have had glass ones which are smaller. I had a quick look in Radio Shack website and only saw the 1N4003 (which surprised me). I did think of a limit to the number of lamps you can have with System 1 or 2 above - the lamp current can't be more than the motor is drawing Probably not a problem with a twin motor monster, but maybe a limit with more normal offerings. (If the limit is exceeded is just means the lamps will be a bit dimmer until the motor draws more power; no harm will happen.) For anyone interested here is the circuit P2k used in my switcher. This is from an older unit. I just had a quick look at a couple of newer ones (with DCC plugs). They have different boards and one has surface mount components. I didn't trace the circuits out, but both have 8 diodes on them, so I expect the actual circuit is the same.
Mike, The simplest is probably the 'standard' method which is to run the lights off the track supply and use one resistor for each lamp. For 1.5V/0.015A bulbs in a nominal 12V circuit you need a 700ohm resistor in series (in theory). You could use a 680, which is the closest standard value, or a 750. Where a diode is used for direction control the resistor should be less, about 650 Ohms, so you could use a 620 or 680. In both cases lamps will be a tad dimmer but last longer with the higher value. With this method your lamps will only be bright at high speed, progressively dimmer at lower speeds. It comes back to philosophy again - which compromise do you want to take? It sounds to me as though you (John) aren't too bothered about constant intensity lights, so you should probably go with that last suggestion. If you want constant intensity you either have to lose a bit of compatibility with other engines, or convert all of them (you don't have to fit lights, just the diodes in series with the motor), or use a more complicated bunch of circuits. I'm not to much looking for constant brightness.. I'm looking for the controls of being dirrectional, an the bulbs being compatable with 12 VDC for the 1.5 VDC bulbs. I'm not worried about the brightness! I just have to make the bulbs compatable with 12 VDC and still be controled by a diode for making them work in directional flow of electric. So that the headlights only burn in forwards, the reverse lights only burn in reverse, an the ditch lights burn in forwards, an the marker lights get no diodes being all for burn in all directions at the same time. And possibly a cab interior light as well..... I'm not to worried how bright they are or anything like that I just need to cut the 12VDC to 1.5 per bulb, an then make them that the bulbs will be directionally controled with a diode....
This is my suggested solution John. You should test out the resistor values with your actual train power supply before comitting to them - you may find the lamps too bright or dim for your liking. But don't push the bulbs much over 1.5V or you'll be changing them too often. You could always increase the resistance for (eg) the marker lights if they don't need to be as bright (and if they are red lensed they won't need to be). This would increase bulb life and reduce heat as well. The dissipation of the resistors here is about 0.18W at 12V supply, so 1/4W units should be fine. 1/2W resistors would run a little cooler, but will be bigger and so harder to fit in. A 1/4W with a millimetre airspace round it is probably preferable to a 1/2W in contact with a plastic shell. As you are building this yourself I imagine you will have 'real' grilles (with holes in) so that will help with heat removal. Having lots of resistors may be a nuisance space-wise, but it does mean you can spread them - and the heat they give off - around the bodyshell. One big one would be much harder to deal with, as well as having other problems.
Mike, I'm making the center flywheel with "fins" in it to suck or pull air into the shell from the bottom, an then will have open grills so... BUT with smaller resistors an diodes spread out across the metal frame well.. would be like a heat sink almost so.. I won't have them near the plastic shell so. I'll have them on the frame of the loco which is all cast metal an all... So, heat shouldn't be to much of a problem. I'm going to print out your diagram an take it with me for a "parts list" and then use it as a builders diagram.... Yeah, this will work, I wasn't looking for constant brightness.. as I don't like my headlights extrememly bright (helps save the bulbs from burning out) but I knew I had to lower the voltage from 12 VDC to 1.5 VDC.... And also be directionally control by loco direction.
Hey John, I meant to put this up before as an alternative, but stuff happened and I forgot This will use less resistors by putting some bulbs in series if space or heat is a problem. Should be OK in theory, but these are the possible gotcha's I know of: 1/ Only put bulbs that are near each other in series - otherwise you can end up with some awkward wiring. 2/ If one bulb fails both will go out. (But the 'unfailed' one will still be OK, so you only have to change the one)(but you have to find out which). 3/ Bulb characteristics do vary, so you may find that a pair are not the same brightness. Depends on the quality of the bulbs. (This is less likely with 1-resistor-1-bulb, and in that case you can always alter one of the resistors to correct it.) If you want to put more bulbs in series you need to reduce the resistor by 100 Ohms per bulb (for these 15mA ones) but the problems above may become more acute. (8 bulbs would not need any resistor at all.) One other suggestion - when you bench test, fit the bulbs into holes drilled in some scrap plastic sheet or thin wood to simulate being mounted on the engine. They can look quite different when shrouded to dangling loose. OK, I'm gonna shut up now
Mike, I like the one resistor to one bulb thought, its a simpler design an even a better design! Even tho, it has more components! With the body an inside body size of the SD-90MAC, customized into a SD-80MAC, space shouldn't be a problem! And if need be, I'll channel out a grove in the frame, to put the resistors an run more thin wire to where it needs to be to eliminate the resistors everywhere inside... Then, that will make the frame act as a heat sink! I'll just have to be carefull, where I make the channels for the resistors being they can't hold the loco body up off the frame, when mounted.... As for "testing" the bulbs once together..... I'll use the actual loco shell for this, being everything is made onto the loco an waiting.... BUT I won't mount then rigid to the body, being they will slip right in place an right out of place etc for maintenance.... Once done, a little bit of "stick-it" temporary adhesive, will hold the bulbs in place, with no trouble, I don't want to use glue or the likes as to making maintenance difficult.....
Hello John, I'm a little late to the discussion, but I have a question for you. what kind of motor are you using for your custom-made locomotive? This is key. I tried experimenting with diode lighting circuits a few years ago (before the kid was born) and found out that can motors and diode lighting circuits have a big limitation that must be dealt with. If you are using a can motor the motor draw is down in the milliamps and you won't get your lighting package to work unless your run your locomotive a full speed or unless you include some resistors in series with the motor to create a large enough. The old six-diode reversible lighting circuit requires a motor with a fairly high draw in order to get the lights on. You can crack the throttle and the lights will come on and the train not move. And as the throttle speed increases the lights remain on at constant voltage. If you have an old Athearn locomotive from the 1980s, you could use the diode circuit without resistors because the motor draw tended to be high. Another option is the voltage regulator circuit. But typically this circuit will not work with the train stopped. You need the train at least creeping. Both types of circuits have their advantages and disadvantages. The voltage regulator circuit is not connected to the motor and just operates off track power. The diode circuit is connected to the motor and you need to balance the circuit with it. One caveat, this post is based on my experiments from the 1990s, so I hope I'm not too out of date. I would welcome any comments from others to help me get updated. Thanks, Clifton Linton
Clifton, Well I'm currently using the Athearn High output motors! the type Athearn use in their C44-9W's an the AC44CW.... Which will work fine with the diode diagram. HOWEVER, the new can motors are very good with voltage regulation. I want to later one, upgrade this same loco with A-Line dual can motors.... Without Flywheels as I'll have to add my own flywheels to these 2 motors, being I want to run 3 flywheels. So, with this said I shouldn't have no trouble with any of it, as I have one loco already with an A-Line can motor, with the diode systen in it already. But it has 12 volt DC light bulbs not 1.5 volt DC bulbs like this one will. This is why I had to do extensive research an all to see how exactly to make the 1.5 volt DC bulbs run from 12 volt DC without blowing them when the power is turned on an then have 9 to 10 bulbs shot.....I wanted to make sure it was right before hand to save me that loss, those bulbs aren't cheap! Specially ones from Miniatronics....
Mike, As you done the diagrams for me, I have a question, Say I were to use 4 bulbs in a different locomotive, say a Athearn SD-40-2, with one motor, an wanted 2 bulbs for the headlight (as one bulb per headlight lens). being 1.5 VDC 15mA. How would I go about doing this with the resistors? Or would it be the same as the one resistor to one bulb diagram, be less bulbs an less resistors? Chance you can help me with this one as well ? I'm trying to get to know the electronics on this then, I'll be able to do all this work myself!
John, if you mean you are just having two bulbs for forward headlights and two more for reverse, then it will be as you say - "one resistor to one bulb diagram, but less bulbs and resistors". Specifically, in the diagram with my 8 Sept post, ignore the entire "Always" portion and the "Ditch" bulbs - that will just leave the four headlamps. With this system the lamps are all pretty much straight across the rails (excepting the direction diodes), so you can add or remove individual bulb/resistor pairs without affecting any other lights. Clifton highlighted the limit I mentioned at the end of my 7 Sept post. (They haven't changed the laws of physics much lately, so I think those experiments will still hold good. ) This limit does not apply to the system you are using, John, as the motor(s) are not involved in the lighting at all. (It is just shown on the diagram for completeness and so you can identify how the lights may be wired in.) .... Going back to the constant brightness circuits, Clifton's post got me thinking and I then remembered that MR give speed/voltage/current information when they review locos. I pulled out a few back issues and there certainly could be problems using the constant brightness circuits with some of these. All I looked at pulled at least 20mA (0.02A) at low speed so should work with one lamp always on, or two if both were (opposite) directional lights. Most other engines would probably handle 4 or more lamps, though you might not get full brightness at very low speeds. You'd have to experiment a bit. One of the down sides of can or other low current motors . Clifton also mentioned "Another option is the voltage regulator circuit. But typically this circuit will not work with the train stopped. You need the train at least creeping." There is a fix for this - add diodes in series with the motor (as for the diode constant lighting, but without the bulbs) until the starting voltage of the motor/loco is higher than whatever the voltage regulator needs to get the lights on. But (of course there's a 'but' ) this will take quite a bit of speed off the top end, and if multi-heading would almost certainly cause load sharing problems unless you do all the locos involved. [ 01. October 2003, 19:07: Message edited by: Mike Sheridan ]
Mike, I just wanted to know if the diagram for one bulb to one resistor could be lowered to as you said 4 bulbs without changing any of the resistor values. so, inother words, this diagram... I can subtract lights to resistors from the amount shown on it to like you said 4 bulbs to 4 resistors (one resistor to one bulb) without changing the resistor values. Correct? But this diagram is the one I'm using in my custom SD-80MAC, I just have a few other loco's that I want to put lights in just like this, just not with all the intricate electronics... Just 4 bulbs, with 4 resistors for 1.5 VDC, 15mA, bulbs... EDIT: I need to learn how to spell, an also need to mention I reposted this image that Mike had posted first so, that Mike knows what diagram I'm talking about. [ 02. October 2003, 00:32: Message edited by: 7600EM_1 ]
I think you've got it John, but here is a kitbashed version of the diagram just to be sure Incidentally, with all these systems you may have to change the direction of the diodes to get the correct operation. In theory you have a 50/50 chance of getting it right first time, but Murphy's Law takes precedence over theories . Don't change the motor wires over, please ...
Mike, How I know about turning the diodes around! I think I've only gotten the diode in the right possition a few times (And I've done MANY dirrectional lighting jobs)! I know its like a hit or miss thing being the polarity + or - is a factor an its hard to judge it right. As for the motor wires, This is why I do one side at a time, unless the wires are color coded an I know what color went where.... But then thats on a complete dis-assembly tho, when doing this, I seldomly remove the motor wires! Unless like I have said, its a complete dis-assembly! THANKS again for the diagram for the 4 bulb system! [ 04. October 2003, 12:36: Message edited by: 7600EM_1 ]
