Converting Mth PS units to forward only

I would wire the powered unit this way. Better than series wiring IMO

 Click to enlarge

The voltage dropper clamps 4.2 volts pulsed DC whenever current is pulled through to the motor. The motor will receive about 5 volts less than track power,so the unit can be stalled at 5 volts and the lights will be left on at full intensity. Resistors are shown as half watt but 1/4 watt is OK. These are minimum values in ohms. The marker LEDs in series are + to -. Polarity should be paid attention to.

The bridge rectifier should be 6 amp or more.

Dale H

Thanks but, In regards to subways I find that if hooked up in parallel that the lead truck lifts up and pulls a wheelie and is prone to derail when starting off near or on a curve while pulling more then three coaches.

 Also the other coaches on the line do not receive enough power to light the bulbs up adequately since little power is needed to operate the motors that way.

 So then if I was to hook it up the way mentioned with the motors in a series instead, since I only use 75 &100 watt transformers, with the 5v less power, I would have to max out the power on the transformer to operate which may not be enough power to pull five coaches.

So to update this post a bit. I started off with the motors hooked up in parallel and I found that the unit used little power, ran fast and "all " coach lights were to dim. Also the lead truck would pull up and be prone to derail on or near a curve when starting off while pulling more than three coaches.

 So I now have it hooked up in sequance which is the way that they come from the factory and it operates the same as it should. 

 My issues have been with the lights. While using the mth bulbs already installed I hooked up a 5v regulator and a 25v cap. But for some reason it will not operate the four bulbs that I need, 2headlight & 2markers. all white incandescent bulbs. They will start up as they should but quickly dim and not regain their regulated voltage until I slow down and come to a near stop.

 Yesterday I tried just using two of the four and the two worked as they should.

 So I would like to know how to solve this issue thus far. Why do two work and four do not ?

Now on another note, I did order some 1.8mm soft white  12/18v led bulbs from China

which will take weeks to arrive.

So ultimately I would like to know how to correct my current issue thus far.  Then when the led's arrive how should I go about installing them without to much of a drastic change from what I have set up already.

Again I operate in conventional using mth 75 & 100 transformers

Thanks to all that reply.

The problem you describe relates to series wiring,not parallel wiring. In series wiring if you stall one truck,the other will speed up,pushing a stalled truck with traction tires. In parallel wiring both motors receive the same voltage. If you stall one truck the other spins about the same rate of speed. The stalled truck still has equal voltage.

The diode dropper gives 4 volts less to the motor than it otherwise would have from track power. So the lights would have 4 more volts at a given speed.

At 18 volts throttle with series wiring each motor would get 9 volts. On a sharp curve load would be uneven and voltage would not distribute evenly.

At 18 volts throttle with the parallel wiring and voltage dropper, each motor would get 13 volts even counting the voltage drop of the bridge.

Thus the parallel wiring has more pulling power potential.

If the LED are hooked up as described they will burn at constant brightness from 6 to 18 volts on the throttle.

At 5 to 6 volts the motor would stall,but the lights would stay on since they still have 5 volts. The engine lights are wired through the dropper which clamps the voltage. The lighted cars would receive 5 volts from the track. The LEDs in parallel would burn at full brightness from 5 volts up.  I think you said you wanted be able to stop the subway and leave on the lights. This circuit will accomplish that. At low voltage the motor would just buzz a bit.

The transformer wattage is sufficient. 90 watts will run a 2 motored unit and 5 cars with light bulbs or LEDs. If you used a 180 watt transformer nothing would improve.

 The diode string uses some power but not enough to affect running. Power used by the diodes would be about 4 times the motor amperage. Maybe 8 to 10 watts if the motors pulled 2 amps. As long as they can shed the heat this is not a problem.  The LEDs in all the cars might use 8 watts. The 2 motors maybe 20-40 watts.

I would not use the 25 volt capacitor. Just because you have one does not mean it is appropriate for the job. I may eventually explode and make a mess.  Use at least 35 volts. A 470 uf 35 volt cap maybe costs 15 cents, less in quantity.

Not sure I will change your mind on this point but I tried.

Dale H

Assuming the regulator is hooked up properly 4 bulbs may be over driving it past 1 amp. If the chip overheats it shuts off. At higher voltages the resistance of the regulator increases and it generates more heat.

At 18 volts throttle the regulator will consume about 2.5 times the wattage of the bulbs. So if 4, 6 volt bulbs consume 8 watts the regulator would consume 20 watts and one car would use 28 watts.. Even with a heat sink that is a lot of heat to get rid of. Also it is very wasteful of power. The circuit is not practical with light bulbs. 6 LEDs however would use only about  .6 watts,so the regulator would only have to shed about 1.5 watts. The whole car would use 2 watts,less at lower throttle settings. You can get by without a heat sink,just keep the regulator away from plastic parts and allow it to breath.  The low power consumption of LEDs makes the constant voltage lighting practical in passenger cars.

 The bulbs can be tapped off the diode string just like the LEDs in the last diagram I posted except no resistor. You don't need a regulator in the engine if you use the diode string.

White LEDs are generally 3.2 volts. What you ordered from China are prewired LEDs with a resistor in series to it,sized I guess for 18 volts. Input should be DC as it probably does not have a rectifier in it. 

Hi, thanks that was very helpful and I have a better understanding of the things that I have done so far.

So inregards to my incandescent light bulb issue. Before I had a chance to read your post today, last night I did discover that the regulator was extremely hot and got so very fast. Which was what was causing my issue. So today I purchased & put on a heat-sink. It is the better of the two offered at Radio Shack.

 Now the four lights work without issue. However like you mentioned even with it, it is still pretty hot. Not sure if it is within limits of the regulator tolerance or if it will cause an issue at some point as is, but it does seem to work. However though not the best option, I would like to know if it would be acceptable like this if I was to keep it as such.

    Also the same with that cap which I did have a 35 in my hand today but before bothering reinstalling that again I also thought that I would ask if it would also be acceptable with use of the 75 &100w transformers. I understand that if I used a larger transformer it would absolutely be needed & the next time I will install one regardless. But at this time would it be acceptable with those transformers ?

Thanks for your time..

Ok, all that aside. If I decide to install those LEDs when they arrive since it would help with that excessive heat /waste issue. If you don't mind could you let me know how to install such properly and as easy as possible with the set up that I have which is described below. 

 Idealy I would just like to hook up the four LEDs with their built in resistor in the same fashion that I have with the original mth bulbs which is after the circuit built with the regulator/cap.

 Or if needed, to disregard the reg/cap and wire it either after or before the diode ? Not exactly sure if it has to still be after the diode or it don't matter and I don't even need a diode any longer ?

Keep in mind at this time I do not have a diode string and will be using what I have which is AC to a rectifier, DC to the motors,,, a separate dc over to a terminal strip which is not grounded at the base. I have the DC to one post, diode over to another to reg/cap  then going around & avoiding the terminal ground, which then I have the lights to a positive post and one designated as a ground which has a return to the dc on the rectifier. That negative return post has the light ground cap & reg ground all attatched.

Thanks again... 

Also I would like to add that the next time I convert a unit I will do it the way that you described with the 6 diodes. However at this time since I already have changed this paticular coach set up twice already, I simple don't have the passion to redo it again. I just want four bulbs to burn correctly without any overheating issues.

Hook them up from the regulator output circuit just like the bulbs. They are polarity sensitive and will light one way and not the other. The built in resistor is for a value of 18 volts and you are applying 5 volts so they will not be very bright. If it is not satisfactory, cut out the resistor and splice in a 100 ohm or more,1/4 watt or more resistor in it's place. 

The 7805 should not need a heat sink with the 4 LEDs. At the very most it would use less than 2 watts.  Just leave some air around it and don't wedge it in an enclosed area. 

Dale H

Ok, thanks...

Is it also safe to assume that since the built in resistor on those led bulbs that I bought have a value of 18 volts.  I would also be able to disregard the regulator and just hook them up without it ? I don't mind them being variable since with the motors being hooked up in sequence they will have plenty of power to burn bright.

 So if was to do it that way I would be able to just hook it up off of the extra dc lead that I have going to the terminal strip and ground it back to the rectifier dc -... No longer needing any capacitor & diode ?

 Guessing by no longer using a regulator I would no longer have a need for a cap or diode.

  Is that correct ?

TY

Yes you can hook them directly to the track voltage but intensity will vary with track power. They may also flicker. A capacitor on on a DC circuit will eliminate flicker,however it would also increase the 18 volts pulsed from the track to 25 volts filtered which is more than the resistor is sized for.  Since they do not have a rectifier in them,it is best that they be hooked to DC power although they will work on AC,the reverse current is not good for them and only half of the sine wave will power them. That would make them even more prone to flickering.

 I misspoke in my last post,sorry,I meant to say the resistor was sized for 18 volts,not that it was 18 volts. It should be 750 ohm or more,half watt. If it is less than that it is not sized correctly. I would check it with a meter.  Without the regulator you don't need the cap. The voltage regulator circuit is composed of a bridge rectifier,,78XX regulator and capacitor. 

The motors are not hooked in "sequence",the correct terminology is series. Things are wired in series or in parallel or in more complicated circuits,combinations of the two. 

Dale H

Wow, this sounds complicated. My subway is a separate loop from the rest of my layout. When my subway set arrived new in the box it was DOA. Rather than pay shipping back to the seller (LHS couldn't get me the set i wanted at the time) or deal with MTH service (had one bad experience with them that took a letter from my attorney to get results), i simply removed the offending board (anyone want it - it's free for the asking and few dollars postage), picked up a used HO power pack for $5, and run it on DC. Converted all the lighting to LED's using a method similar to GRJ's (well before he started marketing his nice units).

jackson

Hello Jackson

Its not really that complicated although I admit it is not the most simplisitc of ways. You gut all the electronics.You get some LEDs,a bridge rectifier and a few diodes and resistors. Do a bit of wiring and soldering.These things cost a few dollars.

 When you do that you get:

Constant voltage lighting

An elimination of jack rabbit starts. 

The ability to stop the train and leave all the lights on.

Very long lasting lighting that should not need replacement.

No voltage distribution problem between motors as you get with series wiring and more pulling power. 

GRJ is a nice plug and play circuit but it is not constant voltage for conventional operators. Actually he linked a converter which was very helpful to me and simplifies my circuit.I never met John but respect him because he shares knowledge and his circuits for those wishing to do their own. I learn a lot from reading John's post. Still, I use individual LEDs. If you don't like the cars too bright the converters might even work with the 12 volt strips if you set it at 5 volts for conventional. 

My layout is forward only,I have done maybe 20 engines with the diode method. it works fairly well.  I have also done many sets of passenger cars and am happy with them. They stay lighted for a minute or more even if I pick them up and remove them from the track. Lots of ways to do things,I have my preferences. I found series wiring of motors not as good as my method. I used to wire in series and threw a lot of traction tires. 

I have seen even very expensive professionally built displays with flickering and burned out passenger cars.I have seen trains on display start and stop abruptly with all the lights going out when it stops. Really all this can be overcome with some basic electronic components. It is neither expensive nor hard.

Dale H

  I just can't believe how much trouble getting four lights to operate correctly is. Just when I think that I could settle on a way that would be acceptable it seems that it is not. With every question I ask it seems to just make another since every configuration seems to have yet another issue. That said I am so sorry for what seems to be an endless post regarding such. 

 This set up that I have with the four incandescent bulbs with my hot regulator heat sink which seem to be working fine otherwise was the best results that I achieved so far without any dimming or flashing ect. It being my second configuration to date. Though it seems that while it works that this is still not ideal or acceptable. Since you did not address whether it would be acceptable I know that you just absolutely hate it. LOL

But regardless is it ok to operate it as such until I am able to change it or I should not even run it like this at all ?

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 So I guess I will have to just redo it all again & this time the way that you suggest with the six, 6v diodes. However with all of the ways mentioned to date, just so I don't miss or mess up anything with all the info &  post to review, if you don't mind could you possibly provide a plan with the 4 leds that I ordered. If so, Please include motors in such.

  Since the leds I have on order have a 18v resistor built in which I believe will not need that chip mentioned previously & to avoid buying another component which I think may of been mentioned. Since I would not mind having the motors hooked up in a series to have more power to the unit as well as have it the same as the ones that come from the factory. All of which lights the additional coaches in the consist bright as welL.

 Hopefully I could still hook it up as such in the way you suggest with just diodes and the LEDs without the need to locate other components or anything else that adds any further confusion to me.

 Thank you...

I underatand from the rectifier to six 6v diodes / motor hookup, but after that with the new leds with the built in 18 v resistors I am not totally sure. Also would like to be able to use these resistors if possible as any other changes just add further confusion for me.

Also not sure if I hook up the motors like I want to if that messes up the way it is powered with this configuration.

Thanks

Kind of going over old ground here. There is a diagram up the page with the LEds and motors. The LEDs have polarity and they have to be right. You can find polarity by trial and error. They will light in one direction and not the other. If the motors run the wrong way you can reverse those wires. 

Yes you can use the existing LED with the supplied resistor,either directly to track power or off the diode string. Off the track power you need a 1 amp or more bridge rectifier,no capacitor. they might flicker a bit. Or the diode string if you make one. They might burn too dim for your liking. They will only get about 4 volts but will probably light. I don't have the LEDs so I can give you the colors of the wires. 

Running the 4 bulbs off the regulator and heat sink might work,but that regulator will use 2.5 times the bulb wattage at full throttle. twice as much at 12 volts throttle. the wattage will be used up as heat and not light.  Your problem illustrates why LED lighting is preferred for constant intensity.. I guess the power supply GRJ linked from China would give constant lighting with light bulbs without all the heat of a 7805 regulator. It might make the use of light bulbs palatable in passenger cars and cabooses. However they would be more prone to flicker I think.  I would suggest it if you insist on the bulbs but it might confuse you even more as it is yet another way to accomplish your goals.I have some of the converters and maybe could test it on bulbs to see how hot it gets.. Most everything I suggest seems to confuse you,sorry about that there are a lot of ways to do things and a lot of ways things should not be done. Running 4 lightbulbs off the 7805 regulator is not a good idea IMO.  But you are doing things contrary to what I suggest doing. You want the bulbs here is a possible solution. 

Here is a link to the Chinese AC to DC converter.

LINK

Such circuits are not new to me,but what is new is the low cost of buying something pre made like this.I retired 15 years ago and things have changed in electronics. Like I said,this MIGHT work driving bulbs,not sure how hot it would get.. This thing from what I read can be around 90% efficient. So driving 10 watts of bulbs might only generate 1 or 2 watts of heat. All this depends on what voltage you set it at you set it at. It is certainly more efficient than the regulator if you are determined to use bulbs.

Dale H

Ok so unless I am starting to lose track of all the options, it seems that this is my only option to use the LEDs and not have them dim or flash ect...

>> 

Hook them up from the regulator output circuit just like the bulbs. They are polarity sensitive and will light one way and not the other. The built in resistor is for a value of 18 volts and you are applying 5 volts so they will not be very bright. If it is not satisfactory, ""cut out the resistor and splice in a 100 ohm or more,1/4 watt or more resistor in it's place. ""

The 7805 should not need a heat sink with the 4 LEDs. At the very most it would use less than 2 watts.  Just leave some air around it and don't wedge it in an enclosed area. <<

However my only concern is that if you look at those leds I bought, the resistor is all the way up near the bulb and I don't think I will have enough wire to remove /replace with.

Just in case I gave the wrong impression, I do want to use the LEDs that I ordered. I just want them to burn correctly without experiencing the dimming or flashing issue that the original incandescent bulbs gave me thus far.

The marker lights will probably be bright enough off the 5 volts. The only way is to try them on the 5 volts. By trial and error you can find polarity off the regulator. they will light one way and not the other. If by chance they are too dim,take a razor blade or exact knife. carefully slit the insulation down the middle.Jump out the resistor with a small wire and some solder. Insulate with some shrink tubing or tape.  Then splice in a proper size resistor to either lead. 150 ohm or more,1/4 or 1/2 watt.  Insulate that. 

I looked at the listing,It says AC or DC compatible. If it has a bridge rectifier in the wiring,the LEDs will light in either direction. Without having one of the LEDs I can not say for sure. 

It says it has a 1000 ohm resistor in it. You can run that safely also off the track power with a bridge rectifier and capacitor. It will not be constant voltage that way but it will be flicker free.

Dale H

Those LEDs I bought are 

• Forward voltage:12V~18V(1000 Ohm resistor in series), AC or DC Compatible.

You say replace it with 100 or more but I guess in the low 100's and not as much as those ? Also I assume those 1000 ohm resistors are something other than 1/4 watt ?

Sadly I bought these hoping that they would help my cause. Now it seems that was not the case.

Oh I see that you have edited your post above just as I posted mine above.

Wiring those leds should not be an issue since they do have red and black wires.

The 1000 ohm should be half watt,but most likely they put a 1/4 watt in it. It is probably OK. The 100 ohm need only be 1/4 watt since it only drops voltage down from 5 to 3.The 1000 ohm has to drop from 18 to 3 or 15 volts. At 18 volts in it would use .3 watts,a shade over but in reality a quarter watt resistor would work.I am going to bed now,will check tomorrow to see how it all works.

Dale H

>>It says it has a 1000 ohm resistor in it. You can run that safely also off the track power with a bridge rectifier and capacitor. It will not be constant voltage that way but it will be flicker free.<<

Ok, if done this way. As of now I currently have a 8 amp rectifier with the motors hooked up to them. So if I scrap the DC lead over to the terminal post that I have with the regulator and capacitor. 

Then replace that with an AC lead over to a terminal strip, Then Add another rectifier which I have which is a 4 amp, Add the 35v cap you recommend with them and the LEDs grounded to the terminal strip which will be grounded to the frame. Then of course the rectified power to the bulbs. 

 Is this correct ? or am I a big failure. Lol

Yes

As I said it will not be constant voltage but it will be flicker free. A 220 uf or 470 uf 35 volt cap is fine. Pay attention to polarity. A backward cap will go puff. You can also just use the bridge that powers the motors if you put a 1n4001 diode in series and in proper polarity with one of the DC leads,then the capacitor. The diode will provent the capacitor from discharging into the motor circuit.

Dale H

>>The 1000 ohm should be half watt,but most likely they put a 1/4 watt in it. It is probably OK. The 100 ohm need only be 1/4 watt since it only drops voltage down from 5 to 3.The 1000 ohm has to drop from 18 to 3 or 15 volts. At 18 volts in it would use .3 watts,a shade over but in reality a quarter watt resistor would work.I am going to bed now,will check tomorrow to see how it all works.<<

Thanks, that was very helpful to let me understand how that all works.

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When I get the LEDs I will try it with the regulator and see what results I get.

 But if it doesn't work out I guess my next attempt will be to try the LEDs  as they are but by removing my current set up with the regulator and tring  it off of a rectifier instead.

Thanks so much for all of the info. Though I may get lost a bit along the way, over all  I really have learned a lot.

PS, though they will be variable off of the rectifier with the motors hooked up in series the unit gets plenty of power. 

Easiest way is to just use the motor bridge. Put a diode in series from one of the DC leads,then a capacitor. You can also use the second bridge rectifier. The 2 AC leads go to the rollers and ground. The + and - to the LEds in proper polarity. The capacitor across the + and - in proper polarity. 

Dale H

>>Easiest way is to just use the motor bridge. Put a diode in series from one of the DC leads,then a capacitor<<

Ok, so using 3 post of my 5 post terminal strip. If I take the DC off of my rectifier that I have for the motors and attatched it to the first post of my terminal strip, then jump a diode over to the next post, put the cap + to it, & the led +'s as well, then ground the cap and leds to the middle ground. Is that correct ?

Also in regards to diodes. Do the diodes have to be specific or would one of those 6v diodes be ok as well ? The same that you use in your 6 6v string.

Any regular type diode would work. I can't comment on terminal strips because I have no schematic. 

Dale H