Converting Mth PS units to forward only

In the past I have had two subways with defective PS boards and decided to remove the electronics and have a forward only power unit. I purchased a full wave bridge rectifier rated at 4 amps and up to 50 volts from Radio Shack (part # 276-1144). I am sure you can obtain a similar rectifier from a good electronics supply company. There are four leads coming out of the rectifier two of which get hooked up to your incoming a/c power from the track and the other two are the two d/c leads that go to the motors. From the d/c output I wired the two subway motors in series along with any lights I wanted. I have run those two subways for a few years and I am happy with the results. This was a very easy and cheap fix for me.

A full-wave rectifier connected to the motors' feeds would do it most easily, as N5CJonny did.  That is how I would do it.  Leaves everything else in place and working as it should.

You can find them on Amazon among other websites.  Generally when I buy one for locomotive purposes I get 6 amps, because it will run a bit cooler, but 4amps  actually ought to be more than enough.   

If there is nothing wrong with the boards, why not just leave them and use the lockout feature to lock them in forward?

Thanks for your replies..

So all that was used / needed was a rectifier ?

No Diode 
No Capacitor
No Regulator

???

Also does the 6v front marker light operate properly ?

No dimming or flashing ect ?

Just to be clear, the failed boards have been completely removed leaving nothing but the motors

All I needed was that bridge rectifier and the motors wired in series. The reason I wired the motors in series was because the subway ran much too fast if I didn't wire them that way. On my subways one of which was a LOV and the other a R17, the bulbs I believe are all 18 volt bulbs. I do not remember if I had to wire any bulbs in series or not, but you can test the voltage after the bridge rectifier is installed and see if the voltage is within a safe operating range for the bulbs. I have had no issues of flashing or dimming of the bulbs. Of course once you have this setup you will not be able to have a neutral standing state where you can view the lit interior while the subway is stopped. To get around this you could either install an e-unit or you can stop just the motor car up ahead of the train and still have the trailing cars lit.

I believed both boards on my subways to be burned out. If I had tried to have them just checked out, it was going to cost me more than I was willing to pay. The R17 had the old 5 volt board and I understand there are no replacement parts for those. I decided to pull out all the boards to give me all the room I needed leaving only the motors intact. I suppose you could leave the boards intact in the subways if so desired.

If this was a ProtoSounds engine (PS-1) you could remove the top board and place a jumper in the bottom board to get fwd only motion.

If this was PS-2 5V board that went bad, clip the Rectifier off the board.  This is the square black device the heatsink attached to.

If you clip it as close to the board as possible, you will have the 4 legs available.  You can use the heatsink to keep it mounted to the chassis.  Solder the red wires to one ac input, the black to the other.  Solder the white motor leads to the - and the yellow to the +.  You now have an 8 amp forward only DC rectifier and you did not have to buy anything.  G 

Thanks 

Sorry, I don't think that I mentioned it, but this unit was a 5v and the boards have been removed.

Also appreciate the PS 1 info for any future conversion  

Not sure what this means

>>or you can stop just the motor car up ahead of the train and still have the trailing cars lit.

What I meant was that you could have a small section of track say 20" in length that is isolated from the other track. By having this you can stop just the motor car on the isolated track and have the remaining cars on the active powered track. By doing this and using a simple on/off switch to control the isolated track you can have most of the cars lit up when the subway stops. In my case I had the isolated track controlled using an old Lionel 115 stop station and then I could have the subway stop and start automatically. By using old technology I was able to achieve what I wanted Which was to stop and start the subway automatically and have most of the cars lit when the subway stopped. I hope I made myself clearer on this.

Oh ok, great idea. I like how you improvise. Exactly what I like to do and this is something that is most certainly a perfect way to achieve satisfaction :-) 

Thanks much..

Now in regards to the conversion to forward operation only.

Just to confirm that I am understanding this correctly.

If I am to strip a powered unit down to nothing but motors and lights.

All that is needed for forward operation only is -

a full wave bridge rectifier rated at 4 amps or 6 amp and up to 50 volts 

& no other components ?

Not even a regulator ?

Thanks in advance...

Yes.

Thanks..

One last question.

In case certain ones are more readily available at any paticular time.

What would be the minimum as well as maximum for such.

I know that 4amp would be the minimum. 6amp is good as well. But would a 8amp also be good if my only choice was 4 or 8 or would 8 create some sort of possible problem otherwise ?

Also, What would be the minimum / maximum for wattage ?

"""Thanks so much to all who have taken the time to reply """"

If you email me, I have a 4amp one I will send to you.

Thanks but the larger one will be easier for me to work with at this time

From what I understand the interior bulbs are 18v which is fine to hook up this way. However aren't any of you blowing the bulbs on the marker & head lights which are only 6v ?

Didn't have much luck with a regulator. For some reason the lights would start to dim ect. Not sure why. I had a capacitor hooked up with it.

Figured I would give the resistor a try. I went to radio shack and they had four draws of resistors. So I had no idea which one to get. 

Somewhat off the path a bit,  but I have some early MTH (first run GP-9 in Southern and Union Pacific) without sound.   They came with a switch (two actually I think) to lock in run direction state and and the second to determine start up direction.  Same final objective and you could have it start long cab forward for a geep,  again off the path a bit from your interest here but looks like early QSI non sound boards may have a possible solution also.

Mark

A better way IMO is to use 2, 6 amp diodes for 2 motored units. The reason is that with 2 diodes the voltage will always be distributed evenly. Each motor will receive opposite halves of the sine wave.  In series wiring the resistance can change from one motor to another as the loco rounds a curve. Instead of using 2 diodes,3 leads of a bridge rectifier,10 amp or more can be used instead. Run one wire from the outer rail ground to one lead of each of motors. Run the wire from the rollers to one of the AC leads of the bridge. Then run the + and - of the bridge leads to the remaining 2 motor leads. Direction can be reversed with a switch. 

You don't need a capacitor but could add a small value one ,say 470 uf ,35 volt across each motor leads to smooth things out. These are not large enough to significantly increase voltage to defeat the purpose of the half wave DC.   

Another way is to use 4 leads of a bridge and then put a string of diodes in series.This is my preferred method. Shown here

LINK

The leads of the string can then be tapped for constant voltage lighting.

A second way to do the headlamp is shown here

LINK2

If the diode string is used with 6 diodes in each direction, leaving 5 volts on the track will starve the motor ,stopping it while the CV LED headlamp stays on at full intensity. If CV LED lighting is installed in the cars,they will remain lit at full intensity at the 5 volts when the train stops. 

CV lighting for passenger cars is described here

LINK3

and here

LINK4

Some better pic here

LINK5

Dale H

Hi, thanks, where can I pick up this CL2-n3 chip and LED lighting ?

Would like to try the chip next time.

Right now I have a bridge rectifier with the DC + over to a 5v Regulator with a 25v capacitor going back to the - dc of the rectifier.

For some reason the original mth 6v lights would only stay regulated basically at start up and when enough power was added to move the consist they would dim out. Upon slowing down they would brighten and become fully regulated just before powering off. 

I don't understand why they would even react this way. I would of thought that this would of worked just fine. But it didn't .

This was my second attempt over this dim or flashing light issue. Besides the way I just described the other attempt I took the AC lead over to a terminal strip, rectified over to a capacitor / regulator , cap & reg to ground,,,, positive regulated to markers/headlights & their grounds out to terminal ground.

The lights reacted a similar way.

Idealy I would like to use the LED lights you mention. But I am guessing that I would not be able to use them off of what I have set up this at this time with the 5v regulator ??? That is to much correct ?

Needless to say I have since damaged a bulb and have now given up on the original mth markers.  So led is really my only option I would think, unless someone knowss of a regular buld assembly that would be small enough to fit in the marker light holes.

Thanks

MTH PS-1 bulbs were 1.5V for headlights.  They were powered across 2 diodes to get the 1.2-1.4V drop.   If it was a premier engine with other light features they used a 6V regulator assembly (some simple and some complicated) to power those 6V lights such as interior or Number board, other interior lights such passenger area are 18V.  Steam headlight was always 18V track power since there were not enough wires in the harness to connect to the PS-1 board in the tender.  So only diesels had 1.5V headlights.  Premier steam could be CV 6V because of the CV board.  There are a few exceptions.

LED Markers were parallel wired and ran of the PS-1 board at 3V for diesel, or they used the CV board with a current limiting/voltage drop resistor.

For the motors AC input power went into the FWBR first.  The + output goes through 2 of the 6A diodes in series.  Followed by the last 2 diodes in parallel.  One output to fwd relay and one to reverse relay.  This gives a 2.4 - 2.8V drop of input voltage to motor voltage for slower operation of the engine.   G

I get mine for Mouser

LINK

I run conventional and circuit LEDs for constant brightness at all throttle ranges. A discussion about LED car lighting is here

LINK2

The red markers can also be circuited with the Cl2-n3 chip or you can use a resistor. In my experience the red markers get too much voltage off the PS1 board. Red LEDs only drop 2 volts usually.  They should not burn out but I have replaced several ran off the PS board. I altered the wires and wired the red ones in series. On your below post,any capacitor off track voltage should be 35 volts or more. 20 volts from a PWZW rectified peaks around 28. 18 volts peaks a bit over 25. 

Reading your other post. If you use the 5 volt regulator each LED will need a resistor to it. 100 ohm is fine for white. 150 ohm for red. If you follow the drawing in the link,the resistor is in there. 

Dale H

Hi, the subway unit was previously a 5v ps2 board. I was told that in interior lights are 18v and the marker lights that have been giving me so much trouble were 6v.

I hooked them up as mentionped above in my previous post. Not sure why I had so much trouble with them. But needless to say I damaged a bulb an now have given up on them. So I am looking to replace them now. 

But I guess my regulator set up will not be adaquate for any possible replacements. That being a higher voltage bulb which all seem to be to big to fit and the 5v to much power for the LEDs. So I guess my best option is to get the LEDs and use a resister ?

I would use LEDs with either the regulator or CL2-n3 chips. The chips are easy to circuit and need no resistor calculations. See the posts I deviously linked.

Dale H

Will do,,thanks much.

Does that site with the lc2n3 have those particular LED lights ? I looked a bit and did not find them so far.

I get the LEDs from Ebay from a China supplier. They can be purchased in various quantities cheaply

LINK

LINK2

In regards to the optional capacitor with the cl2n3, since you say optional would it be beneficial to use the 25 v ones that I already have over none at all or should it be the35/50 as mentioned.

Also since it is optional, what is the differences with verses without ? TY 

Hi, as you can see I am just starting to look into and learn about all of this. That said I don't really understand why I had such a problem with the original mth incandescent 6v bulbs. Other than based on what I have been reading from your post the only thing I think that it may of been is perhaps that 25v capacitor since you mention a 35v or better is required.

With the cl2n3 are the LEDs to be hooked up in sequence or that did not matter when using that component. thanks again..

If you use the cl2-n3 chip,you need a capacitor and 1 bridge rectifier per car. Any capacitor hooked to track voltage should be at least 35 volts. 25 volts is not sufficient. 100 uf or more is fine. Not sure how you hooked up to the 6 volt bulb or what the problem was. 

Each LED needs a CL2-n3 chip for constant voltage lighting if the LEDs are wired in parallel. 

They make 1.8mm LEDs,3mm 5mmm 8mm and 10mm etc.  Perhaps someone has a source for the small ones. The LEDs should give off little heat and not red replacement. 

Dale H

Hi,

Measuring the subway lights that 1.8 looks to be what I need. Thanks I needed that for the search. So far the smallest I came up with was 3mm.

,,,

Ok, found the following.

Warm white

I have the square surface mount bridge rectifier. 

The motors are hooked up in sequence.

At this time

I have a separate lead from the d/c going over to a terminal strip With a capacitor 25v and a 5v regulator. Not using the terminal ground & have a return back to the DC-.

So based on what I have set up here.

I just need to remove the regulator and inadequate capacitor set up.

Then instead have the dc lead over to a terminal strip with a 35/50v capacitor and one cl2 n3 chip wired in sequence to the bulbs with a return back to the DC-

Will that do the trick or should I set it up another way ?

Thanks again..

UPdate,,,

PS, I have read the following.

>>One or more LEDs can be put in series with the chip. As always series wiring is more efficient.As many LEDs can be put in series as voltage input allows. 20 volts will drive 6 for example. However for conventional each LED will need a chip since 5 volts,the minimum throttle setting will only drive 1. However for building wiring LEDs in series is practical. A good use for this chip is circuiting a constant voltage headlamp. The circuit is not practically dimable.

"""I do run in conventional with 75 or 100 watt transformers. Not sure how many volts I get up to while running on a decent speed. But I was wondering if using only 4 bulbs pulling three or more coaches would that be adaquate for the one chip. """ Or no way and I could possibly get away with using "one chip per each set of lights"  rather then one for each Light"""

You can check out what forum sponsor Evans Design offers. You can get 1.8m LEDs set up to work off your ac power (their universal LEDs). I've used their LEDs often and I'm very happy with the ease of installation and their long life.  A slight bit more expensive but there ease of installation easily makes up for the added cost.       Lenny J 

I bought the following.  Pre-Wired-1-8mm-WARM-White-Led-Lamp-Light-Set-12V-18V they have a built in resistor.

I have read the post regarding LED lighting. At this point I don't know which approach to use. I just want 2 headlight & 2 marker lights that don't flash or dim on their own or any over heating components.

So the question is, what is the easiest way that would be acceptable to operate in conventional mode off of a 75 or 100watt mth transformer ? 

Can I use them as is straight off of my rectifier or should I hook them up to the set up I have and described above ? Or buy & use that cl2n3 chip ?

Also with either way should I hook up the bulbs in parallel or in sequance ?