PS-2 Directional Lighting

[Anonymous]

Hi All,

I have MTH ps-2 in a diesel (5 volt board). It uses one big 6v lamp. Does any one know of an easy way to convert over to directional constant intensity lighting (preferably using a pair of 1.5 v mini-lamps?
I have the Kalmbach book "Easy Electronics projects for Toy Trains" but that seems to be before the Protosound era. I even bought the 25 amp "Mother of all Bridge Rectifiers" as they recommended but after looking at it I figured there's gotta be a better way.
I checked the plug where the lamp wiring exits the board for a possible 1.5 v tap (similar to that on a Locosound board) , but couldn't find any. Any suggestions?
thanks,
-Mike

[lionelsoni]

Directional lighting is trivial for a traditional universal-motor locomotive. But it might not be too difficult if, as I imagine, yours has DC can motors. You can do it the same way that scale modelers have been doing for years. That is a circuit that goes in series with the DC motor(s). It comprises 6 rectifier diodes. Wire all 6 in series, all pointing the same way, in a complete loop. Make 2 connections to that loop, 3 diodes apart, so that there are 2 strings of 3 diodes, and put this in series with the motors. Then wire a 1.5-volt lamp across any 2 diodes in each string.

The diodes need to be able to handle the motor current; so I would use at least 3-ampere parts. This circuit will drop the motor voltage by 2 voltts or a little more; so you will lose some of the top speed. (Some would say that is not a bad thing for a toy train!)

[Anonymous]

Thanks, Lionelsoni,

The method you describe looks like a winner but I have one question. You mentioned wiring the circuit in series with the dc motors, however each motor has its own set of wires on a plug coming off the main board. Should I , in this case, run a separate circuit off each motor?

-Mike

[lionelsoni]

It's possible that there is a good reason for the separate wiring. If so, you do need to duplicate the diode network for each motor, so as to keep the motor voltages similar. In that case, you could replace one diode network by a pair of bridge rectifiers. For each bridge, wire the + and - terminals together and to one of the ~ terminals of the other bridge. Then use the two so-far unconnected ~ terminals to wire the whole mess in series with a motor. This will likely be more compact than six individual diodes.

I suspect however that the sockets for those plugs are simply wired in parallel on the circuit board. If you can get a good look at it to verify this, then you can go ahead with the original plan, just using one of the plugs for both motors.

Either way, you can also implement the 6-diode network with three bridge rectifiers. Within each bridge, connect the ~ terminals together. Then connect the + terminal of each bridge to the - terminal of another. The resulting ring is equivalent to the 6-diode ring. You can consider the current rating to be double whatever the bridges are rated for, since there are actually 12 diodes in the new ring.