Converting an LGB 20882 Mallet
Converting an LGB 20882 Mallet
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Converting an LGB Uintah #51 Mallet to DCC can result in a vastly superior locomotive. For this conversion I chose two Lenz LE-131 decoders (one for each motor) because of their superior back emf features. While many other decoders can be used, the superior slow speed control of a back emf decoder is ideal for this conversion.
One of the most difficult parts of this conversion is taking apart the Mallet. Unfortunately LGB provides no diagrams. There are 9 screws that must be removed in order to remove the upper boiler and Cab assembly.
Once these 9 screws are removed the upper boiler can be removed from the locomotive.
There are several components you will not need in the conversion. The front LGB circuit board (#20882-153) Is a voltage regulator and motor controller. It is this board that makes the mallet run so smoothly. This circuit board is no longer needed.
I also remove the switch in the Cab but if you desire to keep it can be retained.
The lights (headlight/cab light) are replaced with 19 volt lamps LGB #68513
I also recommend replacing the smoke unit with a 19 volt smoke unit. To continue to use the 5 volt smoke unit requires a new voltage regulator or a resistor. (I have jet to do this, any suggestions for a source?)
Unfortunately the LGB #20882-153 circuit board you remove is also the main junction point for the wiring in the Locomotive. What is needed from LGB is a replacement board that has DCC built in. Then the conversion would be a drop in replacement. (and likely less expensive to produce than the one currently in the locomotive). Alas to date such is not the case.
One either has to splice all the wires or build a new junction board. I chose the later. Since I found it hard to find similar connectors, I stole them from the circuit board I was replacing. However to do so invalidates the warranty for this board so the choice is yours.
The wiring of the replacement circuit board is simple. What one is doing is connecting on the wires together. I chose to use the NMRA medium plug for the decoders so that they could be removed and/or replaced. This is optional but highly recommended.
On this circuit board diagram, the front headlight is on the left, the two 2X4 connectors are the NMRA sockets, the lower LGB 4 pin connectors are for the front and rear motor, the top LGB connector connects to the upper frame and connects the cab light and the rear track connectors (behind the cab). The two bin LGB connector is for the sound unit. Only one wire is connected in this diagram. I will explain later.
Once this circuit board is built and installed, the locomotive can be operated.
To hook up the sound board simply connect the red connector in the above diagram to red wire in the diagram. This will turn on the sound unit and the whistle and bell will work using the existing track magnets. However you can do much better! First if you hook up the sound unit this way it will always be on. (With DCC, track power is always active.) I tend to desire to be able to turn my sound units on and off when desired.
To do this utilizing Lenz equipment, I use an LF-200 function module. The LF-200 is simply three relays. I connect the input for the first relay to the F1 decoder function output. The output of this relay is used to connect the power to the sound module. When F1 is active the sound is turned on, when F1 is off , power to the sound module is removed.
To make the Bell and Whistle work with DCC functions, simply hook
F2 and F3 from the rear decoder to the same LF-200 function module.
LGB provides a convenient 3 pin connector on the sound module
just for this purpose. Hook these wires up to the function module
and when F2 is pressed the Whistle Blows and F3 turns on the bell.
The completed circuit board with the LF-200 installed is shown in the photo. The decoders are placed below the circuit board in the space left by LGB.
I program both decoders with the same address. However I program the acceleration rate to be much quicker for the front engine than for the rear engine. Why? On the prototype, if the engineer accelerates the locomotive to fast, the front drivers slip. By programming the acceleration rates differently, the same effect can be had on the model. Accelerate slowly and all is well, Accelerate quickly and the front drivers slip.
You also need to program the rear decoder to use functions 1-3 rather than the normal headlight. To do this program register 7 to have a value of "4".
The use of DCC functions is only limited by your own imagination. Here are some simple suggestions.
Last Updated March 16, 1996
Copyright 1996-2007 by Tried & True Trains,
Inc.
This page is written and maintained by: Stan Ames
For more information contact Debbie Ames,
President tttrains