# LGB F7B Adding Powered Trucks



## RioScott (Feb 9, 2010)

Have LGB F7 A & B Units. Have Purchased Additional Powered Trucks. Has Anyone Else Added Powered Trucks To Their "B" Unit. Having trouble with Wiring


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## sang_route (Sep 24, 2008)

If you want to replicate OEM just open the A unit and use it as a guide to make your own wiring harness. I think there might be a way to run just threw the blocks with no wiring to the body at all too.


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## wchasr (Jan 2, 2008)

Didn't someone here simply take an A-unit and swap chassis with the B-unit trucks and electronics to make an A-unit sound and a B-unit powered? I plan on doing just that at some point. 

Chas


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## acmartina (Jan 6, 2008)

Scott,

I have been thinking about doing this for a number of years, and recently picked up a pair of motor blocks on e-bay. I think there are a couple of issues to be aware of. First, the power that goes to the blocks on the A-unit goes through the electronics first, so if you wire the B-unit motor blocks directly to the track pick-ups, they will run at a higher speed than the A-unit. I have seen some posts here (by Dan Pierce I believe) talking about adding some diodes to reduce the current. An alternative that I think I will use is to run another pair of wires from the A-unit to the B, that tap into the wires going into the rear A-unit motor block. This way the B-unit motors see the same input. 

The second issue is around the reed switches that are embedded in one of the B-unit blocks. I have dissassembled one of the motor blocks before, so I think it would be relatively easy to simply move the guts of one of the new ones into the existing empty block with the reed switches.

As far as moving the sound to the A-unit (I presume so you can run it without the B-unit?), I would think it relatively easy. You would just need to trace the wires. 

Steve
Cypress, TX


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## Dan Pierce (Jan 2, 2008)

DO NOT ADD WIRES TO THE A UNIT MOTOR CIRCUITS!!!!!! 

The board in the F7A unit was designed for 1 or 2 motors, not 4 motors!!!! 


I have successfully added B sound to an A unit and made the speaker switch feed either a single A unit or 2 A units for speaker configurations. 

Also, I have successfully added a single motor block to the B unit and added wiring to the B unit with diodes added to speed match the B unit with A units. 
I have done this with 4 sets of AB units. 

Of course, you could add a LGB DC circuit board to the B unit and get speed matching. you just need to get the board and cables. 

Also, the B unit needs weight added when adding motor blocks. 

Please note that the B unit sound has a sensor on one of the axles and there is no gear on this axle. 

A gear must be added.


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## acmartina (Jan 6, 2008)

Dan,
Thanks for the heads up on running off the A-unit! What kind of diodes do you use? 
Steve


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## Dan Pierce (Jan 2, 2008)

To lower the voltage on a single or pair of motor blocks, I used a 4 amp bridge rectifier as this will give you a pair of back to back doides prewired if you just short/tie the + and - leads together. I had to add 2 or 3 of these to my F7B units to get the proper speed change. 

Why diodes and not just a resistor some will ask? 

A diode give a constant voltage drop regardless of the current/load on the motor, a resistor will not as the voltage drop across a resistor increases as the current/load increases. 

So I tie track power(left rail) to one side of a motor, then the other side of the motor goes to the ~(one AC connection) of a diode bridge. 
Other side ~ of the bridge goes to the other side of the track (right rail). 

If motor block is still too fast, I add an additional diode bridge in series to the motor. 

Diodes can drop either .3 or .7 volts each depending on what type is used. A bridge rectifier will give either .6 or 1.4 drop as you get a pair at a time. 

You could just use diodes and solder them back to back, but I find the bridge an easier solution, plus many have a mounting tab so I can mount them on the engine weight.


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## rthiele (Mar 27, 2014)

How would this look like when using DCC? 3 units ABA with 3 decoders. Would the speed matching for the B-Unit still be a problem? Other issues?


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## Greg Elmassian (Jan 3, 2008)

You speed match DCC locos with the CV's, start, stop, mid, and/or speed curve and/or custom speed table.

No reason to use diodes which would not give you the same flexibility and accuracy in the "matching"

Greg


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## rthiele (Mar 27, 2014)

Thanks Greg, what I thought. Am I correct that the power cable to an A-unit wouldn't be needed anymore and the sound could powered directly? How?


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## Greg Elmassian (Jan 3, 2008)

Dan is the expert here, if each unit has a decoder and speaker there would be no need to have wires between locos.

Let's see what Dan says.

Greg


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## Dan Pierce (Jan 2, 2008)

I would keep the track power (2 wirw cable) connected as 2 engines with power pickup run much better.
One motor block is easy to change in the B unit (no sound pickups in it). The sound motor block has a special axle for sensing wheel rotation and does not have a gear.
I only added a motor to the non sound pick up block, but kept the 2 wire cable intact for my ABA setup. I have not yet converted these to DCC, but when I do each will have a decoder.


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## Dan Pierce (Jan 2, 2008)

Oops forgot to mention that the LGB F7B sound motor block does not have power pickups nor does the dummy block.


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