# Speed Matching Usa Trains with Aristocraft



## shayboy1420 (Jun 18, 2010)

Hello all,

Over christmas I received a USA trains SD70Mac and a Aristocraft GP40. I took them down to the club I run at and checked the speed. The SD70 is much faster than the gp40. I would really like to run these two locomotives together since thats why I got both. Because I don't have my own layout I can only run at the club i belong to, so i cannot us DCC and such to speed match. I have heard that you can use resistors but I don't know exactly how to go about doing that, what kind of resistors and things like that. I really want to run these two locomotives on DC power together without having to make one a dummy. Any advice is appreciated. 

Thank you,
Zeb


----------



## Greg Elmassian (Jan 3, 2008)

Use strings of diodes, they generate less heat, and you only need to drop a few volts. 

Using resistors adds a nonlinear relationship (does not work as well) 

you put 2 diodes in parallel, but they are in opposite sense to each other... then you splice this into one of the track pickup leads.. this will drop .7 volts... add more pairs to drop more voltage. Use 5 amp 50 volt (minimum) diodes. 

Make sure that (for example) BOTH the right hand pickup wires go through your "diode string".. 

Here's a picture of a lower current one I made for a small loco, drops 5 x .7 volts, i.e. 3.5 volts in both directions










Regards, Greg


----------



## lownote (Jan 3, 2008)

I've done what Greg describes, it works very well but you'll have to do some guessing about how many diodes. Diodes are electronic components that only allow current to pass in one direction (http://en.wikipedia.org/wiki/Diode). So you would need sets of say 4 diodes facing the same way for both of the two motor leads--so current passes in forward and reverse. 

Diodes have an amperage rating--to be safe I would get some 6 amp 50 v diodes like these from radio shack(http://www.radioshack.com/product/index.jsp?productId=2062583). They come four to a pack. I'd get four packs. Orient them so they are joined end to end, silver to black, silver to black, and then on the other motor lead, orient them facing black to silver. black to silver. 

Sounds hard, but it's not


----------



## toddalin (Jan 4, 2008)

When I do this, I solder them up, side-by-side, head-to-tail and just enclose them in a piece of heat shrink tubing.


----------



## Greg Elmassian (Jan 3, 2008)

To test, you can jerry-rig up a single string, and test in one direction, add more or take one off until you get the matching you want. 

Then when you know the number of diodes, solder up the "pairs" and make it neat and tidy. 

Greg


----------



## Dan Pierce (Jan 2, 2008)

It is easier to use a diode bridge and just place single diodes between the + and -. AC goes between power source and 1 motor lead.


----------



## Greg Elmassian (Jan 3, 2008)

Forgot that trick, we did discuss before. In my case above was a very small loco and 5 drops using 10 diodes was smaller than a packaged FW bridge and 5 diodes. 

But the simplicity of what you say Dan is nice! I need to add that tip to my site. At 6 diode drops and above it uses fewer diodes total. 

Regards, Greg


----------

