I have a problem that I wonder if any of you can help me with. I have a BLI EMD-SD40-2 loco on a DC layout and also an older Athern diesel that was given to me. I’ve read all the posts but can’t find one that helps with my problems. The problem is that when I put the Athern on, it goes the opposite direction from the BLI loco. I have 2 DC packs running with an inside/outside track configuration (one Tech 2 and one Tech 4) where they have turnouts to connect the two tracks. The Athern runs the “wrong way” and when I went to run it from the inner track to the outer track with the BLI running on the outer, it shorts out the track and stops them both. I took the shell off the Athern and with the cab light up front, it’s not possible to put the shell on the wrong way. Anyhow as a test, I tried to rotate the loco 180 degress on the track and the same thing happened; Athern went “left” while the BLI went “right”. There are two wires to the motor, one from the front truck to the front of the motor and one from the back truck to the back of the motor. I tried to change these wires and made the back truck go to the front of the motor and the front truck go to the back of the motor. Put it back on the track and the same problem. It still runs opposite the BLI. Can anyone help me as to how to get this Athern to “flip polarity”? Thank you for any help!!!
switch the wires on the terminals on one of the power supplies(only one). This should solve the problem, I think the polarity is switched this way judging from what you describe is happening, should have no problem with any brand of loco being wired differently. I have over 75 locos and they all run the same direction. Good Luck
Thanks for the quick reply!! The thing is that if I only run the BLI loco, it runs fine from inner to outer and so forth. If I put the BLI and the Athern on the same track (right next to each other) and put some power to the track, one goes left, one goes right. I think the Athern may have had a “non stock” motor put in it but I just cant figure out why or how it goes in the complete opposite direction as the BLI loco no matter what I do. If I put them right next to each other and switch the wires to the power pack, well, um, yeah, not a very good idea. Not too bad if they go opposite directions like they did at first, but when I changed the wires on the pack, well, you get the point. LOL. Thanks for helping me try to figure this out!!
I thought the problem was only when going from inner to outer, but if on same track then as you assumed the polarity is switched on one of them, probably the athearn if it does indeed have a after-market motor. I am unsure which wires you would have to switch though. Good luck in your quest to rectify the problem.
The basic rule is that a DC locomotive is supposed to travel forward when the right-hand rail is positive and the left-hand rail is negative. Determine which rail is which, and you’ll have determined which locomotive is mis-wired.
Assuming that both motor brushes are wire-connected, just switch the wires to the opposite brushes.
If there is some other brush connection arrangement, you might be able to get the same result in some different manner. The most drastic might require turning the motor end for end in the frame, if that’s possible.
Chuck (Modeling Central Japan in September, 1964 - anaog DC, MZL system)
Since you said the older Athearn model was given to you, there may be the possibility that the previous owner had it apart and installed the trucks on the wrong ends. They are simple to take off and replace, give it a try and see. Either way this will change the polarity to the motor and change its direction. I know this because it’s happened to me in the past.
FIXED IT!!! Thank you very much for the help. The problem was the trucks. I took them off and switched them around like you said and now it works great and goes in the “correct” direction with the other loco. Thanks again for your help. I just could not figure that out.
Bob’s suggestion is right. Swap the trucks front to rear. These are all permanent magnet DC motors and the direction of rotation is set by the polarity of the DC drive voltage. Swap the polarity and the motor will turn the other way. Turning the shell back to front isn’t effective, the chassis doesn’t care, doesn’t know which way the shell is on.
You want all your locomotives to run in the same direction so you can double head them and not have them fight each other.
The rail polarity rule quoted previously is most likely correct, but I have great difficulty telling my left from my right, and deciding which end of a road switcher is front, which wheels are on the left or right and other confusion factors, that I would pick one locomotive as the standard, and make my other locos conform to the standard. BLI is fairly new whereas Athearns can be as old as the hills. A new BLI which you bought your self and haven’t taken apart is a better standard than an older Athearn whose history you don’t know. It is pretty easy to take an Athearn apart and put it together running in reverse.
The ordinary Athearn, a blue box kit, of which many of us have a few, is a hot chassis locomotive. The trucks electrically connect the wheels on one side to the chassis, which makes contact with one motor brush, the one on the underside of the motor. The wheels on the other side connect to steel straps on the trucks which wipe against a steel wiper ba