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Is it the decoder?

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Is it the decoder?
Posted by Soo 61245 on Tuesday, July 8, 2008 1:02 AM

I've just finished hard wiring a Digitrax DH163D into a Walthers F40.  When I tested it, setting my DT400 throttle to forward, the forward headlight is on but the engine goes in reverse.  Changing the throttle to reverse, the rear headlight goes on and the engine goes forward.

Yes, I've double checked the wiring and its correct as shown in the instructions, red wire to engineers side, black wire to fireman's side, orange to + motor side and gray to - motor side.

If this a problem with the decoder?  Can I change a CV before cutting and reversing the wiring?

 

john

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Posted by Vail and Southwestern RR on Tuesday, July 8, 2008 2:44 AM

The easiest thing to do is to swap the orange an grey wires.  The motor is wired backwards, for whatever reason.

There is a CV you can play with, but if you use it, and you reset the decoder, or possibly even consist in some ways, you are going to end up with more confusion in the long run.

Jeff But it's a dry heat!

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Posted by jeffrey-wimberly on Tuesday, July 8, 2008 6:01 AM
 Vail and Southwestern RR wrote:

The easiest thing to do is to swap the orange an grey wires.  The motor is wired backwards, for whatever reason.

Swap the motor wires. That's the easiest fix I know.

Running Bear, Sundown, Louisiana
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Posted by MisterBeasley on Tuesday, July 8, 2008 9:02 AM
 davidmbedard wrote:

Yup, there is not standard for + and - for the motor.  You always have a 50/50 chance to get it correct the first time.

David B 

50/50 is the "statistical probability."  However, Murphy lives in the real world, so you've only got about one chance in 4 of getting it right.  Whistling [:-^]

Seriously, I think you'll usually get it right if you connect the orange wire from the decoder to the side of the motor that used to be wired to the right side of the engine.

It takes an iron man to play with a toy iron horse. 

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Posted by Soo 61245 on Tuesday, July 8, 2008 9:23 AM

Thanks everyone.  I'll reverse the wires to the motor.  

 I had just done another unit, a Walthers Dash 8 so the motor/chassis is basically the same.  Based on that, I wired the F40 the same.  Seems strange that the connections from the motor would be reversed??

john

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  • From: Orig: Tyler Texas. Lived in seven countries, now live in Sundown, Louisiana
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Posted by jeffrey-wimberly on Tuesday, July 8, 2008 9:28 AM
 Soo 61245 wrote:

Seems strange that the connections from the motor would be reversed??

Fact can be stranger than fiction. I have an Athearn loco (SW7) that ran backwards when all my locos ran forward, and vise versa. A quick check revealed that the motor casing was upside down, this putting the - side on top instead of on the bottom.

Running Bear, Sundown, Louisiana
          Joined June, 2004

Dr. Frankendiesel aka Scott Running Bear
Space Mouse for president!
15 year veteran fire fighter
Collector of Apple //e's
Running Bear Enterprises
History Channel Club life member.
beatus homo qui invenit sapientiam


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  • From: Christiana, TN
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Posted by CSX Robert on Tuesday, July 8, 2008 12:21 PM
 MisterBeasley wrote:
 davidmbedard wrote:


Yup, there is not standard for + and - for the motor. You always have a 50/50 chance to get it correct the first time.

David B



50/50 is the "statistical probability." However, Murphy lives in the real world, so you've only got about one chance in 4 of getting it right. Whistling [:-^]

Seriously, I think you'll usually get it right if you connect the orange wire from the decoder to the side of the motor that used to be wired to the right side of the engine.


Actually, there is a standard for + and - on the motor. The terminal that is wired to the right hand rail is considered +. The reasoning for this is because according to the NMRA standard, applying a positive potential to the right hand rail results in forward motion. As long as the engine ran correctly on DC, if you run the red wire to the right rail(and the black wire to the left rail) and the orange wire to the terminal that was connected to the right rail(and the grey wire to the terminal that was connected to the left rail), then you will get it right every time.

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Posted by locoworks on Tuesday, July 8, 2008 12:46 PM
every now and then a loco comes out the factory with the motor fitted 180 degrees out. as said above just swap the grey and orange wires. if you have cut a wire to short to allow it to reach the other terminal, strip the motor out and turn it 180 degrees and put it all back together with the wires going to the same physical place which is now the opposite pole on the motor.
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Posted by Vail and Southwestern RR on Tuesday, July 8, 2008 1:01 PM
There are a bunch of ways the motor can get flipped, and if you haven't marked it before you start taking things apart, there's a pretty good chance that by the time you are done, you'll have it backwards.

Jeff But it's a dry heat!

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Posted by Soo 61245 on Thursday, July 10, 2008 9:56 PM

I've now reversed the wires to the motor of the F40 and it's forward/reverse orientation is correct.  But now another quirk....

After a few minutes of running on my test loop, the engine stops but the headlight remains on.  I'm finding that just one click of the throttle nob gets it moving again.  Or, it would stop, with headlight burning, and then just begin moving again in a few seconds, on its own. 

While it was stopped, tapping or moving the engine would not get it going again, as it might if running on DC. 

Any ideas?

john

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Posted by CSX Robert on Thursday, July 10, 2008 11:09 PM
It sounds like you have the engine selected on more than one throttle. If the other throttle is set to stop, it will occasionally take over control of the engine and it will stop. If you let it sit for a while, control will eventually pass back to the first throttle and the engine will start going again. Turning the knob makes the first throttle take over control immediately.
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Posted by Soo 61245 on Thursday, July 10, 2008 11:38 PM

CSX Robert:

   Thanks, I think that's what I've done. Still have this engine addressed to 03 and I did have the other throttle selected for 03.  I also need to re-read the part about "dispatching" engines before shutting the system off. 

   I just ran this engine again and this time, no problems but I know there wasn't an address selected on the other throttle. 

john 

 

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