# Correct loco polarity?



## bluenavigator (Aug 30, 2015)

I am working on the used Walters and Athearn locos. 

I have Athearn GP35 (which I got from eBay) and I completed cleaning and oiling drive train. It runs pretty good and I am happy with the result. 

I have Walthers GP15 (which I got from train show) and tested it before doing clearning and oiling, I noticed that the polarity is opposite from the Athearn one.

I am pretty sure that it is standard to have the polarity standardized for every loco, correct? 

Since the Athearn loco could not have the polarity reversed, would that mean that the Walthers have the polarity backward? 

It is my first Walthers that I own.


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## Brakeman Jake (Mar 8, 2009)

The standard polarity is positive to the right side wheels for the loco to go forward running on DC.

One of your locos has likely been assembled reversed.An exception to the rule are high hood locos that may be set to run short hood or long hood forward as this differed from different railways.


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## DonR (Oct 18, 2012)

Are we correct to assume you are running DC?

If so:

The headlight and reverse lights work using
the track polarity and diodes to cause the right one
to come on. If they match the direction of the
loco you'll want to flip the wires from the trucks
to restore correct forward/reverse operation. 

If the lights don't match the direction, flip the
wires to the motor only.

Don


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## time warp (Apr 28, 2016)

If you don't have a meter, use a 9 volt battery on a short piece of track. Touch the battery across the rails with the + terminal on the right hand rail. The locomotive should then move forward if polarity is correct.


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## bluenavigator (Aug 30, 2015)

Thanks for suggestions. I took 9 volts battery to one of known good switchers and it goes in correct direction as I applied positive pole to the right side of the switcher. Then I checked the direction that it goes on the test track and confirmed that it is set up correct for the direction switch on the MRC transformer. Perfect! 

Turned out that it is the Athearn one that has the polarity backward. Since it is not possible to do rewiring on the Athearn, as there is no wiring. I removed the motor and turned the magnet 180°. Now it is going in the correct direction.


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## time warp (Apr 28, 2016)

Glad you figured it out, my money was on the Athearn being wrong.


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## crusader27529 (Apr 3, 2016)

bluenavigator said:


> Thanks for suggestions. I took 9 volts battery to one of known good switchers and it goes in correct direction as I applied positive pole to the right side of the switcher. Then I checked the direction that it goes on the test track and confirmed that it is set up correct for the direction switch on the MRC transformer. Perfect!
> 
> Turned out that it is the Athearn one that has the polarity backward. Since it is not possible to do rewiring on the Athearn, as there is no wiring. I removed the motor and turned the magnet 180°. Now it is going in the correct direction.


The athearn trucks can be installed swapped (front to back, not rotated in the correct location), and all will work, but obviously reversed polarity.

My guess is that it was done so when in an MU set, so it went the correct direction as required. Reversing the trucks obviously would also have worked.


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## bluenavigator (Aug 30, 2015)

crusader27529 said:


> The athearn trucks can be installed swapped (front to back, not rotated in the correct location), and all will work, but obviously reversed polarity.
> 
> My guess is that it was done so when in an MU set, so it went the correct direction as required. Reversing the trucks obviously would also have worked.


I am not sure about swapping the trucks. That is interesting. When I disassemble the loco, I put all the parts in the order from front to rear. That way, I can put them back together in the correct order. The only thing, that I could not tell is the magnet, itself. It does not show N and S marks at all, it is 50/50 chance, being correct.


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## Mark R. (Jan 26, 2013)

Yes, Athearn trucks can be installed "backwards" on some of them causing them to run the opposite direction. Just remove the trucks, swap ends and re-install.

As for somebody reversing them so they could mu the engine with another facing the opposite direction - that's not true. On DC, if an engine is running to your right and you pick it up and turn it on the track 180 degrees, it will still run to the right.

Mark.


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## crusader27529 (Apr 3, 2016)

Mark R. said:


> As for somebody reversing them so they could mu the engine with another facing the opposite direction - that's not true. On DC, if an engine is running to your right and you pick it up and turn it on the track 180 degrees, it will still run to the right.
> 
> Mark.


I stand corrected.....guess I'm getting too old......


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