Engine polarity

Engine polarity

Postby Rob M » Tue Mar 25, 2014 10:37 pm

On the layout below, should a dc engine run clockwise or counter-clockwise?

Image
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Re: Engine polarity

Postby ConducTTor » Tue Mar 25, 2014 11:50 pm

Depends. Which way is the engine facing, and are the terminals on the engine wired with the same polarity as the track? Also, how is the motor wound and what are the polarities of the magnets in respect to the motor coils? Long story short, it will run in one direction or the other :)
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Re: Engine polarity

Postby ctxmf74 » Tue Mar 25, 2014 11:59 pm

Positive power to the right hand rail should give forward motion so on this loop that would be counter clockwise? ......DaveB
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Re: Engine polarity

Postby krokodil » Wed Mar 26, 2014 2:04 am

ctxmf74 wrote:Positive power to the right hand rail should give forward motion so on this loop that would be counter clockwise? ......DaveB

That is correct, the right rail should be positive in case of forward motion.
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Re: Engine polarity

Postby AstroGoat760 » Wed Mar 26, 2014 2:11 am

Rob M wrote:On the layout below, should a dc engine run clockwise or counter-clockwise?

Image


From the NMRA S-9 standards, last revised August 1984:
http://www.nmra.org/standards/sandrp/s-9.html

II. CONTROL
A. Direction control by polarity reversing shall be provided. Positive potential applied to the right hand rail shall produce forward motion. (3)
B. Speed control means by voltage/current reduction shall be provided.


So much as the locomotive is wired as per NMRA specs (most, but not all, are. Pretty much every DC loco made in the US from the 1950's on is in this group), and is under conventional DC control, it will run in a counter-clockwise direction on the example oval.

DCC and non S-9 conforming equipment is a different breed of cat here... For example, Tri-Ang locomotives are wired as such that they run "backwards" compared to S-9 conforming DC equipment.
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Re: Engine polarity

Postby Rob M » Wed Mar 26, 2014 12:03 pm

Perfect, thanks.
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Re: Engine polarity

Postby milwrd1 » Wed Mar 26, 2014 6:29 pm

Yes, the standards state that positive power to the right hand rail should give forward motion so on this loop the engine would run counter clockwise. Assuming, as the Sailor pointed out, the engine is wired in accordance with the standards.
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