Dear all,I have just joined the YMRC and would appreciate some advice on what I am certain is one of those numpty-like queries with a blindingly obvious solution. However, here goes. I have been a `Triang' man since boyhood in the '50s but earlier this year I became a firm fan of Hornby Dublo and have since acquired a small collection of delapidated locos that I am in the process of refurbishing. They are mostly 3-rail and include a few `horseshoe' locos. Having taken a few of the refurbished 3-Rail locos to the local HRCA meetings, I have found that the polarity of the motors is sometimes reversed. I would like to ensure that all my locos run the same way when put on a layout and powered up (space restrictions prevent me from having my own at the moment).  
My first question is what is the normal power supply polarity for 3-rail track? Is the centre rail +ve or -ve? 
My second question concerns the polarity of the H-D `upright' motors? I have several locos as yet untouched by me however, when I tested their field orientation with a compass, most showed `North' to the left of the ahead position but some showed 'South'. I would have expected the same compass orientation to be necessary to ensure consistent direction of travel when run on any given powered test track. If I'm right, which way should the compass show `North' to left or right of the ahead direction?
All help, advice or even insults are welcomed!

Chris, I am sure someone in Home  On-line Forum will be better able to answer your questions.

Hello Chris and welcome. I should imagine there will be someone on here that can help you or point you in the right direction. Good luck.

Hi Chris

I would imagine at some point inn their life these locos have had some work carried out on the motor and the wires to the motor's brushes have re-attached the wrong way round.

It is a fairly straight forward job though you will need a soldering iron, solder a pair of thin nose pliers and possibly a short length of wire. Basically remove the loco body locate the motor and you will the commutator above the winds of the motor at either side is a carbon bush and attched to that is a wire and a small electrical component (a capacitor to reduce radio interference). You just have to change the 2 wires over you may have to extend them if they are to short.

Test the chassis on the track to check the loco works and and runs in the right direction.

Good Luck

Nigel

I've never ever had anything to do with 3 rail but my "mental reasoning" would suggest that the idea was to use the centre rail as the +ve and return through the outer rails.  On Trix stuff (I was once given a Trix loco in a box of other items), and maybe also on Hornby Dublo, the pickups were sprung tabs under the centre of the loco with a very easy return via the chassis and wheels.  This kept the need for insulation to a minimum.

It would therefore, seem strange that someone who knew what he was doing, would re-wire the motors with reversed polarity.  They could have been "messed with" by someone trying to convert them to 2 rail operation, deciding it was either too difficult or rather pointless, so he just slapped the wires back on willy-nilly.

Is there any sign on the brush holders of a re-soldering job Chris ?

Hi,
I agree that logic suggests the centre rail should be the +ve feed and since accumulating an assortment of dublo locos, have been working on that basis. I did once install a neomagnet the `wrong way round' only to discover this when I placed the loco on a fellow member's track and it went backwards under forward control. Since then I have been working on a number of locos & motorised chassis acquired through ebay and have been checking the magnet polarity of each in turn. The majority are post-horseshoe motors and show the compass same side of the direction of forward travel, however the horseshoe ones are a mixed bunch. One reads north to the left whilst the other two read north to the right. The wiring to the brushes of these horseshoe chassis is the identical so I'm now wondering if previous owners have removed these magnets and reversed them when replacing.  What I'd really like to find out is the original factory set-up and make sure my rebuilds follow that.