Melted axles on Graham Farish N gauge Class 108 DMU

[Simon G]

The MRC that I am a member of has a couple of Graham Farish N gauge class 108 DMUs fitted with DCC chips in both driving car and non driving cars (for the lights on the non driving cars).

 

During use at an exhibition and then at our club Open Day, both trailer cars have suffered from overheating of the plastic axles, which then partially melted the axles making the cars unserviceable. We intend to send these back to Graham Farish for repair, but wondered if anyone has seen a similar problem with their N gauge DMUs?

[Edwin_m]

Have you done the "coin test" on all parts of the layout?  Overload protection should probably be tripping out if something is getting hot enough to melt. 

[34theletterbetweenB&D]

There's plenty of current from even a modest DCC system to make small components hot enough to melt, without tripping the system's short circuit protection.

 

Per post #2 I would want to know how the heat necessary was generated. Top suspicion, some sort of conductive path through what should be the non-conducting split axle element of the wheelset. Conductive lubricant on the plastic or the ends of the half axles not fully insulated from each other, providing a current path with enough impedance to not cause a short circuit, but enough current pasing to generate the heat for melting. With the bogies out of the body, get amn ohmmeter on the damaged wheelsets.

[Simon G]

Thanks for the replies. The layout was being run using either a Hornby elink or Elite and Railmaster.  It has been prone to shorting, so while a rebuild is underway to improve the layout, we plan to address the shorting issue at the same time.  The issue we are concerned with is that only the Class 108s have suffered the melting issue, and we wondered if there was a specific issue with them.

[Simon G]

34's reply arrived just as I was typing my last entry!  I will take a meter to the bogies, hopefully tonight, with the DCC chip disconnected, and see if there is a current leak path across the bogie.

[34theletterbetweenB&D]

As always with a club, it is worth asking questions of whoever has handled or serviced the items in question. Your club may just have' discovered' that this item is allergic to the conductive switch cleaner that one of the members swears by as a general model lubricant, for example. Not saying that's what has happened, just that it is well worth pursuing the local enquiry route as thoroughly as possible, and especially so if no one else has seen the same failure.

[Steven B]

I've seen it happen to a Farish class 47 on a Digitrax system. Potentially the problem with the bogie is such that the short is sufficient to draw enough current to heat the axle enough to melt the bogie, but no enough to trip the short circuit detection on the DCC command station.

 

Happy modelling.

 

Steven B.

[Edwin_m]

I melted a Dapol Voyager a few years back, because I'd been advised to reduce the track voltage and that reduced the short current on the furthest part of the layout to less than would cause a trip.  It derailed such that the left hand wheels of one bogie were in contact with the right hand rail, causing melting around the brass pieces that transfer the current to the chassis.  Not quite sure how this translates into axle damage but may be worth thinking about.