Melting axel boxes

[Ian M]

Hi

I thought I'd try out DCC so bought myself a Graham Farrish 3F with a sound chip but the third time I ran it the axel box on the tender melted!  This was with a NCE Powercab.  I assume there was a partial short through the tender axel that was enough to heat up the axel but not enough current to trip the powercab, and as with DCC the power is on all the time with the loco stationary, the heat built up to a point where it deformed the plastic.  No-one down my club has experienced this although I saw something in the recent NGS journal which appeared similar.  Then there are DCC circuit breakers but no-one down my club has seen the need for these? Never had this problem with analogue!  Any thoughts and advice would be appreciated. 

[RBTKraisee]

Sounds like a warranty problem to me.

Ross.

[ntpntpntp]

Never come across the problem other than a second hand wagon with a lighting circuit, where someone had switched one wheel round the other way.

The PowerCab does have an option to show the current draw,  I try and remember to use that when testing a newly acquired DCC loco, just as I use a DC bench power supply with metering when I first test a DC loco.

You have to remember the PowerCab doesn't have a proper built-in overload cut-out, it relies on the power supply.   It probably is wise to fit some sort of breaker or at least the NCE current limiter (which uses car number-plate light bulbs IIRC )

[Safety Engineer]

I had a Dapol Q1 where one of the tender wheels got very warm. Parked it with one wheel just bridging a track insulating joint, resulting short circuit was of a low level not sufficient to trip the overload. Resulting current was enough to heat the wheel up. This was on a DC analogue layout.

[JanW]

The problem is the Powercab, its short circuit protection doesn't work properly.
The Powercab does not shut off track power on a short circuit but it resets because the powersupply is not powerful enough to deliver the trip current.
If it restarts it will restore track power, reset again and this repeats itself, sending current through the loco each time.
I solved this with a DCC concepts PSX1:
https://www.dccconcepts.com/wp-content/uploads/2017/08/DCC-Specialities-PSX.pdf
Another solution is to use a more powerful power supply (2.5A) but somehow people never want to try this (I also tried this and then the short circuit protection of the Powercab works fine).

I still don't understand why the Powercab remains so popular...

Jan

Edit: never use light bulbs to 'limit' current. These will make sure the power will never be cut off sending max current through the loco constantly.
The maths: if you have a 20W bulb on a 12V output there will be a current of 1.7A if a short occurs. The Powercab (or any other dcc system) will not switch off track power which means the 1.7A will flow through the loco constantly.

[martyn]

Rather like post #3, I've seen this twice.

Once, a Dapol Britannia resulted in a melted tender side and chassis on a dcc layout.

The second was a Farish Jubilee on a DC layout, when the loco footplate melted.

The best answer we could come up is similar, that the wheels must have been bridging an isolating break and conducting current, but we never proved it.

Martyn

[Ian M]

Thanks for your replies.  Bachmann have repaired the loco under the warranty and it is now back with me but I'll think I'll be wary of the club Powercab in future.  Still undecided whether my next layout will have a DCC option.

Ian

[Steven B]

I've seen it happen was on DCC with a Farish class 47 running on a Digitrax system.

Personally, I'd be very wary of using any controller (DC or DCC) without some form of short circuit protection. It may not have helped in this case, but I'd certainly be suggesting Ian M's club buys a circuit breaker to go with the Power Cab.



Steven B