Hornby APT (2020 tooling)

[25kV]

1 minute ago, ColinB said:

Oh I thought they were on the lighting. The class 66 did have a batch of capacitors that went short circuit but they were made at least 8 years ago, although I did read of a guy on the Hornby site having the same issue with a class 66. Normally it is tantalums that are the ones that catch fire, why I never worked out. I used to fit them on all my circuit boards as they have a higher resistance than electrolytics but they are expensive so I doubt they would be used in a model railway environment.

Yep - the lighting capacitors (in the 2020 batch) are infamous for being the scale size of giant oil barrels, while the power car capacitors are known for melting the power cars. 

[ColinB]

14 minutes ago, 25kV said:

Yep - the lighting capacitors (in the 2020 batch) are infamous for being the scale size of giant oil barrels, while the power car capacitors are known for melting the power cars. 

Great thank you for the information, that is a lot easier to check.

[ColinB]

Weird, I got the powercar apart and sure enough I found the capacitor. Its weird it was on extremely long leads which sure enough positioned it just below the roof. The one in the class 66 that failed went short circuit but in my case all it did was kill the decoder. I suppose if you were running DC then with maximum current running it could burn out. Anyway I removed it, it is only for TV suppression. 

[spamcan61]

5 hours ago, ColinB said:

 Normally it is tantalums that are the ones that catch fire, why I never worked out. I used to fit them on all my circuit boards as they have a higher resistance than electrolytics but they are expensive so I doubt they would be used in a model railway environment.

You'll still find them on many toy train / decoder PCBs, presumably due to their high capacitance per unit volume. In my day job even 20 years ago we were trying to design them out of telecoms electronics due to their propensity for emitting magic smoke, especially if accidentally reverse biased. You can nowadays get much higher value ceramic capacitors than 20 years ago, so much reduced usage of tantalums, but as I said they still have their uses.