Decoders blowing up?

Nothing is more frustrating than to see a decoder lose its programming or worse get destroyed and blow up in one form or another with smoke.  However not all decoders "blow ups" involve smoke.  Smoke is only the worse senario of the problem.   Many decoder fail in such a way the engine stops running or the engine takes off at full speed with no control.  


What is the source of the problem?

The given layout has an electrical environment involved the wiring and track work such that when there is a short circuit of any kind for the briefest of duration, the electrical voltage level on the track can suddenly jump up to a level that is hazardous to the decoder(s) located near the short circuit.  These are shorts circuits that happen BEFORE the booster can do anything about it.  The source of the voltage is in the wiring and track work itself in the form of electrical properties that ALL electrical conductors have due to the laws of Physics.
  

Why was this not a problem with plain old DC?

Two reasons:

1) No electronics was required to allow a DC locomotive to operate.  In other words, DCC's introduction of a DCC decoder put electronics into an electrically hazardous environment.

2) Operating with a DCC environment, high current (many amps) and constant track voltage, just happens to bring out these wire properties, that were always there even with DC, to new levels where they NOW become a problem.  This is especially true on large layout where the both the wiring and track are long.  To learn more go here: Track & Wire Properties


What is the solution?

1) For existing wired layouts, use a RC filter.  For more information go here: Snubber/RC Filter

2) For new wiring or new construction, twist the track bus wires prior to installation of the bus.  For more information, go here: Twisted Pair Bus Wiring

3) Any combination of #1 and #2 is also acceptable.

The best solution is always to attack the root cause of the problem which is the wiring itself.  The solution involves twisting the track bus wires the go between the booster and the track.  Of course if your installing new track bus wire, twisting the track bus wires together prior to installation makes this a relatively easy solution.  However, most layouts are already wired and are simply being converted from DC to DCC.  For layouts with existing wire, the alternative is simply to "catch" the voltage spike by installing RC filters on the track.  While this is a "band aid" solution, it is very practical and has other benefits in that it cleans up the DCC signal overall due other noise sources which is something twisting the track bus wires cannot address.


Why is this happening to me and not others?

A common reason why some people experience electrical problems and others do not is primarily due to the size and construction of the layout itself with respect to the electrical wiring and track work.  Every layout is as unique as the person who built it in terms of materials used, wiring philosophy, electrical goals, construction quality and finally the size and shape of the layout itself.  Think Fingerprint.   Hence each layout has unique electrical properties in terms of resistance, inductance and capacitance and if some of those properties are not controlled and are too strong (inductance), this can lead to destructive events in the form of a Voltage Spike.


Where is the damage happening in the Decoder?

A decoder consist of many electronic parts called generically "semiconductors".  There is the microprocessor the controls the decoder, the power supply the regulates the voltage going to the processor, the transistor that drive the motor and the transistor that drive the function outputs.  Each semiconductor is specialized to do a specific function.  Together they perform the function of the decoder.  If any of these semiconductors are destroyed, the decoder loses control and/or stops working permanently.


What destroys a semiconductor?

The most destructive and unforgiving electrical parameter of Semiconductors is excessive Voltage.   Semiconductors have absolute maximum voltage limits.  The instant the voltage limit is exceeded, the semiconductor device is destroyed INSTANTLY.  It can happen in a fraction of a second.

A given decoder blowing up is caused by the presence of a high voltage spike that exceeds the voltage ratings of the electronic devices on the decoder.  Frequently it is the motor driver transistors.

Decoders do have some limited over-voltage protection.   However the small version of the devices used (zener diode) have very limited voltage clamping power.  These devices can take the everyday typical voltage spikes encountered.  However, if the voltage spike is strong enough, it can defeat such protection and move on to destroy parts.

It is the strength of the voltage spike that determines the difference between the decoder blowing up and a decoder just losing its programming.


When is the voltage spike created?

Go here: Track & Wire Voltage Spikes/Ringing

How is the voltage spike created?

Go here:  Track & Wire Voltage Spikes/Ringing