Short Circuit Protection (Multifunction Decoder)

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Summary: Short Circuit Protection refers to mechanical or electronic means of protecting a device from damage should a Short Circuit occur.

Short Circuit Protection

In a multifunction decoder a mechanical method is not practical. No one wants to disassemble a locomotive to reset a circuit breaker or change a fuse. That leaves electronic methods. The decoder can use two techniques: thermal and current limiting.

Thermal protection means that if a short occurs, the current flow would cause an increase in heat, and when a component gets too hot it can fail. Some ICs are designed with a thermal shutdown system that attempts to protect them from overheating from overloading or a short.

Current limiting is done by monitoring the current flow and preventing it from exceeding a preset limit.

This does not mean that pico fuses are also on the PCB. Blowing those would require a trip to the manufacturer for repair.

The primary defence against short circuit damage would lay with the booster, or a power management device. The second line is good wiring, as a voltage drop drop will increase the current flowing through the circuit. Remember, wiring is important as many boosters rely not on the amount of current, but the rate of change.

Short Circuit Protection in the booster is there to protect the booster!

The secondary defence is check your wiring, and do the initial testing on a programming track which limits the current. Addition of a device such as the PTB-100 by Soundtraxx can also help by identifying a problem.

The most likely cause of a damaged or destroyed decoder is incorrect wiring, where the motor is connected to the frame, shorting the motor drive output to the track.

Further Reading