Thermister idea

[FJ and G]

OK, so I'm getting dangerous reading up on my Dummy electronics book.

Came across an idea that perhaps we could apply????

Negative or positive temperature coefficient thermisters detect decreases or increases in temperature respectively.

Couldn't a PTC be installed alongside a motor or in a brick to detect when the component is getting to hot and open the circuit?

Just a thought.

[SPFan]

Actually you could use either a NTC or PTC to sense a temperature change and if wired to a comparator could trip a relay to open or close a circuit. Negative or postive temperature coefficients refer to the fact that one increases in resistence to temperature (positive) while a negative coefficient one decreases in resistence.

Pete

[trigtrax]

The thermistor itself would just respond to changing temperature.. You'ld need a trigger circuit to cut power. In the case of shorts and surges the temperature response would be too slow to really protect anything.
One of the features of these newer electronic trains is they are more fragile than the older electromechanical systems they replace. Any protection circuits that really worked would be more costly that the items they protect.

[Anonymous]

Modern thermistors are more designed for voltage compensation in intruments and also transient surge protection. Motors are generally protected by heaters,they heat up and open a circuit which is what a circuit breaker does. Motors on a small scale like toy trains are generally not protected. They rarely burn out and need replacement. The transformer breaker is designed to protected the transformer and the wires but not the engine or cars. Just the same as the breaker panel in your house does not protect a TV set it is plugged into. The TV set itself has fuses in the circuit. This is why I do not think it is a good idea to parallel 2 transformers and run 360 watts through a single track as some do. A short caused by a derailment can act like a miniature arc welding machine on the wheels and track.

Dale Hz

[trigtrax]

The double transformer and other such practices are the result of the different ways toy trains are used today. When I was a kid you got a train set and ran it as it came out of the box.. Maybe you added an operating car or two.. Today's users do lash-up's with several engines and in clubs might run a train with 50 or even 100 cars. The problem is the power required for operation far exceeds what the components can handle when something goes wrong. In addition running under Command Control applies full power to the tracks with the engine electronics used to regulate motor speed. Under these conditions when something fails it fails big time. I've seen plenty of modern engines with cooked boards and the internal wiring fused into one blob of melted insulation.

[lionelsoni]

Dave, your idea has been in use for some years now in power semiconductor devices. The sensor is built right into the chip.