On Fri, 30 Aug 2002, Barry Gershenfeld wrote:

>>There is also the way used in some model trains. The voltage is upped for
>>a few milliseconds to change a bistable relay. It could be used by lowering
>>the voltage, f.ex. by having two antiseries zeners shorted by a NC button
>>for ac.
>>
>>Peter
>
>Doesn't the voltage vary quite a bit as the train gets closer and
>further from the feed point?

Yes but they kick the loco with twice the voltage or something like that
(30% more ?), for a few mains periods (it runs on ac, the kick switches a
relay that performs reversing - I think this is the Maerklin system). This
system was invented before semiconductors were available so they had to
use something electromechanical.

Peter

>A while back (1960, Lionel) they actually did superimpose DC onto
>the AC to activate electromagnetics that ignored pure AC.  As I
>recall it sounded the horn.   I also recall that it appeared
>to make the voltage higher.  Maybe this fooled you, too.

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