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GCA78 Contactless ac/dc switching for turnout coil drives

KICAD 3-D The real thing


By Peter Giling

A new approach to control the good-old coildrive for switches

There are several driver boards for switching coils in the GCA assortiment.

  • GCA76
  • GCA77
  • GCA107

They all have their specific functions, but for ac switching only GCA107 was available.
GCA107 is limited to 1 amp for each contact, which can be too short for certain coils, like in Märklin C-type
GCA78 provides 8 switches with a rather new idea.
Solid state relays already exist for a long time, but were pretty expensive, when you
did decide to choose one that is able to switch ac.
Now there is one that is good in price , and also able to switch ac up to a maximum of 2 Amp.
The isolated power to activate each switch, requires less than 7 mA, so it can be used
in direct connection with any of the I/O boards like GCA50(0)(a),CAN-GC2(a), GCA_PI02 or WIO_0(x).

Why is this a better solution, compared to relays?

A switching relay always has the disadvantage of 'contact dender'.
This causes the initial power to the switch motor to be reduced at first switch on,
causing a sometimes weak respond of the switch motor, and that just at the moment that the most power is needed to start the move.
GCA78 does not have that problem, either dc or ac , the internal Fets in the Opto-coulper give maximum power right from the beginning.
Together with the extremely low internal resistance makes this a better solution, compared to the use of a relay.
Practice has proofed, even with dc, that an old fashioned switch motor works more reliable in all situations.


gca78-en.txt · Last modified: 2022/06/12 16:43 by phg