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GCA93 8 port current detector with signals


By Peter Giling

GCA93 complete


Current detection is one of the most simple and reliable solutions to detect trains on the track.
This unit is made in such a way, usable for GCA50 / CAN-GC2 / CAN-GC4 connection, and also for others like Märklin S88 system.
Each activated input is indicated by led and separately fused with an automatic reset fuse.
Therefore GCA93 is suitable to be used in systems with powerful boosters.
Without fuses, a short circuit is causing the maximum current, supplied by the booster, through rails, train wheels, and also the input on GCA93 itself.
Serious damage can be the result, including fire hazard.
GCA93 will protect all that, simply by cutting down the current to several milliamps.
The short circuit situation will be indicated, and the occupying signal remains.
After the short circuit has been removed. the fuse will reset itself.
For cost reduction, signals can be omitted. Please refer to Bill of materials.
Omitting the fuses is strongly not recommended, but if it is done, the fuses have to be replaced by a piece or wire.


  • Opto coupler isolation
  • Compatible with MGV50, LocoIO and all other input modules up to 12volt
  • Each input separately fused, to avoid damage to rail or train
  • Fuse will reset itself after problem has vanished
  • Each input has activity indication by Led
  • Each input has fault (fuse active) indication by Led.
  • Adaptable to existing Maerklin contact rails.

Special remarks

If some of your trains are equippped with (self-made) interior led illimination, there could be a small problem.
Specially if you are using central units (e.g. DIgitrax DCS100/200) or boosters(e.g.ORD-3) with regulated and adjustable output.
These units can be selected to G, HO or N scale, meaning output of approx. 18, 15 or 12 V.
Any connection to GCA93 will loose 1.2 Volt inside the GCA93, so for example a HO train made for 15 Volt digital, is now only receiving 13,8 Volt.
That is no problem at all for the train and decoder, you will hardly notice the difference.
But led-chained illumination is sometimes made for voltages up to 18V, meaning that they will not work.
Fot N scale and HO it is not a problem, you simply and safely switch one step higher.
But for G scale that is something you have to consider when you are installing led chains.
Simply calculate the total voltage of all leds of one chain together.
Also consider the rectifier , used for the illumination, because also there you will loose 1,2 Volt in a full bridge.
When GCA93 is used in the configuration from Option 3 or 4 ( see below) the voltage drop is nihil.
A good calculator (unfortunately in Dutch but you will understand it anyway ) for Leds is to be found here:


Connection to rails

1 connection drawing 3 rail system Normal current detection where GCA93 feeds power to the track
2 connection drawing 2 rail system Normal current detection where GCA93 feeds power to the track
3 connection drawing for 3 rail system with contact rails Here, the input reacts on short circuit between two rails
4 connection drawing for 3 rail system with contact rails Same as #3 for long wiring between rails and GCA93

Cable to GCA50 / CAN-GC2 / CAN-GC4

GCA93 pcboard

GCA93 pcboard


No input indication on board :

The board will also work fine without indication.
To cancel indication, omit the following parts:

  • RP1
  • Led1 .. Led16
  • R9 .. R16.
  • D1 .. D8

The circuit works normal but the occupied indication is not visible on the MGV93.

mgv93-en.txt · Last modified: 2022/05/09 22:04 by phg