Tonight, I read the CTI manual and the FAQ and the manual differ in how SmartCAB works. It suggests that the system uses 1 power supply and a 100 step linear switching regulator. All good. The FAQ says it pulses the voltage at low speed, the manual does not say this. Pulseing is a form of PWM. The max voltage is set with a pot on the SmartCAB module. That's a good thing.
There is two heat sinked parts on the module and what looks like a relay. Questions. What are they and what do they do? Relay could change direction. One transistor could be the output device for the variable power supply and the other could be the switch which can pulse the motor. This seems very plausable.
There is an idle voltage adjust. It artificially makes a zero at some other voltage. I BELIEVE it has two functions:
1) Train detection (current in a given section of track indicates train is there) and 2) Could possibly run interior lights or LEDs in the train.
There is a residual 1.2V on the rails at "Zero" throttle. Bridge recifiers located in the train for lighting would null out this 1.2V and with a given zero throttle and a possible switching regulator in the train lights could be illuminated. This is a guess.
It appears it needs current sensing although based on the instructions, you can't set any limits. Short circuit protection is part of a safety aspect. Reversing direction HAS to know when the train has stopped. Thermal protection exists.
The controller has to be aware of current.
I'd love to know what parts are on the board.
This is my SWAG as to what's happening in the controller.
Thus I see two approaches:
#1) Find the power control signal and assume it's a voltage and condition it to run a commercial switchmode PS that is current limited. That's like OUCH! Been there, done that. Make a higher current pulse FET. Find the direction signal and use it to operate a similar higher current relay. Remove the effect of the existing relay. Remove the effect of the existing FET. Feedback the scaled current (significant glue required and isolation probably required [been there]). Advantages: less heat. Disadvantages: relay, some amount of reverse engineering, lots of mods to existing circuit.
#2) High power OP amp with unregulated bipolar rails. Probably custom xformer (been there, done that). Scale SmartCAB output voltage as input to power OP amp. Feedback the scaled current. (significant glue required). Current limit the power OP amp. Advantages: No changes to existing circuit. Disdvantages: OP amp dissapates heat, probably requires fan cooling, noise
In both cases, you could demonstrate proof of concept with 3 Amp rated parts. Some aspects would be the same for #1 and #2.
Questions remain:
1. Which is easier?
2. Which is cheaper?