I see a pretty fair standard of agreement here, to which I would add mine, that 12 volts is plenty as long as there is enough amperage and I agree with 1.5 amps per home set car. Without sufficient amperage, it doesn't matter if 12, 20 or 40 volts are there, the cars won't have sufficient power to perform properly.
Separate supplies to each lane can eliminate inter-car surges but the problem then becomes one of ensuring that each separate power supply produces exactly the same output. Unfortunataly, no matter what is printed on their labels, the true output can vary some. A single good regulated PSU of adequate amperage, eliminates that possibility.
Separate supplies to each lane can eliminate inter-car surges but the problem then becomes one of ensuring that each separate power supply produces exactly the same output. Unfortunataly, no matter what is printed on their labels, the true output can vary some. A single good regulated PSU of adequate amperage, eliminates that possibility.