Eltham Model Railway Club
Ideas and Help - Controllers
At EMRC we use a simple yet effective controller. It is a mechanical/electronic controller. Thay have been used since the club's inception back in 1980.
The controller is a development from kits originally purchased from the Melbourne Model Railway Society and were modified by removing the jug style of element from the circuit and replacing this with series connected diodes. This allows for a smoother operation of locos by varying the voltage rather than the resistance. They have been alway been cheap to construct.
Basically the controller has a mechanical lever that moved a wiper around a circle of bolts which have diodes attached. As you move the controller around the wiper increases the diodes in the circuit.
It relies of the constent electronic charateristics of a normal everyday diode. A diode will always drop the voltage by about .5 of a volt, with dropping the amperage. So our controllers add the diodes into the circuit thereby reducing the voltage down in discrete steps.
Our controllers therefore allow as much amperage yet only control voltage. we find slow speed is quite okay and the system works well with all types of locomotives.
We usually drill 26 holes into plastic or wood - why 26 ? Well with .5 V difference, we need 24 diodes to stop a train. But we also leave one hole for a stop that is not connected to the circuit. We also leave the first bolt the same to allow for a perfect 0V stop.
As we use a spit potential power supply the wiring is ever so easy. Refer to this diagram : This allows us to use three wires in the controller lead.
It's really simple, but here's a explaination on how it works.
- First of all the Power comes via "A" or "A2" depending on the direction switch at "B".
- Next the power passes to the base of the controller's pivot "C" and through the arm. It will then transfer to the boly and thus through all the diodes.
- If the arm is on "E" , there is no power, this the controller is off.
- If the arm is on "F" , there is power, but the power has to pass through all diodes, thus you re at the slowest speed. ( some ultra high motoroed locos , like some portscap locos can move on this setting !
- If the arm is on "G" , there is power, but the power has to pass through all diodes - 1, there is one less diode to pass through and the voltage will be ever so much more ( .5V more)
- So this continues. At the point "H" we are about halfway around and at half throttle.
- When the arm is on "I" we are nio longer going through any diode and thus are suppling full voltage to the track - full speed !
- You notice the 12 V lamp shown at "J". It will provide portection with shorts & overloads.
- Finally, "K" is the track.
You can use this controller on a normally wired system. One bonus is you only need a single diode on the bolts, not one each way.
It is quite simple to make. We use solder lugs that are bolted in to solder the diodes to. The pivot and arm is the biggest challange. That wiper/contactor is the most critical. If it wears it may lose contact with the bolts, causing grief ! There should be sprung, not too tightly so you can use the controller !
