JohnnyDMonic

Just make sure you get an AC -> AC adapter. They can be got in the UK for not much: https://uk.farnell.com/ideal-power/77db-10-09/power-supply-ac-ac-15w-9v-1-1a/dp/2368019

There are a couple of options I can think of without opening up the controller and modifying it: 1. You could try powering it from a lower voltage transformer. Their website suggests 16vAC, so you could try 9v or even 7.5v. You would have to build yourself an earthed metal enclosure with appropriate fuses, etc.. but could be done fairly cheaply (£10 - £20). For example: https://www.rapidonline.com/vigortronix-vtx-126-020-2075-chassis-transformer-230v-20va-7-5v-7-5v-88-3920 (you would have to wire the secondary outputs in parallel.) 2. You could use a variac to lower the mains voltage supplying your existing transformer. This would be more expensive (£60 upwards). For example: https://uk.rs-online.com/web/p/variacs/8902765/ Or, if you aren't fussed about modifying the controller and know a bit about electronics, you could open up the controller and add a resistor in the correct place to form a voltage divider with the existing speed pot. Of course, there's also the good old fashioned method of attaching something to the knob / housing to physically prevent the knob from turning beyond a certain point.

If I were to make another one, I'd be tempted to try a single TIP120 instead of the ZTX450/2N3055 pair. They can be had for a little over 50p.

Hi there Mike, Nice work! A couple of suggestions / observations if I may... You have fitted a 1A thermal cutout device, but your power supply is only rated at 500mA so in the case of a short-circuit the power supply would be running at twice its rated load. There are 2 possible outcomes of this: The first is that the power supply gets very hot and melts / is permanently damaged. The second is that some other protection circuitry within the power supply will kick in at 500mA, rendering your 1A device pointless. I would either beef up the power supply to supply 1A safely, or reduce your thermal cutout device to 500mA. Also, if you put the thermal cutout device straight after the rectifier, it would protect against any other mishaps / failures / short-circuits within the controller itself. If I were building this without using an off-the-shelf power supply, I would probably even go so far as to put the thermal cutout device on the AC side before the rectifier to protect against any failures of the diodes in the rectifier.

Hi there, I am the person who drew that Codar schematic. Please have a look here:

Hi there, I am the person who drew that Codar schematic. It comes from a different forum here: https://forum.allaboutcircuits.com/threads/model-railway-controller.3185/ It was reverse-engineered from a Codar TEC-88 which my dad had since new (see image attachment). It is pretty simple, R2 is the main speed control, R7 is the "simulator" control (basically adjusts the rate of discharge of C1. Switch S1 turns the simulator on/off. I have a feeling I added R3 because I made a copy of this controller for my Dad which had a walkaround remote control. The addition of R3 makes the loco stop if the remote control is unplugged. Either that, or I was adjusting the linearity of the speed pot to make it have more resolution down low. Don't take my word for this, it is just a distant memory from 13 years ago. The copy I made also had a switch to change from un-smoothed DC (how it was on the original) to completely smoothed DC using large filter capacitors (at my Dad's request, for coreless motors). The reversing switch was swapped for a relay with appropriate control circuitry, all to enable it to work from a remote control. I believe I still have the schematic somewhere. If I can dig it out I'll post it up here. For people asking about short-circuit protection, that's what F1 does. It is a poly-fuse (resettable fuse). I believe on my copy there is also a glass fuse on the primary side of the transformer as well.