Hornby R965's in parallel

[Titan]

I have two of these which I wish to run from a single power supply. - Basically the original wall-wart adaptors were not up to the job and overloaded easily. I am actually using them to run some long lego trains. The R965 handles the load OK, and even if they did not they could easily be uprated by simply adding a heatsink to the transistor. So I thought I would replace the wall-warts with a single 16V AC supply from a H&M power pack which can supply up to 2 amps, with the two controllers connected acrosss the 16V AC output.

 

The R965 was chosen as it was a cheap feedback controller and works well enough in that respect - individually powered they work just fine.

 

However they do seem to put a lot of electrical noise on to the 16V AC input - so much so that if you turn the knob on one controller, the train on the other controller will move too, despite the fact that the only connection between the two is via the parallel connection on the 16V AC supply!

 

As the first internal electronics that the 16V AC supply goes through on the R965 is a bridge rectifier, I was rather surprised by that!

 

That also means that they will run off a DC supply, but do they rely on an unsmoothed DC supply to provide a trigger for the PWM signal or otherwise run the electrickery?

 

I am wondering that if I run them off DC with a big enough capacitor across the supply, would that stop one somehow picking up the signal from the other, would it stop them working completely, or is there a better way of running them both from a single power supply?

[kevinlms]

No, its not practical to operate these two controllers off a single AC power supply, as you've already found out! Its because you can get feedback paths.

 

If the wall-wart power packs overheated etc, its because its ratings weren't up to the demands. The solution is to use wall-warts of a higher rating. If the original ones had a rating of say 1 Amp, replace one for one, with a 2 Amp version. It will work perfectly.