TVS Diode Installation

I use one on each output.  The inputs shouldn't see anything spikey if there are just coming from the power source.  I also put the tvrs on every track feed and in a locomotive if I'm in there working on it.  They have really reduced issues with damage or scrambling of locomotives.  I used to use similar devices on real locos when I was designing electronics for them.  But clamping to 74v for their low voltage control systems.

Matt: Not option A; that will do nothing. For AC power, a bidirectional TVS diode should be wired from hot to common.

The intermittent bouncing contact of a locomotive derailment causes sudden changes in current flow through its motor coils and the coils respond by generating very short yet very high voltage spikes.

I think it makes sense to install TVS diodes right where each motor connects to its driver PCB.

Here's another great explanation on the subject:

https://ogrforum.com/...6#157829273739039876

@Consolidated Leo posted:

Matt: Not option A; that will do nothing. For AC power, a bidirectional TVS diode should be wired from hot to common.

Option A is hot to common on one of the inputs (trucks).

If you're going to the trouble of installing TVS inside the engine (the best place to do so) it makes no sense to add protection to only one pickup and leave the other exposed, assuming the engine has two pickups.

TVS diodes are meant to be installed on the input to short any overages to common and protect the electronics behind the diode. These spikes are generated out on the track so putting them on the output of a source doesn't really do much. Adding a TVS diode at track connections is perhaps the second best place to add TVSs but realize there is still a possibility the engine will see spikes, maybe even from it's own wheels. More diodes around he track are not necessarily better, and can degrade the operation of DCS if you're running that system due to excess capacitance across hot and common.

@turkey_hollow_rr posted:

If you're going to the trouble of installing TVS inside the engine (the best place to do so) it makes no sense to add protection to only one pickup and leave the other exposed, assuming the engine has two pickups.

The two pickups are paralleled at the board in the picture above, so installing the TVS across one is getting both pickups.  Pretty much any locomotive is designed the same way, the two pickups don't go different places.

If this is a TMCC/Legacy locomotive and you also have DCS locomotives running at the same time, consider a 22uh choke in series with the center rail pickup before the TVS.  That will isolate the track DCS from any effect of the TMCC/Legacy electronics and also isolate the capacitance of the TVS diode from affecting the DCS track signal.

@gunrunnerjohn posted:

The two pickups are paralleled at the board in the picture above, so installing the TVS across one is getting both pickups.  Pretty much any locomotive is designed the same way, the two pickups don't go different places.

If this is a TMCC/Legacy locomotive and you also have DCS locomotives running at the same time, consider a 22uh choke in series with the center rail pickup before the TVS.  That will isolate the track DCS from any effect of the TMCC/Legacy electronics and also isolate the capacitance of the TVS diode from affecting the DCS track signal.

I picked up on Matt's comment about only doing one pickup, his option A I think, and just wanted to be sure he did cover both. I am not familiar with connection details so thanks for the education. I should get this done myself as I'm wiring up track.

Well, doing one pickup would not be a good idea if they weren't truly in parallel.  However, due to the short wavelength of the spikes, having the TVS as close to the board as possible is the best method.  In this particular example, being right on a board connector is as good as it gets.

@Matt_GNo27 posted:

Is one of these two options better than the other? Will they provide optimal protection? Or do I need to try to squeeze in two TVS diodes, one for Input 1 and one for Input 2?

One TVS is all that's required, the track connections are parallel on the board.  You can verify that for yourself, just unplug them and measure between the two connectors.