I was afraid of that.
The 400ma limitation is in the Soundtraxx Tsunami documentation pictured here.
How about I hook up the 12V battery directly through a relay in the tender, and I use the DCC function to fire the relay. Does the 12V risk heating up the coils and damaging them? I have some CV boards I could put in there and dial it down to 6V if so. I bought them to run some lights off AC track power, would it hurt to feed them 12V DC and let them output 6V?
I'm thinking of doing a relay to turn on smoke anyway, maybe it's the solution and I can use the same type of relay for both.
CV boards (2 shown)