N Scale Controllers

[GreenDiesel]

Long story short, I may have been using controllers that have too high a voltage for N scale. I had been using an older Tech II transformer that has an output of 20VDC and this may have burned out the motors of two of my locos.

I have ultra basic Railpower ones but they have an output of 15VDC -- is that still too high? What transformers would you recommend for N scale? 

I live in Canada but our products should be similar to the US's.

Thanks in advance.

Rob