I have been having a lot of problems with the breaker in my postwar 275 watt ZW and KW transformer. I run lionchief plus locomotives with new electronic boards and i don't want anything to get ruined. I have been having some probles with TVS, whenIi put the diode on the ZW, it shorted, the TVS started smoking, and broke in half. I've had some external 8 amp thermal breakers, but they take a few seconds to trip. I did some looking around and found the postwar No. 91 adjustable electromagnetic breaker, I heard that if they are adjusted right, they trip instantly. but Im confused because the maximum a No. 91 can do is 6 amps. but my ZW is 275 watts with a max output of 20 volts. 275 devided by 20 is 13.75 amps. and the KW is 9.5 amps. but the original No. 91 diagram shows the breaker on a zw. so if the breaker maximum is 6 amps, wont the breaker trip as soon as a throttle up? thanks.
Not that Rob needed any verification or backup from me, but he is spot on with his advice. Breakers don't protect train electronics, they protect transformers (and layout wiring, including roller contact wiring in the event of a short.) In particular, I have been using a #91 breaker on a ZW at my test bench for the last 3 years, and among the many shorts I have experienced from defective wiring, crossed leads, alligator clips that accidentally touch, etc., the #91 has performed quickly and flawlessly. More info on the #91 here
The fact that it trips at a maximum of 6 amps is really quite fine, that's more than enough to run most any engine out there, even those with dual motors. If you ran two dual motor PW engines and if you are powering accessories off the same terminal (A, B, C, or D, whichever has a 91 breaker installed), then the breaker would very likely trip under normal running. You should be good to run two or more Lionchief engines since their motors tend to draw less current than a PW Pullmor. They are hard to find used and no longer sold as new, so keep your eyes out on da-bay or at trains shows - expect to pay $20-$70 for a used one. Caution - there is a #91 prewar breaker readily available on the used market - it is not at all the same animal - it is just another thermal breaker with slow response time - probably not what you are looking for.
As you already heard, TVS diodes will protect train electronics from spikes, and are the tool of choice for that purpose since they are quick acting, highly effective and quite cheap. I share Rob's notion that you may not have the correct type of diode installed for it to short on the first power-up like that. There are several you could choose from, but the most commonly refenced is 1.5KE36CA, available from Mouser, Digi-Key, etc.. You might want to check what you used if you have any more to look at (that weren't charred!)
George
