GeoPeg posted:I can think of two reasons why a 40 amp diode was specified. The first is simple; bigger is better - or stated in other terms, overkill is better than not enough.
The other reason might be to handle a dead short that could occur just as you are blowing the whistle. I stole the following explanation from LIONELSLONI :
When you work the whistle control, it first replaces the direct connection from the roller with the 5-volt winding in series with the rectifier. This gives a strong DC voltage intended to operate the whistle relay. But the motor will slow down. Then, as you move the control farther, it should connect a 1.5 ohm resistor in parallel with the rectifier to get the voltage back up to a reasonable level, with only a small DC component to keep the relay closed. If you work the control quickly enough, the train will not have enough time to slow down while the control is in transition.
So for that brief instant before the 1.5 ohm resistor is hooked in parallel with the diode, it is possible to dump all of the ZW's 14 amps directly through your diode. That could be an issue I think, for an 8 amp diode.
That's a great explanation; there's more going on behind the whistle control than I realized. Thank you for sharing that. Also I was looking around but couldn't find a chart that shows the maximum current the various transformers put out. Good to know the ZW is 14A.
I once read on this forum that the ZW can weld into a dead short before the old thermal breaker kicked in...I have some 1122 switches from 30 years ago to prove that! (geez, 30 years ago seems like a long time ago, but then to realize that was in the mid-1980's which doesn't seem long ago at all...but I digress...)
Well, I just received two 1N1190AR's in the mail so my next project is to install them in the ZW. I can re-use the 45V/8A diodes in my 1033 and RW transformers.
Roger
