Hello, I've been rebuilding transformers for a friend for some time now and recently got into a discussion about ratings. Postwar Lionel transformers are all rated by wattage between 25 and 275 wats. However, some MPC era transformers are rated in VA. Is this Volt/Amps? Thay range from 7.5 to 25 VA. They put out 16 to 18 volts and run a train set with an engine and 4 or 5 cars just fine. 7.5 VA is generously 6 watts, or is VA some other way Lionel rated these transformers?
Bob
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You'll find that postwar transformers are 'generously' overrated at best.. With a few exceptions, I would not want to run a postwar transformer more than about half its rated capacity for any length of time.. Of course the TW is two separate transformers in one case, so its 'running' capacity would be about 1/4 of the total rated capacity of 175w.. Your mileage may vary.. My $.02..
Postwar transformers were always rated on input power, so if the transformer was 80% efficient, that 275W transformer ended up being really able to deliver 220 watts to the load. Also, that's at full throttle, at lower throttle settings, you won't get anything like that. Imagine expecting 220 watts at 6 volts, that would be over 36 amps! Your 275W ZW has a 15 breaker...
To answer the first question about VA, VA is volt-amps (also called apparent power).
VA = W/PF where PF is the power factor and W is Watts (also called real power).
Power factor is always 1 or less so VA can be equal to or greater than W depending on the equipment.
Full disclosure, I never did well in my EE courses, but can look stuff up on line.
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