Can anyone tell me how many amps output in a 100 watt transformer. If it makes any difference its an old american flyer. I want to convert the ac to dc and need to know the amps available. Thanks for any info Franky-Ogee
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Probably you can fairly safely assume you have about 4 amps maximum current from it.
GUNRUNNER; thank you
The 4B and the 8B have 7-15 volt variable posts or 15v fixed and are 100 watt. Which one do you have?
Moonman posted:The 4B and the 8B have 7-15 volt variable posts or 15v fixed and are 100 watt. Which one do you have?
Isn't that 100 watts input, or around 70-75 watts output. Amps output then would be around John's estimate of 4. At least I think that's correct.
The 100W figure is input power, that's how pretty much all older PW transformers were rated. You don't see that kind of power on the output, that's why I go with the 4 amp figure. Could you get 4.5 amps out of it? Probably. However, running the unit at the maximum power output will heat it up significantly. We did a torture test of a Lionel PW-ZW and ran it with 220 watts for over an hour. The temperature inside the case got to 70C, and it was feeling quite warm on the outside! I have a huge wirewound resistor that I can tap to draw various currents to set the power.
Another factor with those transformers, is the rated power is only at full throttle. If you have a variable transformer capable of 80 watts out, for instance, you won't get nearly 80 watts at throttle settings other than maximum voltage. To expect 80 watts out of a 15V transformer at 7.5 volts out would require twice the current, in this case over 10 amps, something to keep in mind.
CAPPILOT,
I agree with your efficiency assumptions, with John's being closer to reality at 40%-60%, but the labeling implies an output capability of 100 watts. It would need a supplied 140 watts to output the 100 watts. They may not have been that efficient.
Todays new labeling with VA is meant for the consumer to estimate it's current usage or the house circuits.
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Where on that label do you see any indication that the 100 watts is output power? Quite frankly, I have one of those here, and with a 6A measured load on it, the voltage was at 10 volts and in a few seconds the breaker tripped. So, mine can't deliver even 90 watts. It was at 12.2 volts with a 4A load. I never saw an old train transformer that was rated on output power, that was sort of a standing joke when you looked at transformer ratings. 
Isn't that how UL defined the labeling?
Yes, the UL labels things with the load that they draw, so consumers can figure out what their usage will be. Like the man said...4 amps available output current.
Thank you gentlemen, I stand corrected.
