View Full Version : Primary Current Draw

03-27-2007, 09:38 AM
The current transformer I have in my HO train throttle power supply has a primary winding of 115 volts.

The secondary is 24 volts with a center tap and is rated at 10 amps.

How do I calculate the current draw on the primary for selecting a fuse?



Robert Kubichek
03-27-2007, 09:58 AM
10amps / (115/24) or 115/24=4.79 10/4.795=2.1

24v 10 amps = 241 watts
115v 2.1 amps = 241 watts

I would go with a 2.5 or 3 amp fuse for primary.
But if you want to protect the transformer,
use a 2 amp fuse and don't draw the full load of 10 amps.

Those transformers are kind of expensive aren't they???


T Chap
03-27-2007, 10:02 AM
Why not meter it?