October 20, 2016 at 2:50 pm #1158
Ch. Zeshan YousafParticipant
Can you use a step down transformer as step up transformer by reversing the primary voltage as a secondary voltage?
If the transformer has two separate windings, then, YES a step-down can be used as a step-up, and vice-versa.
It is more correct to say you are reversing the high and low sides.
By definition Primary is the “IN” side and Secondary is the “OUT” side.
The Primary could be the high voltage side if it is a step-down,
or it could be the low voltage side, if it is a step-up. Design Considerations
Care must be taken when reversing the operation of a step-down transformer to insure that it does not exceed the ratings of the transformer. For example, let’s say we have a 12 VA step-down transformer that takes 120Vac in and is rated to provide 12V at 1 amp at the secondary. If we were to reverse it and apply 12Vac to the new primary (the old secondary), we would have 120Vac at the new secondary, but to keep within the original ratings it could only be loaded to 0.1A @ 120Vac.
As long as you treat the output rating of the step-down transformer as the input rating as a step-up transformer, and don’t try to draw current beyond what would normally have been applied to the high voltage primary, you should be fine. Potentially one could push up the voltage on such a transformer beyond what its stated application specified