No-Load Output Voltage

The no-load output voltage of an unloaded transformer connected to the rated input voltage and rated frequency is always higher than the rated output voltage (voltage under load). In very small transformers, it can be up to twice the rated voltage. The permissible maximum values are specified in EN 61558 in various “Parts 2-..” and are given there as a percentage of the ratio between no-load voltage and output voltage under load.

Important: Always specify a maximum no-load output voltage when using components whose voltage tolerance could be affected. In such cases, it may be advisable to choose a slightly larger transformer type.

Note: The no-load voltage is especially important when the protective low voltage (max. 50V at no-load) or other voltage limits (e.g., 1100V limit) could be reached.

Hint: The rated values, to which the output voltage tolerance and the no-load deviation refer, apply to the ambient temperature for which the transformer is specified.