[Elecraft] Transformers

[Tom W8JI]

> Well, this is the first time I've had this kind of experience. I'd prefer 
> to know the ac
> voltage of the secondary and make my own calculations, at least with 
> transformers intended
> for DC supplies.

Hi Vic,

The standard practice is to give secondary voltage with a resistive load of 
full rated current.

Sometimes in special applications the dc voltage output with a specific 
rectifier and filter system is given.

The secondary voltage is dependent on turns ratio, load current, and ESR of 
the transformer.  We could calculate the secondary voltage if the 
manufacturer gave ESR, turns ratio, and if we knew load current.

If they gave you open circuit voltage, it still would not tell you dc 
voltage under load or even peak voltage on the secondary under load. All it 
would tell you is zero load current voltage.

Normal industry standard is to give secondary voltage under full rated 
current with a resistive load. This means a 120 volt secondary transformer 
is always more than 120 volts RMS without a load or with a light load. With 
a capacitor input bridge rectifier would provide noticeably less than 1.414 
times 120 volts at rated current because of power factor.

73 Tom