Most toroids have an efficiency at 96-97% at full load, ie losses is 3-4% of VA rating aproximately, but in Watt. You can check datasheets for X-formers.
90% of the losses is I^2 *R in the windings. Transformers are power limited by their heat loss and temperature increase.
It is fairly safe to assume losses are divided 50/50 by primary / secondary
With the VA rating, and voltage of primary/secondary and some math you can calculate the resistance.
As a note, primary resistance for a 300VA toroid is around 3,5 ohm, a 500VA is around 2 ohm.
That is why you most of the time get away without a soft start for a 300VA toroid, but the 500 VA needs one.
300VA pulls 50-60Amps for one period during power on , worst case, sans charging electrolytes. It works most of the time, pending uF on caps.
500VA pulls over 100 amps for one period. That is enough to trip a 10A fuse in one period.
Adding elytes in a typical cap bank and it is more than one period, and that is definiately an tripping condition.
90% of the losses is I^2 *R in the windings. Transformers are power limited by their heat loss and temperature increase.
It is fairly safe to assume losses are divided 50/50 by primary / secondary
With the VA rating, and voltage of primary/secondary and some math you can calculate the resistance.
As a note, primary resistance for a 300VA toroid is around 3,5 ohm, a 500VA is around 2 ohm.
That is why you most of the time get away without a soft start for a 300VA toroid, but the 500 VA needs one.
300VA pulls 50-60Amps for one period during power on , worst case, sans charging electrolytes. It works most of the time, pending uF on caps.
500VA pulls over 100 amps for one period. That is enough to trip a 10A fuse in one period.
Adding elytes in a typical cap bank and it is more than one period, and that is definiately an tripping condition.
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I decided to use 4 Ohm for the primary and 0.180 Ohm for the secondary.
This gives a reasonable sag of the output voltage.
This gives a reasonable sag of the output voltage.