= Rsecondary
+ Rprimary * [Vsecondary {unloaded}/Vprimary]^2
You'll also have to be very very carefull and measure the unloaded secondary voltage.
Or set V secondary unloaded
= Vsecondary rated
+ I rated * effective DCR used for secondary in PSUD II
and ignore the difference between Vsecondary unloaded and loaded in calculating the effective DCR.
Example:
Vrated secondary 230V rms
Vrated primary 115V rms
DCR secondary 100 ohm
DCR primary 20 ohm
Irated secondary 200 mA
DCR for PSUD II = 100 + 20 * (230/115)^2 = 180 ohm
Vsecondary for PSUD II = 230V + 180 ohm * 200 mA = 266V
(When checked
[115V - 20 ohm*0.2A*266/115]*266/115-{100 ohm*.2A) = 224.6V loaded
for 5.4V error out of 230V)
If you want, you can iterate a couple times to get a better value, personally, I wouldn't. But for perverse curiosity I'll do one iteration:
DCR pass 2 = 100 + 20 * (266/115)^2 = 207 ohms
Vsec pass 2 = 230V + 207 ohm * 200 mA = 271V
(When checked
[115V - 20 ohm*0.2A*271/115]*271/115-{100 ohm*.2A) = 228.8V loaded
for 1.2V error out of 230V)
Play safe and play longer! Don't be an "OUCH!" casualty.
Unplug it, discharge it and measure it (twice) before you touch it.
. . .Oh!. . .Remember: Modifying things voids their warranty.