LINE----------Com------------->to Topaz
)
)
)
230-------------->to Topaz, 10 amp load (max)
)
LINE----------240
You've got to be a bit careful here. Transformers don't just have one rating, there's a whole family of curves in the A/V plane, of which the "VA rating" is just the headline.So I bought a 250 va "220 to 24" volt transformer at Skycraft as PRR recommended. I discover the primary has both a "240" and a "230" tap. I'd like to try using the primary in "autoformer" mode, tapping into the Topaz on the 230 tap while feeding the line in on the 240 tap. If that brings the secondary of the Topaz closer to 120 volts I'll be more comfortable than the more radical PRR solution. I fear the original PRR solution (using the 24 volt winding as a bucking winding) would take the voltage down too far.
Trying my best to make sure I don't overload anything, it seems to me I calculate the load on the autoformer by the voltage difference times the current.... nominal "10 volts x 10 amps (maximum) = 100 va so that's safe, right? 10 volts comes from the nominal 240 - 230 tap difference.
One more thing: If one of the UPS's doesn't even start at 125V, how could it ever operate when there really is a slight OV problem?
EDIT: BTW I don't think you have stock Topaz from the perspective that it's grey (all the ones I've seen are beige) and most of the ones I worked with for computer/instrumentation use had additional universal taps. This one was probably NASA/Military custom. I don't think it has any bizarre ratios because of that though.
I'd run it in 2.5% step-down. The side effect is that your two internal shields should be switched: the one closer to what you use as primary goes back to the fusebox, the one closer to your working secondary goes to your in-room technical ground. It may make no difference if "wrong", but that's how it should be connected. Primary electrostatic crap drained back to source, leakage from that (and any crap from load) drained to load ground.
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