[quote author="mediatechnology"]Right on the money Bob.
In the past we all were freaked out about ground loops and breaking shields without really thinking about where that loop current comes from. It ain't no mystery - it's hum! And what's the source of hum? Power!
I do think matters have gotten worse over time with more and more gear having a proper line filter and loads having greater power factors.
I think you can parallel the secondary windings on the Topaz for true single phase 120V i.e. 120-0 not 120-0-120. Did this at DSL in Irving. What voltage would you be using to feed the primary? 240V? Send me a pic of the Topaz if you can. I've got an old full-line catalog and I'll match pictures. (mediadialupATmindspringDOTcom)
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I'm talking to the "new Topaz" right now to get a schematic. I can psyche it out without them, but it would be real nice to confirm that it really has two independent electrostatic shields as those two wires are not marked. The nameplate is off of this transformer. Maybe that's why I got it for $125!
Anyway, I'll be feeding 220-240 volts to the primary and the secondary I'd like to split that into two split 120 volt secondaries with a grounded neutral. As for "balancing loads" I know it is not fully possible, and with heavily non-linear loads the concept of balancing current is out to lunch. But I do see some potential advantaqe for putting, say, the heavy duty power amplifier on one leg and other equipment on the other. Or, maybe, some of the dirtiest digital gear on one leg and analog gear on the other, thought that gets dicey.
It's not really possible to truely balance your loads. Consider the following example. Two 75W lamp "resistive" loads one on leg A the other Leg B. Now in a 120-0-120 system the vector (and algebraic) sum will be zero in the neutral. So where does the current flow to light the lamps? From leg to leg. Lifting the neutral in this example wouldn't change anything: Both lamps would light and it is still balanced.
I'm not sure I follow you. If one lamp is hooked to one phase's hot and the "neutral", and the other lamp is hooked to the other phase's hot and the neutral, if you lift the neutral wire to either lightbulb, you get nothing, no light! If you lift the central neutral from the transformer, you end up with nothing... So I don't see what you are leading to.
But back to the issue of legs on the transformer. Is it really possible to double up the current by paralleling the two secondaries and having a single phase system?
If you can I would try to make everyting in the room on the same phase 120-0. Just make sure that all of your neutrals are dedicated and home-runned just like iso ground other wise they'll be overloaded. If you can do a 240 primary leg-to-leg you should.
Yes, I'll be doing a 240 primary leg to leg (no neutral involved). On the secondary, I'd like to see some further arguments against using two phases instead of paralleling the secondaries as you are advising. My instincts are two secondaries... not to "balance the loads" per se, but perhaps to have a bit of isolation between the loads.
I know we have three threads going on. I'm trying to pick the thread that's closest to my question so as not to start a fourth!!!
Thanks, all,
BK