Potential Transformer
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From: Phil Allison on 19 Jan 2006 20:49 "John Larkin" > > Use a resistibe voltage divider. Or a series resistor into a small > audio-type transformer, operated in current mode. Or any ole 240-to-6 > or whatever transformer. You'll probably have to to a phase tweak > somewhere in the system anyhow. ** Using "any ole" transformer is bad advice. Small E core mains transformers have high and non linear magnetising currents - so the output waveform is distorted and does not follow input voltage changes linearly. There is often significant phase shift as well. Small mains toroidal generally have no such issues. .......... Phil
From: John Popelish on 19 Jan 2006 21:33 Phil Allison wrote: > "John Popelish" > > >>If so, you might look at some toroidal transformers with dual primaries >>(115-230). They have quite good voltage regulation under light load. > > > > > ** That last bit looks like a tautology. It is pretty close, as long as the core is no where near saturation. If it is near saturation, a slight change in voltage or frequency can change the input to output ratio. When dealing with instrumentation instead of power transformers, you have to be more flexible with the concept of regulation than just load current regulation. ;-)
From: John Popelish on 19 Jan 2006 21:34 Phil Allison wrote: > "John Larkin" > > >>Use a resistibe voltage divider. Or a series resistor into a small >>audio-type transformer, operated in current mode. Or any ole 240-to-6 >>or whatever transformer. You'll probably have to to a phase tweak >>somewhere in the system anyhow. > > > > ** Using "any ole" transformer is bad advice. > > Small E core mains transformers have high and non linear magnetising > currents - so the output waveform is distorted and does not follow input > voltage changes linearly. There is often significant phase shift as well. > > Small mains toroidal generally have no such issues. Agreed. That is why I offered an example of a toroidal, 50-60 Hz transformer.
From: Phil Allison on 19 Jan 2006 22:06 "John Popelish" > Phil Allison wrote: > >>>If so, you might look at some toroidal transformers with dual primaries >>>(115-230). They have quite good voltage regulation under light load. >> >> >> ** That last bit looks like a tautology. > > > It is pretty close, as long as the core is no where near saturation. If it > is near saturation, a slight change in voltage or frequency can change the > input to output ratio. When dealing with instrumentation instead of power > transformers, you have to be more flexible with the concept of regulation > than just load current regulation. ;-) ** That is purest gobbledegook. The term "voltage regulation" when referring to transformer is related to load. The term you needed and should have used was was " voltage linearity" . ......... Phil
From: Phil Allison on 19 Jan 2006 22:08
"John Popelish" > Phil Allison wrote: >> "John Larkin" >> >> >>>Use a resistibe voltage divider. Or a series resistor into a small >>>audio-type transformer, operated in current mode. Or any ole 240-to-6 >>>or whatever transformer. You'll probably have to to a phase tweak >>>somewhere in the system anyhow. >> >> >> >> ** Using "any ole" transformer is bad advice. >> >> Small E core mains transformers have high and non linear magnetising >> currents - so the output waveform is distorted and does not follow >> input voltage changes linearly. There is often significant phase shift >> as well. >> >> Small mains toroidal generally have no such issues. > > Agreed. That is why I offered an example of a toroidal, 50-60 Hz > transformer. ** Shame you gave a fallacious reason. Good thing the true one is now posted. .......... Phil |