Potential Transformer

If it's isolated from the user, and double insulated, a simple resistive divider may work well.

Why use a voltage transformer if high-value resistors work? just make sure you keep within the power and voltage constraints on the resistors in a resistor divider and you can sample within the range of your A/D converter. Easy!

Is that a request for a 230V to 10V PT? Are you willing to use an ordinary 10 volt step down transformer with a 230 volt primary? Is 9 volts out close enough?

If so, you might look at some toroidal transformers with dual primaries (115-230). They have quite good voltage regulation under light load.

Hello Kit,

Buy them in Europe. Everything is 230V there. You can also buy current transformers (make sure to never, never leave the burden resistors off).

Regards, Joerg

If you want to measure potential, how about a - may I have a drum roll please - voltage divider and ADC?

You _do_ have a common ground reference, haven't you?

Good Luck! Rich

P.S.: Employ me, and I'll help you reassimilate into Real Life. ;-)

** Beware - gmail and Google Groupie !!!

** Where did the "10A" come from ??

Or did you mean to say V ?

A small toroidal transformer would be ideal to derive a scaled and isolated AC supply voltage - but do not use it for powering the device sine the addition of a rectifier circuit will clip the waveform.

........ Phil

"John Popelish"

** That last bit looks like a tautology.

........... Phil

How about a patent on that ?

Graham

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.

Gimmie a resume!

John

"John Larkin"

** 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

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. ;-)

Agreed. That is why I offered an example of a toroidal, 50-60 Hz transformer.

** 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

** Shame you gave a fallacious reason.

Good thing the true one is now posted.

......... Phil

The magnetizing current waveform couples weakly to the secondary voltage waveform. And any electric meter winds up needing some phase tweak somewhere anyhow, as noted.

What makes a toroid different?

John

"John Larkin" "Phil Allison"

** Not true of most small E-cores.

Your knowledge of them is sadly lacking too.

" 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. "

** Not much help when the phase shift is varies with applied voltage. ** Very low Imag when used within ratings.

........ Phil

How many electronic electric meters have you designed and sold? I'm running about 5000 so far.

AC line voltage hardly changes. It's the CT that has the serious phase-versus-current problem, which can be electronically compensated to some extent.

Any core can be run at low Imag. The shape doesn't matter.

John

"John Larkin" "Phil Allison"

** Big noting yourself like this does not work with me.

In fact, it makes you look like a pathetic jerk.

** You are quite wrong, yet again, plus missing the point entirely and as usual.

The point related to using " any ole " transformer".

Remember those words ??

How quickly you do forget.

........ Phil

Why would I care how I look to you? What matters is that the money's still in the bank.

You might be a tad more specific. So how does the shape of the core affect the available Bmax?

Sure. Most any AC power transformer will make a decent PT for metering. Even a little distortion doesn't matter much, if you do the math. Besides, if it's approaching magnetic saturation, and if its primary copper loss is so high that significant secondary distortion results, it will run hot without load. I suppose there may be wall warts this bad, but it would be pretty rate.

And this is a school project... it doesn't have to be qualified to ANSI C12, as my meters were.

John