3-5V High Current 150A Power Supply

[Easy peasy]

there would be a watt or two in the EI lams depending on the flux level you run at (N.B. quality CT's run at very low flux levels - hence their size)

 

[Warpspeed]

This too will run at very low flux levels.

If its designed with enough turns and core cross section to run at 240 volts RMS, running it at (say) 12 volts RMS, both eddy current and hysteresis loss will be extremely low, as will the magnetising current.

The core losses would probably be down in the milliwatt range I would think.

The only real objection to the idea that I can see is the size and weight of the toroidal transformer for what it has to actually do.
But if its free, and we are only building one of these, as an in house calibrator, its not a bad solution.

Once its properly calibrated, only the current in the primary needs to be controlled with current feedback.
There is no mechanism whereby the current transformer ratio can drift or change.

Just a 100mA current shunt to ground in series with the primary (10 ohm resistor) and loop that back to the inverting input of the power amplifier, and that is it !

This naturally assumes a 1,000 turn primary.
But whatever the actual turns ratio turns out to be, its just a simple case of tweaking the current shunt and initial sine wave drive voltage to get the desired 100 Amps.

 

[chinuhark]

Everyone is providing valuable suggestions and I have been absent for a while now.

Well the good thing is that there is some news. Good or bad you guys decide...

I finally did the most basic testing which should have been done several days ago with a variac and a 300/5 CT (this was lying around at our office and all I had to do was put a conductor through it).
It was a 15VA CT.

Good news is that current step up works. Bad news is not very well. I got:

Vprim = 16V
Iprim = 5A
Isec = 60A

The CT saturated surprisingly early. After about 1 - 1.5 Amps, Increasing voltage simply increased primary current and the secondary current refused to increase much. I couldn't exceed 5 Amps primary current as this was the Max rating.

But I'm still not disheartened as I feel that a 1000/5 CT would work even better, much better actually, but I think the best solution will be a 50VA 230V toroidal transformer.

I'm thinking of getting it custom made without any secondary winding (why waste copper right). I'll put a 25sqmm conductor through it. I'll ask the guy to put at least 1000, preferably more, turns in the primary with a current rating of about 200mA just to be safe.

230V rating should ensure that saturation is highly improbable. Now this will be just like the SC test being performed on a simple mains transformer which generally make the rated current flow through their secondaries below 24V (fingers crossed).

Let's see what happens...

 

[Easy peasy]

If you have even the smallest amount of DC (net average DC) in your drive to the CT it will tend to saturate and limit your o/p current - try a big cap in series with the driven side. 1A should net you 60 on a shorted sec for a 300/5 CT.

 

[Warpspeed]

The CT saturated surprisingly early. After about 1 - 1.5 Amps, Increasing voltage simply increased primary current and the secondary current refused to increase much. I couldn't exceed 5 Amps primary current as this was the Max rating..

That has been pretty much my experience with CTs as well.
They do the job they were designed to do very well, but they fall over pretty quickly when you try to push the operating voltage beyond something quite low.

Getting a mains toroid custom wound also gives you the advantage of knowing the exact number of turns.

As Easy P. says, dc is your enemy, but tested with a variac that is not going to be an issue.
Its a potential problem well worth considering later on.

 

[Easy peasy]

A variac should remove almost all of the DC on the mains (due to local loads) but only a surprisingly small amount is needed to saturate a tape wound core (300T) as found on a CT, 1mA = 0.3Aturns, B=uH, = Uo.Ur AT / lm = 10000. 4.pi. E-7. 0.3 / 0.188 = 0.02 T (60mm dia CT core) , so 1mA should be OK, 10mA = 0.2T, and so on... for the AC, a +/- 1T swing in the core would require only +/-50mA thru the 300T winding, so exceeding this will give diminishing returns on the o/p...
if the Ur is higher than 10,000 things will be worse...

 

[Warpspeed]

That is the advantage of starting out with a 240v rated primary.
The original designer probably aimed for perhaps 12,000 gauss for a tape wound toroid, that’s fairly typical.

With only perhaps 12v RMS that shrinks to 600 gauss.
Anyhow, with ac coupling into the power amplifier, there should be absolutely minimal waveform asymmetry or dc offset.