CVT's?

[Osvaldo de Banfield]

Is there anybody here skilled in the art of reckoning or repairing or designing or... CVT's, or ferroresonant stabilizers? I want to stat trying one of such devices, for low power and for may personal use only (not for commercial purposes) I have read some Sola patents from Google patents, but I would want some stuff more specific, with more details if possible.

Many thanks in advance.

 

[indianajo]

I was in a factory that used them to protect microprocessor driven printers. At about 10 years life 24/6 the capacitors on the end get used. New capacitors of those value are probably available; only with a new transformer attached to each pair.
I had another CVT salvaged from telephone service, 48 v , that the transformer had a shorted turn. Hard to tell they run so hot even when new. Took a load test with resistors to prove it. Not going to attempt to rewind it.
CVT were proof against under & overvoltages which on the average don't happen in metropolitan Indiana. What they were really good at was preventing damage from lightning strikes. We have a lot of those here. One took out our main transformer while I worked there.
They are a bit obsolete when the same lightning protection can be achieved with a metal oxide supressor inside a fuse to blow when it fails. Much less wasted energy. Hint, serious motor drives use 21 mm diameter ones with many joules capacity, not the 7 mm ones you find in an PC-ATX switcher supply.
The UPS that replaced the Sola's in the factory had about 3 year life, IMHO. But they were so cheap.
Undervoltage & overvoltage from generator power, can be dealt with by battery charger to inverter arrangements, all solid state.
You're on the coast where the storms come in from sea in the southern hemisphere. I suppose you get a lot of lightning too?

 

[Osvaldo de Banfield]

I had another CVT salvaged from telephone service, 48 v , that the transformer had a shorted turn. Hard to tell they run so hot even when new. Took a load test with resistors to prove it. Not going to attempt to rewind it.

They run hot because part of the core is placed well inside the saturation flux density, helped by the capacitor. Then, yes, high looses in that part of the item. This is how it works.

CVT were proof against under & overvoltages which on the average don't happen in metropolitan Indiana. What they were really good at was preventing damage from lightning strikes. We have a lot of those here. One took out our main transformer while I worked there.
They are a bit obsolete when the same lightning protection can be achieved with a metal oxide supressor inside a fuse to blow when it fails. Much less wasted energy. Hint, serious motor drives use 21 mm diameter ones with many joules capacity, not the 7 mm ones you find in an PC-ATX switcher supply.
The UPS that replaced the Sola's in the factory had about 3 year life, IMHO. But they were so cheap.

I want to start making and testing it, but I have little info or data about them, no more than some US patents.

Undervoltage & overvoltage from generator power, can be dealt with by battery charger to inverter arrangements, all solid state.
You're on the coast where the storms come in from sea in the southern hemisphere. I suppose you get a lot of lightning too?

Certainly not light sticking, but too high dips in the voltages of the net.

Also they have good voltage regulation with no SS, this (probably) will be the PSU for an amplifier under development. I see some battery chargers using the principle of functioning, as they have inherent current limitation and ar shorcircuit proof.

 

[Elvee]

It is yesterday's tech, and there are little details to be found about the implementation because a lot of know-how was necessary above the basic theoretical information, and it was kept more or less confidential because lots of experiments and trial-and errors were necessary to arrive at a workable device: it was a trade secret

Nowadays, with modern design techniques, the design could be much more efficient and deterministic, but nobody is interested in it anymore, because of the poor efficiency.

You could experiment with saturable inductors in LTspice: the advantage is that it costs nothing except your time. When you experiment with real iron and copper, each step is time-consuming and costly.

A good starting point for real tests would be a microwave oven transformer: it already includes the magnetic shunt required (once you arrive at something satisfactory, you can change the turns number) .

SOTA regulators were much more complex than just a transformer and a cap: they were capable of providing their good, pure sinewave output for up to 1 second after the power was interrupted.

I must have documentation about MCB regulators somewhere, but it is in French, and does (of course) not contain any design-usable informations

 

[Vovk Z]

I'm not sure of their very pure efficiency, but the other drawback I think is material consumption - large amount of copper and steel. Modern things, to be sold, have to be made from plastic and only small portion of copper or aluminium.

 

[Elvee]

Here are some details about a state-of-the-art regulator:

 

[indianajo]

I'd ship you the dead 120 in 48 v out constant voltage transformer if you want it and pay costs. About 5 kg. Can still reach it in my scrap pile. Maybe somebody in Argentina can rewind it. Had a 30000 uf capacitor if that tells you anything about current. Output strip #8 screws, not the 5/16" screws used on 50 amp supplies. I used the case as a bicycle battery charger with a regular 44 vac transformer.

 

[Osvaldo de Banfield]

OK, guys, thanks for your suggestions and comments. I will take them into account.