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Re: [TCML] Variable Inductive Ballast


It may be possible to design a three phase saturable inductor (SR), but a system of that complexity is above my pay grade.

I've never seen a three phase SR for sale, and I've had a standing search for them on eBay for 7 or more years. They don't come up frequently in any sort of incarnation. If such a beast exists, instructions for designing one are probably proprietary to the engineers at transformer builders.

You could certainly use three individual single phase reactors, one on each leg, and drive them from a common control voltage source.

Come to think of it, if you are running three phase input power, that would imply to me that you must be rectifying it and using a DC resonant charged TC system. That would be an entirely different can of worms than a straightforward AC driven TC system that I was referring to. I don't know how a SR would work in a DC system, if at all. I'm not even sure that throttling the primary side of your 3 phases input transformer with a SR would produce the desired level of control after the AC is rectified.

A SR doesn't reduce the voltage output of your power transformer like a Variac does. It just limits the amount of power that can be drawn from the system, by limiting the amount of current available to the primary of the PT.

The DC resonant charging systems that I've seen use gapped inductors between the rectifier output and the gap. Richie Burnett's site in England has extensive info on DC resonant systems. See:


Perhaps you could wind a heavy coil on the center of an E-I core system, and mechanically vary the gap opening with a machine screw. You might even be able to use the original primary winding of a sacrificial industrial power transformer of the appropriate rating, and ignore all of the other windings. If you have access to an industrial water jet cutter, then opening the core to gap it would be straightforward. Otherwise, be prepared to spend a LONG afternoon with a hacksaw and a bottle of liniment.

I suspect that the current setting would be sensitive to tiny changes in the gap spacing, and you would have to have a pretty rigid setup from a mechanical standpoint for reliable operation. All of the gapped inductor systems that I've seen have insulating fish paper or sheet plastic to maintain the gap at a fixed distance. There would be strong electromagnetic forces that would try to pull the gap together as the current in the inductor increases.


On 10/4/2015 11:58 AM, Chris Boden wrote:
This is very interesting stuff. The thing I notice is, does anyone make (or
have detailed instructions on building) a saturable reactor for 3-Phase
power? At 480VAC? I'm really interested in this as a solution. Given the
nature of what we do (and how impressive it is when it goes wrong.....which
happens a lot....) I would much rather use a heavy iron and copper system
than a nice tiny modern silicon system for this application.

Sometimes, low-tech is better. Especially when you make a living by using
products "in a manner inconsistent with its labeling" as our insurance
company likes to say. ;)

Thank you everyone for the replies!

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