[Amps] Transformer surge current

[Will Matney]

All,

Have any of you checked into the surge current of a C-core type transformer compared to an EI type transformer made with Laminations? Have you noticed on a C-core that big thump and hum when powering one up without a surge current resistor inline? What I've been investagating (reading about) is that a C-core does not have a high surge current if hardly any as compared to an EI core of the same size. I was looking this over in a book showing the surge on a scope and it only shows maybe one spike, and that not near as high, in the surge current as compared to an EI over several cycles. The reason for this in their conclusion is the gap in a C-core helps kill it out. There is a way to deal with this in an EI core by stacking part of the satck as a butt joint, and the rest as interleaved. By doing so, it supposed to give the best of both worlds (surge current and saturation). They did some experiments using two toroids, one inside the other making up a whole core. One toroid was gapped, and one wasn't. They fit them together, and encased both with a thin aluminum housing to keep them together. A plastic housing like used now would work the same. I need to investagate this more, but am wondering what your experiences have been between the two?

Best,

Will