Ferrite ID

David Lesher 6 hours ago

Rheem tankless water heaters, fed with dual 40A 240V circuits, are driving all the Leviton and other brand dimmers berserk. The lighting all dims and flickers beserkly. The Rheem has a sharp spike at the peaks of the positive and negative cycles; that is the cause.

The cure is some ferrite chokes on the power feeds. But fields class was Many Decades ago. I'm trying to decide if I want ones with an ID that just accepts the #8 stranded, or it doesn't matter that much if it's a loose fit.

Thoughts?

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John R Walliker 6 hours ago

A reasonably tight fit gives better results, as does using a ferrite tube rather than a short bead. However, if its a loose fit you may be able to feed multiple turns through it which works well at lower freequencies. The material does make a difference too, according to the frequency range you are trying to absorb. John

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Bill Sloman 5 hours ago

RM ferrite cores are available in a fair range of sizes.

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Here the data sheet for the TDK RM10 core taken from that site.

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You'd buy two RM10 (or whatever) core pairs, wrap the power lead around the central pole of one half of the pair, clamp the other half on top and use a pair of spring clips (B65814B2203X000) to hold them together.

Broad-line distributors tend to stock them, but they rarely have the whole range.

Bigger cores go up to RM14 and you might be able to pack in a couple of turns of power lead. RM4 is the smallest, and probably too small for the application.

A single turn around an RM10 core is worth about 5uH (from 1.6uhH to

16uH) depending on the ferrite. It goes up as square of the number of turns.

If you dig into the application notes you can find out about magnetic saturation.

You were probably thinking about ferrite beads/ferrite tubes, but they tend to be a bit idiosyncratic.

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