Romero's experiments and OU principles

[teslaalset]

No im generalising without going into exotic iron mix like carbonyl iron with ceramics can run to a Ghz. But in practical terms anything over a couple of megs  is already heading towards air cores. As Ismael uses Tesla bifilar Air-Cores for his MEG.

Wiki

"Iron Powdered cores made of hydrogen reduced iron have higher permeability but lower Q. They are used mostly for electromagnetic interference filters and low-frequency chokes, mainly in switched-mode power supplies.
[edit]Ferrite
Main article: Ferrite (magnet)
Ferrite ceramics are used for high-frequency applications. The ferrite materials can be engineered with a wide range of parameters. As ceramics, they are essentially insulators, which prevents eddy currents, although losses such as hysteresis losses can still occur.

So unless you have an incredibly fast rotor its probably going to work better  with iron powder while the old AM LW MW radios used ferrite rods, slugs and cores for these frequencies and certainly not iron powder.

Mu-metal is pretty powerful stuff and as romero said VERY expensive. Don Smith used a lot of Mu-metal as well as another type which is around 10 times the cost of Mu-metal i cant think of the name right now,  Mu-metal has  permeabilities of 80,000â€"100,000. There is a trade off for materials there is no point making a 15 watt OU device that will take 200 years to pay for itself:)

Ok, thanks for elaborating a bit on that, although I prefer real data instead of Wiki stuff, I've used iron powder cores at pretty high frequencies myself (e.g. Bob Boyce hex controlled iron powder core )

For now, I think we better stick to ferrite and try to replicate what has been shown, before going into exotic materials without necessity.

[bolt]

Romero
have you tried what same type core material that John B
used?
welding rods
KC

Welding rods are a real terrible hack! They provide a little extra  inductance  suitable for only very low switching speeds. <20Hz They make work fine for bedini bicycle wheels spinning a couple hundred RPM but any higher the eddy losses are chronic.  Get decent cores suitable for the job.

[romerouk]

I have used welding rods for some of the Bedini as probably many others here, but tried and used different materials too.
Below is a circuit diagram I modified and used recently.

[Mk1]

Dose it really speed up , or is it just the core drag that is eliminated ?

[neptune]

@Romerouk . You speak of using iron dust cores . Does this iron dust come as a powder , or in a solid form . Also have you tried Iron oxide [Fe3o4] please ?