What kind of results would one get using a yoke ferite??

[kbeist]

Was just musing about attempting a self wound transformer using CRT yoke split core ferites as the core. Would anyone have an idea as to what I might expect? (Please no coments from the peanutgalery)

I have several sized yokes laying around with about 4 milion miles of magnet wire wound on them. I know what I can do with all that copper, but what if using some of it to make either a low voltage transformer or even a coil for use in a few SMPS's?

Actually it is more like 25 CRT yokes.

Any Ideas??

[johansen]

You can use them for high power, high frequency toroidal transformers. But: they have a permeability of approximately three, the core is designed to spread the flux out through the inside diameter (parallel flux lines) for accurate and predictable deflection. When using them as a transformer, you need to ensure that the turns encompass the entire core or there will be a lot of leakage inductance. here's an example: http://johansense.com/induction_heater/6/P1020794.JPG which is inside this: http://johansense.com/induction_heater/6/P1030090.JPG I haven't measured saturation flux density but you don't really want to be near it anyway because magnetising current will be excessive. realistic limits are in the neighbourhood of a few kilowatts per core at 100khz. 100mT at 100khz should not heat the yoke core up.

[kbeist]

Not an EE nor do I actually know any specs on ferites so please bear with me on this. I am assuming that they are only good for hi-V and hi-Freq then? Or otherwise just a massive electromag? Could you somewhat elaborate on permeability and what its function is within the mag field? (ie. hi perm will render lo inductance?)?

[johansen]

To make this as simple as possible, the magnetizing current (also called no load current) would be [xxx permeability] times higher if you removed the core and attempted to power up the transformer. In real life, if you were to do this with a 60 hz transformer, the wire would light on fire within about 10 seconds to 1 minute. The simple reality is that the core is only there to increase the inductance. For textbook purposes only, it does so by the permeability. (ie, 500-2000 times more than the air coil) The second problem besides low permeability those yoke cores are a rather crappy form factor, they typically have a core area of only 2.5-3.5 cm^2 but the wire has to be 8-10 cm long to wrap all the way around it.

[kbeist]

I thank you for the brief explaination. Perm was the only thing that was my missing link so to speak on what I already know. EI's is what I was taught as both Residential/Commercial Electrician and Naval electronics. But seing as how it has been a number of years since then I have not been able to catch my self up on a few theories of the "newer" technologys. Back then Tandy was still the "in" and MS just released NT3.11.
Digital was starting to emerge out into the real world. I have a good grasp on digital but still lack the "intuit" of puting digital together.
Of course that is all relative now.

[kbeist]

Ok then i'll just the ferite yoke cores. I will probably keep the flyback transformer cores since they take up less storage space and i can Re-use the wire for EI's and it will be at least another year before I even attempt to make a simple SMPS.

[johansen]

if you want to throw all 25 into a 20$ flat rate box i'll take them. Again, due to the permeability of 3 or 4 they are only usable for high power, high frequency transformers.
Alpha cores direct has the cores you're looking for if you want to wind 60hz toroidal transformers. Of course, there's other suppliers as well.

[kbeist]

Thank you for the source reference.
I will definitly send them to ya but I have to unwind them first.
9 of them are ready for unwinding and the others are awaiting complete removal from their original homes (rear projection CRTs). 1 of the 9 is from a Philips 23"-27"ish Flatpanel CRT (rather large) and another of the 9 is from an old Sony Trinitron 15" monitor (lots of wire there). It seems as though the Trinitron's deflection is what gave it its secret display sharpness by increasing the hz scan rate. I have to have at least all CRT TVs by the end of this month. Unwinding will take a while though. I hope you are not in a rush to build anything "Tesla Style". I will send you an email or pm every-so-often to keep you updated on the aprox finish date for mailing your .

[johansen]

You should be able to break the entire assembly away from the CRT. Throw them in a bucket of water, let it all heat up to boiling, then unwind the litz wire, and taking the entire assembly apart is rather easy, for the most part it will all fall apart in your hands. (wear gloves of course.)

I haven't attempted yet to find a solvent that dissolves the glue used to hold the windings together but won't touch the wire insulation, but there's got to be one.

The way they make the crt coils is to coat the wire with glue that melts at something like 120C, then wind the coils on a machine, compress them in a die and heat them to make them stick, this is the reason you can't unwind them, but if you heat them up you'll get litz wire at reasonable quality.. and a lot cheaper than buying it new.

[oughtsix]

Johansen,

What the heck are you building in those photos on your website?