Ferrite Cores

My ferrite cores are torus in shape, to provide greatest toroid surface area. It almost sounds like you were sold C shape ferrite cores, as most come in torus, C and shell shapes. If you put the two halves, or Cs together, you then arrive at a torus shape – but I can't be for certain yours are C shape because then you mention them as spindles, but then you mention a hole. Sorry I am not picturing it, so this might not be of use to you: how I use them in my old Ham radios and on microphone cabling is to wind the primary around the torus through the hole as many times as I can feed the wire through the hole, and other wire(s) through separate ferrite core toruses. I have to go now and will check post tomorrow, maybe you can take a pic of the core and send then I'll know for sure what you are working with, or maybe someone else wil be joining in and will be able to answer your post.

Here is a picture of the 2 haves. See first post for questions picture is to show what I have.

I have a big stock of ferrite if you are interested please write me at mmoscati@iol.it

I have a big stock of Ferrites

write to mmoscati@iol.it

best regards

Michele Moscati

Do any of these or these or these look like what you have?

I just posted a picture of the pairs look like RM8 accept I have a hole in the center. How do you wind primary/secondary. Join them together. See first question and picture. Never done this before and would like to make a step up transformer similar to the obsolete part made by ON ETD29-3C90 from 12VDC using a switching Fet like MTP6N60E CEMF to 260 VDC to 10uf 450V cap filter to DC for plate of 12AX7 tube. Primary and Secondary tied together in series with switching Fet PWM controller TI494 drives Fet. I have never seen the On transformer obsolete now is there a replacement?

You need a bobbin. Go to some of the links I posted earlier to find one shown.

Ah I was thinking that so do you wind secondary on top of primary? see my first question and please answer what you can? thanks

Now I understand what you've got. I thought you were trying to minimize interference inside your transformer with ferrite, not so. So, as TVP45 said, wind the primary on half coil then secondary. Sounds like a neat project, have fun.

Although you can wind just on a mandrel if you use the buildup like a ball of string (whose name escapes me at the moment), but a plastic bobbin is better to start. Or, you can wind the primary on a half width coil and the secondary ditto. Get hold of a fair-Rite catalogue for ideas.

I have a quick question for you. You asked for the, "equation to go from 12VDC to 220VAC 30ma range." Are you trying to use the transformer to go from DC to AC?

I may be showing my ignorance here, but I've never heard of CEMF switching before. Everything after this might be pointless if the CEMF switching does what I'm about to say...

Transformers only work from AC to AC. There is no such thing as a DC to DC "transformer", if there is please by all means post it! I would love to read up on it. Anyways, to go from DC to AC you could use a PWM and send that through a low pass filter. That should turn the square wave into a sign wave, which could then be passed through a transformer to step up the voltage a bit. The basic equation you could use would be: Vs = Vp*Ns/Np Vs is secondary voltage; Vp is primary voltage; Ns is the number of turns on the secondary; Np is the number of turns on the primary

Hope that helps... If not sorry to waste your time. Please let me know what CEMF switching is!

There is no DC to DC transformer because you would saturate the core in the way a normal transformer works. But a primary "coil" and a "secondary" coil can be used to step up DC voltage. First the CEMF principle. I have one in front of me I designed it uses 6VDC and pumps up a capacitor by switching a HV transistor with a choke 1000uH as the load. I will leave out a lot of theory and talk basic. This circuit uses a 555 multivibrator to drive the HV transistor hard on fast dv/dt to cause the choke to build up a magnetic field. A choke is a coil hooked up to +6VDC and the collector of the transistor. Then turn the transistor off fast the magnetic field has to collapse and when it does the polarity reverses from +- to -+ thus CEMF and you cause a large CEMF voltage spike to occur by causing the magnetic field to collapse quickly which when a magnetic field cuts through the 1000uH coil will generate a higher voltage than 6VDC. The higher voltage is passed through a one direction diode and charges a capacitor. You do this several hundred times a second you will soon see a high voltage across the cap. In my application I use a neon light which with DC will fire at about 90VDC. So when the charge pump reaches the firing threshold of the neon light the light will breakdown and light up and will blink about 1-2 times a second at 6VDC. So we have a DC to DC converter 6V to 90V that causes a neon light to blink at a certain rate. This is CEMF build up a magnetic field in a coil then collapse it.

Think of this circuit as a primary then wind a secondary with more turns with your equation to cause a bigger magnetic field build up and a bigger collapse on the secondary which then goes to a 2nd diode capacitor and pumps this capacitor up to 230VDC. But instead of a choke you are using a transformer with pulsed DC with a very fast dv/dt. So it is a DC-DC converter using a custom wound transformer a ferrite core and you do not need to much current 30 ma would be nice and you filter it. The key part of the circuit is the ferrite transformer step up.

Thanks for the link I am trying to join this group right now.

I think Flyback configuration will convert 12VDC to 220VAC.

Go to the internet and search for "Flyback transformer" and you will find a lot of information.

Comparing those ferrite cores to the penny in the photo, that looks like very little iron for handling power unless you have your 555 screaming right along... significantly higher than 60 Hz.

Bill

I think your talking about my CEMF discussion with another Engineer. You are right the PWM freq is much higher.

Regards.

<< 1.) What is the equation to go from 12VDC to 220VAC >>

It depends on (i) Freq you are working on, (ii) Material of Ferrite, (iii) Single-ended or Pulse or Push-Pull Drive ...

ie In Pulse Tuns ratio is decided on t_o time of circuit; dependent on material & Semiconductors used.

In pushpull it is 1:1 ratio that is P:S = 12:220+ sme extra to meet regulation requirements.

<< 2.) The two halves look identical >>

Bth the wound coils [if wound on separate bobbins in Low voltage output] look identical 7 may be placed on any leg.

But in HV or EHT outputs [like CRT supply] will be Hermatically sealed 7 have a unique look of hard-covering.

It depends on the level of potential in secondary voltage. In EHT [is more than 2KV say ] secondary is wound on separate bobbin & fitted one on each leg for Insulation.

It also helps in rewinding.

<< how do you put the two parts together >>

It is only possible where HV/EHT is not involved.

Two ways:

1.) Have 2 separately wound coils of a little less than half the thickness of Window-Height & put on one of the legs.

2.) Wind Secondary on the same bobbin on which primary is wound. In this cace the total thickness may be a little less than total Window-Height.

Windings are not wound in transformer legs directly but wound on bobbins & fitted afterwars.

<< I have never seen one that is why I am asking. >>

I couldn't understand what you mean.

Have a fine day !!!!!

I have never seen a wound coil means I would like to see a closeup of a wound coil to see how it is constructed and made. I just learned I need a bobbin and I have contacted a company that sells theses. I want to make custom ferrite transformers but I would love for someone to post a picture of one that has been constructed so I can make one like it. I have also learded from a fellow eBay seller that you can make Torroid transformers this sound interesting. Again one nice guy told me about a Nixie Yahoo group and I found a schematic using a 100uH choke and PWM to generate 12VDC to 150-220 VDC @ 50ma 85% efficiency!

Regards.

See custom-transformers

& Search

Google it

Hey Pakistan, I knew a guy from there he was real friendly to me a component Engineer. He would get me free data books. The ref. is LTD sounds like UK. I have tried to buy stuff from one British company and the carriage (shipping) is way to high. Of course what I wanted to buy was heavy also. I buy a lot of my transformers on eBay good deals.

Regards & thanks.

If you can contact any repair shop [not big-fish] & ask for an old [even faulty] PC Power Supply or a monitor [not LCD one] there will be quite a number of Ferrite-core transformers.

Have a fine day !!!!!

I have a big sotck of ferrites epcos

Are you interested?

send me an email mmoscati@iol.it

Thanks for the offer but at this time I want to pursue the ferrite forms I have already bought. Some people are pulling me in all kinds of different directions which is OK put I want to try the ferrite cores I have now as picture is a previous post. Thanks