Hacking an Xray Ferrite Transformer

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Rex Allers
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Hacking an Xray Ferrite Transformer

Post by Rex Allers »

Matt Gibson has a thread about making his own HV supply. A couple months back he posted a link to an ebay seller who had a few Xray ferrite transformers. I got one of them. Matt got two which is all there were (seller had three). Matt has decided to use his in his current supply building thread.

"Matt’s Power Supply Upgrade"
viewtopic.php?t=14515

I haven't tried to use mine in a supply yet, but I have dug into the construction and made a series of measurements. I'm sharing the results here. Hopefully Matt can use the info. For others, they won't be able to get one of these transformers but I hope some might find my discovery process interesting. I'd especially be interested if anyone has an explanation for the intended purpose of one thing I found. There is a copper foil "shield" layer, with a wire out, between the primary and secondary coils. I'm not really sure why.

Here is a picture of the transformer.
xtran_sml.jpg

And this short summary of my key results:
---
Dimensions:
about 4 x 3 x 2 inches

Core:
Ferroxcube UR/70/33/17, Material 3C90

Primary (with the two coils in series) -- 30T
Secondary each coil 900T
Voltage ratio Primary to Secondary 30
---

The details of my process and measurements is in the following pdf file I created.

X-ray Transformer.pdf
(1.45 MiB) Downloaded 306 times

And here is a link to a zipfile with the same pdf and some additional information including pdf's of data sheets for the ferrite core and its material.


http://www.xertech.net/fusor/xray_trans.zip


I welcome and feedback from any readers willing to take the time to read something that may have no direct use to them.
Rex Allers
Matt_Gibson
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Re: Hacking an Xray Ferrite Transformer

Post by Matt_Gibson »

Rex,

This is super helpful!

As for creating the center tap for a full wave multiplier, could the two primaries be connected differently so that the two secondaries can be connected as you had initially thought?

I also wondered about that copper foil piece. I just snipped the wires that connect so as to keep them out of the way.

-Matt
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Finn Hammer
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Re: Hacking an Xray Ferrite Transformer

Post by Finn Hammer »

All,

The foil interleave is an electrostatic shield, and it should be connected to ground.
It's purpose is to block capacitive coupling of high frequency hash from the secondary into the primary coil, from where it could propagate into the electronics of the supply, and cause havoc.

It looks like a really sweet transformer, although it needs to be submerged in oil.

Cheers, Finn Hammer
Matt_Gibson
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Re: Hacking an Xray Ferrite Transformer

Post by Matt_Gibson »

Hi Finn,

Thanks for the info. Looks like I have some work to do getting that shield wire reconnected :-(

Anyways, I got my two transformers wired up (under some oil) and connected to my half bridge, running at 30khz. Seems to be working okay.

-Matt
Matt_Gibson
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Re: Hacking an Xray Ferrite Transformer

Post by Matt_Gibson »

I’ve been playing around with these for a bit. I see that they didn’t come with any spacers/gaps, but I had added some anyways.

I decided to remove them today to see if that made a difference in any way. Well after removing them, the transformers have become pretty noisy. I haven’t yet pushed them harder since I had to remove them from oil to do this and want to let them soak while first. Would this buzzing indicate that they are saturating? I’m running them at 30khz.

-Matt
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Finn Hammer
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Re: Hacking an Xray Ferrite Transformer

Post by Finn Hammer »

Matt,
Saturation in a transformer core is easy to detect. You will need a scope and a current transformer, and this current transformer can well be a simple one, like we use for the feedback in DRSSTC's.
Just a ferrite toroid core with a burden resistor, monitoring the primary current.
Watching the current rise on the scope, you will probably see a sawtooth waveform.
When you crank up the voltage, you may see the current start to increase abruptly at the tip op the tooth, and that is the tell tale of saturation: the permeability of the core material drops to the floor, and the inductance follows, causing the current to sky rocket.
This situation is also a good one to watch why a higher frequency reduces, or even removes the saturation:
Increasing the frequency while the transformer is in saturation, forces the switch to reverse voltage across the primary, _before saturation occours_. Watch it on the scope, and you will never forget
Hope this helps.
Cheers, Finn Hammer
Matt_Gibson
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Re: Hacking an Xray Ferrite Transformer

Post by Matt_Gibson »

Hi Finn,

I let the transformers sit for a bit in the oil and now it’s not making any noise other than the pulsing from the Interruptor that I’m using (for the moment).

I still need to make a current transformer for it since my driver (the UD2.7 from Loneoceans) that I was going to use for an upcoming drsstc project has over current limit functionality, and this might be nice to have in case something goes wrong.

Looks like these two transformers will work well as the base of my power supply. Time to swap my old multiplier board with my new one…Oily mess incoming.

-Matt
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Richard Hull
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Re: Hacking an Xray Ferrite Transformer

Post by Richard Hull »

I have often wondered about sillycon steel laminated 60hz cores and how bumping the drive up to 120 hz or even 1 khz might workout. I imagine there would be horrid core losses in heating. However, such an increase would be nice in a full wave system operated over 1 hour in cooling oil. All one need accept might be a hot core for very intermittent operation and associated gross inefficiency traded for better short term output and net filtered voltage.

So much of transformer design runs through the engineers brain as 100% duty cycle at full design output voltage and current 24-7. Nothing wrong with this thinking if one wishes to keep one's job. Given a .005% duty cycle long term or a 1% duty cycle short term? What might be imagined with extant systems operated far outside there original purpose.

I know from experience that 400hz aircraft transformers run very hot at 60hz if forced to function over long periods. (not enough iron)

Probably has to do with eddy current losses in the thicker laminations on low frequency power transformers. resulting in wasted energy and heating of the core.

The world never had good HF switchers until relatively recently for high voltage, high energy purposes or diodes fast enough to form effective multipliers. The fusor demands both high voltages and high currents compared to what is currently on the market at an affordable price. We kludge up drivers and multipliers and many do it successfully after a period of getting their "sea-legs", blowing up stuff and winding their own HF xfrmrs, working in murky oil baths. But hey, if it works, it plays.

Musing never ceases.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Bob Reite
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Re: Hacking an Xray Ferrite Transformer

Post by Bob Reite »

Worst thing about going up in frequency are the eddy current losses. The laminations would have to be thinner. Practical HF transformers use ferrite cores. which are ceramic compounds of transition metals that are ferrimagnetic but non-conductive.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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