Author Topic: Is my xray transformer a ferrite core and how would I drive it?  (Read 2695 times)

Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #20 on: August 03, 2020, 05:02:26 PM »
Thanks! I wouldn't even have tried without your help!

Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #21 on: August 17, 2020, 11:29:12 PM »
Okay, so the supplier that was going to help me get pictures ended up not sending anything, so I decided to do a teardown myself to see what's inside. Now I found some weird stuff when looking inside.

In the beginning you can see what appears to be 2 smaller flyback transformers. There is also one big round transformer that has a whole bunch of components around it. I had to lift this all by hand so I asked my mom to film it for me so I could look at it after filming, but this made me unable to check where all the cables are wired up.

Which one of these transformers is responsible for the H.V. output and what is the other one for? Is there anything notable in here that could identify what kind of max output is possible with this?

I kind of want to remove the internal capacitors and diodes so I can get a high frequency AC output from it and make it more manageable size wise but I'm hoping you can advice me on if this is a smart idea.

I took the top of it like this for about 5 times exposing the internals to air, is it necessary to pull a vacuum on it now or should it be fine having just been outside of the oil for less then a minute.

I hope my questions make sense, looking forward to a reply  ;D

Offline johnf

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #22 on: August 18, 2020, 10:32:40 AM »
The two smaller transformers are series connected filament transformers to get the required standoff voltage ie one drives the other.
you have taken it out of the oil and also exposed the oil to water laden air.
from what i saw of the bits next to the big ferrite cored transformer are the multiplier stacks.

hope this helps

ps do not drive it anywhere near its max voltage until you revacuum the windings to get the air out

Offline Mads Barnkob

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #23 on: August 18, 2020, 01:11:26 PM »
I agree on the smaller flyback core transformers are the filament transformers.

You can see PCBs with lots of series connection diodes at the end of the large transformer, these form the center-tapped voltage multiplier with the red wires going from the two brown capacitor towers in each side. If you want a AC output, you need to remove the capacitors and diodes.

There certainly is a risk that you now have air bubbles sitting on the underside of things, but you did not have it up long enough for oil to have gotten out of all windings and form air tiny air bubbles without there is still a layer of oil on the parts. Re-vacuum is the only way to be sure.

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Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #24 on: August 18, 2020, 10:22:24 PM »
Thanks yall, that's kind of what I assumed too but there is no visible output for the filament transformer but I guess it's on one of the PCB's.
I am gonna buy a two-stage vacuum pump so I can suck it down. Does it need a deep vacuum? The pump I'm gonna buy is gonna be pretty strong so I imagine I shouldn't go to it's maximum.

Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #25 on: August 19, 2020, 09:04:50 PM »
I ordered the pump and it is rated at around 5pa. I doubt that it really goes that deep but let's hope so I can do some fusion stuff in the future. So my plan is just to run the pump connected to it for around an hour and then disconnect it, is there a risk of the container damaging this way? I imagine because of the oil the compressible air in the systems is just a few liters so I imagine the strain on the container would be pretty minimal.

Offline davekni

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #26 on: August 19, 2020, 09:27:25 PM »
I have no idea if the case can handle vacuum or not, but the remaining amount of air isn't relevant.  During evacuation, you will either have some vacuum space on to of the oil, or you will pump out some of the oil, until pressure reaches your pump's capability.  If the container walls collapse in the process, you will just pump out more oil.

I'd guess that the transformer was originally filled inside a larger vacuum chamber holding the container internally.  Hopefully others here have more specific information.
David Knierim

Offline johnf

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #27 on: August 19, 2020, 09:58:33 PM »
A tank your size would need reinforced sides about 10mm thick or more
if it is not that thick then it is a Dave has said you need a bigger chamber to put it in

I did this with my SEM microscope HV tank after service i used a short length of steel pipe 1m long 900mm in diameter welded end and a flanged top with 20mm plate lid.
has proved to be very useful since vacuum potting transformers de-airing epoxy etc.

Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #28 on: August 20, 2020, 01:27:07 AM »
Hmm, sucks I won't be able to vacuum the whole thing down but I was thinking about getting the transformer out and putting it in a smaller glass container anyways. Now if I went about doing this, would the output side be the center tap of the secondary? Is it easy to wire it up in a glass container like that and does it need grounding anywhere?
I am gonna use a thick solid glass fishbowl so I can pull a vacuum on that and just fill it up with the oil from this tank. Maybe I'll try keeping the rest of the components attached in the original container and I can just use it externally when I need a DC voltage for anything. I hope it's not too hard to remove the transformer but I think I'll manage. I'm thinking about just lifting the whole setup out of the box like I did in the video and place it between some chairs or something more solid so it can lean on that and I can access the components easily. Do any of the other components also require to be vacuumed down? I imagine air doens't trap nearly as much in the voltage multiplier compared to the secondary windings.
Thanks for the detailed responces btw yall. Oh and Johnf, sweet workshop mate  :o

Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #29 on: August 20, 2020, 01:40:10 AM »
Oh and if I use an ungrounded glass container, would that cause dielectric charge buildup on the transformer? Maybe I can partly cover the bottom with aluminium foil and tape that on there with a ground wire to prevent charge buildup on the outside or will discharging it normally by touching the anode and the cathode be enough?

Offline klugesmith

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #30 on: August 20, 2020, 03:34:58 AM »
Not sure about XRT's, but utility transformers with 6-digit voltage ratings generally have tanks reinforced to withstand full vacuum.
I think that's normal for pad-mounted transformers handling only 5-digit voltages, but am not sure about that.
Did you notice any internal reinforcement when you had it open?

Linked document gives a representative procedure:
Close off accessories that are not resistant to full vacuum.
Evacuate main tank without oil, to absolute pressure < 2 mbar.  Hold 12 to 36 hours depending on mfr's requirement.  (In transformer factories sometimes the windings are heated during this phase.)
Admit processed oil from the bottom of tank. (Primary degassing and drying of oil is done outside the main tank.)

https://www.seamarconi.com/en/services/filling-the-transformer-with-oil/

I guess you could experimentally apply a partial vacuum inside your transformer box, and see how it responds.
The flat sides ought to go detectably concave, and you can guess if the amount of distortion is scary.
Not like sphere or cylindrical tanks under external pressure, where failure by buckling can be sudden and dramatic.

Sanity check:  online calculators for deflection of flat plates with uniform loading.  For a box whose edge connections are stiff, I think "fixed edge support" is a better model than "free edge support".  Anyway, a starting point was round plate, 0.3 m diameter, steel 5 mm thick , 100 kPa load pressure. 
Fixed edge:
  center deflection 0.35 mm, max stress 44 MPa according to 2 different sites.
Free edge (an excessively conservative model):
  center deflection 1.4 mm, max stress 111 MPa according to one site.   Not even close to yield stress (~400 MPa), so it will completely spring back when unloaded.
[edit] couldn't keep away.  Here's a ref that says 0.3 m square plate with clamped edges (i.e. corners of box don't act like piano hinges),
only 3 mm thick, could withstand full vacuum with deflection of about 2 mm, and spring all the way back.
https://www.engineersedge.com/material_science/uniform_load_rectangular_plate__13644.htm


« Last Edit: August 20, 2020, 05:49:06 AM by klugesmith »

Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #31 on: August 20, 2020, 12:45:29 PM »
Sadly the inside lacks any reinforcement. I could try tigwelding square support beams all around it but I think this might be a bit too much extra work. I think this container was filled in an external vacuum like davekni proposed as the walls are easily pushed in by hand.
The oil level is very high so if the walls were to all be compressed it would for sure push out the oil from the top.
Now a vacuum chamber that might fit this whole box is just a tad excessive for my needs so that's why I'm looking into using a glass container.
Thanks a lot for the info btw, the procedure that is explained on that link is kind of what I have been looking for but unable to find!

Offline davekni

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #32 on: August 21, 2020, 06:01:44 AM »
Is your glass container designed for vacuum?  Even a thick glass container can be hazardous to evacuate if not intended for vacuum.  Glass is very strong in compression, but weak in expansion.  Vacuum containers are designed to keep all the glass in compression.  Random glass containers, especially with any flat portion, will end up with some glass in expansive tension.  This can lead to implosion failure and likely some shards of glass headed your way at high speed:(
David Knierim

Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #33 on: August 25, 2020, 02:10:20 PM »

Okay, so I got the main transformer out with a lot of effort and now you can easily see where all the wires go. the big brown cables that go around the ferrite are the primary input and the 4 red wires appear to be the output that leads to the capacitor towers but I have no clue which output is which and how to connect them up before relocating to another container. There seem to be 8 very thin brouwn wires going into those PCB's with the diodes so I presume these are the outputs. how would I go about connecting these up to get the highest possible AC output and why do there appear to be 4 primary inputs? Are there also 2 secondaries then?


This image explains the wireing a little bit better

I'm glad I got it out because it's pretty impressive holding such a large flyback
« Last Edit: August 25, 2020, 02:43:19 PM by nielsquake »

Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #34 on: August 25, 2020, 08:45:57 PM »
So I get how this whole rectification process is supposed to work but I can't wrap my head around how to connect the 8 small output wires. I kinda hoped there were just 2 lol but yea. It seems like there are a whole buch of small secondary coils that comprise the whole transformer but I'm honestly not sure. Now I also think there must be 2 primary coils because of the 4 input wires.



In this pic you can see the 4 input wires. I marked the red and blue one as these were working for me to get an output when it was still assembled but I'm pretty sure the other 2 also serve as an input side. Now as you can see in the old pics the transformer had 4 output plugs total and it was advertised to be able to run 2 xray tubes at once so I wonder how this works and how the output is chosen. It also almost looks like the 2 middle wires are connected but I couldn't get a resistance between those 2 so I guess they're not.



Here you can see how the little output wires go from each of these cylinders (I assume are the secondary windings) Each of those coils has only one wire attached and they alternate which side the come out of to the PCB. In this image I've indicated how the 2 wires from 2 of the coils connect to the diodes and which coils connect to which diode PCB. As you can see the coil I've marked with #1 is connected to the right side of the left most PCB and the coil I've marked #2 comes out at the left side of the left most PCB. Keep in mind this pattern repeats like this even though the polarity of the PCB's seem to be alternating in polarity for the diodes so the layout on each PCB and the connection points are the same but the polarity of the diodes is flipped (from left to right +-+-) like a mirror image.



So assuming I'll only use the 2 inputs I marked blue and red. how would I go about soldering the outputs together? or am I thinking about this all wrong? Is it even possible to get AC output from this?
« Last Edit: August 25, 2020, 09:15:06 PM by nielsquake »

Offline SteveN87

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #35 on: August 26, 2020, 11:27:44 AM »
Is that core really ferrite? Looks like it might be Metglas tape:


Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #36 on: August 26, 2020, 01:57:13 PM »
It probably is a tape wound core yea I agree. That doesn't change much about the functionality right?
Is metglas preferable to ferrite when driving the core with high frequency?
« Last Edit: August 26, 2020, 04:42:50 PM by nielsquake »

Offline davekni

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #37 on: August 26, 2020, 06:11:56 PM »
There are several materials used for tape-wound cores.  Metglas is a likely candidate here.  High-frequency performance depends on thickness of the tape as well as material.  Metglas is used up to 20kHz or slightly above.  It can handle higher flux density than ferrite, around 3x saturation flux.  Cure loss gets higher than ferrite as frequency rises.

For large high-voltage transformers, winding capacitance limits upper frequency, so metglas makes sense as a design choice.  Probably ran in the 10-20kHz range.
David Knierim

Offline klugesmith

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #38 on: August 26, 2020, 06:48:14 PM »
Most tape wound transformer cores are made from ordinary silicon steel in strip form.

I think Metglas and other amorphous metals are distingushed by extremely thin laminations (25 um or 0.001 inch).
Their saturation induction is much higher than ferrites, as Dave said, but lower than ordinary steel.

Nice thing about high frequency: you can get plenty of volts per turn without having to push B_max.
But need to mind core loss. Thin laminations or electrical non-conductivity reduce the part from eddy current, not the part from hysteresis.
Maybe not too important in radiography applications, where tube anode heat limits the duty cycle to a few seconds in any 5 minute interval.
« Last Edit: August 26, 2020, 07:03:41 PM by klugesmith »

Offline nielsquake

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #39 on: August 26, 2020, 07:19:11 PM »
Hey thanks for the replies! Before I took it apart the output was pretty good from a 36V lithium battery as seen in this video here
I honestly didn´t know that flybacks were also made of metallic iron too as opposed to ferrite but I was able to run it just like an ordinary flyback with my ZVS driver so that´s cool to know.
I still have no clue how to connect the wires to get AC output though and I still need to find a propper chamber that can handle a vacuum and fit this transformer. I´m thinking about 3d printing a base that fits exactly in the container that fits the transformer so it stands upright in a stable position. Pretty cool idea of having it show in a glass jar just being held at the bottom with the 3D print. I hope someone can assure me that this is possible because I really wasn´t expecting this 8 secondary coil design kind of deal  ???
« Last Edit: August 26, 2020, 07:28:26 PM by nielsquake »

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Re: Is my xray transformer a ferrite core and how would I drive it?
« Reply #39 on: August 26, 2020, 07:19:11 PM »

 


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