Flyback transformers from crts - Page 1
Forum section: electronics / projects

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: August 27, 2017, 04:41:31 am
content: Does anyone know the turns ratio for the old crt flyback transformers and the approximate secondary inductance value I would like to wrap my own custom transformer but can't find the ratio anywhereAnd any advice on where to obtain a core other than an old one or what glue was used in the old ones it's always the color of kapton tapeHow effective is square magnet wire at reducing losses I've been curious about it since I came across it awhile ago

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 27, 2017, 04:52:39 am
content: This is a bad idea, or at least ill-formed, for multiple reasons...I am at least curious how 'old' you're talking -- there were about 3 ages of CRT EHT transformers!Are you after AC or DC?Tim

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: August 27, 2017, 03:26:39 pm
content: Whoops forgot about the different ages of them. regardless of how "dumb" it may be to attempt to wrap my own. I would still like try it .would be not only fun but also practical in my case . I want to build one with an extreme current capitability on the secondary side I have fried many that I pulled from tv's and am tired of that magic smoke we're all familiar with. by the way I'm after AC as I don't want to chop the output waveform .I have done some reading about it from a Texas instruments PDF and will do more. I realize the Gap is a necessary component of the design. I'm just yet to find the turns ratio for it. I'm soon to purchase a cheap winding device to wind it with

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 27, 2017, 08:03:43 pm
content: That's not even a run-on sentence, it's not punctuated at all.That'sreallyhard to read.Tim

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: August 27, 2017, 11:39:00 pm
content: I just modified it I was in a rush earlier sorry

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 28, 2017, 01:03:27 am
content: Ah, well if you want more power, you need a bigger transformer. Which will have a lower self-resonant frequency (maybe 20kHz or less, depending on just how big this is), and a stronger resonance, making a resonant oscillator better than a switching supply.You need tens of thousands of turns to get comparable voltage to an FBT, and each layer needs to be carefully insulated to prevent internal arc-over.Tim

author: Zero999
author_rank: Super Contributor
timestamp: August 28, 2017, 11:53:49 am
content: Quote from: SKHILLBILLYSlures on August 27, 2017, 03:26:39 pmAre you sure it was too much current flowing through the windings which caused it to fail? It's possible the voltage was too high, causing the insulation on the secondary winding to fail short circuit.The greatest challenge to winding your own HV transformer, is adequately insulating the secondary coil.

author: Ian.M
author_rank: Super Contributor
timestamp: August 28, 2017, 03:21:44 pm
content: Quote from: Hero999 on August 28, 2017, 11:53:49 amA typical LOPT EHT secondary has several thousand turns of hair thin wire. Its not even worth trying unless you've got a coil winding lathe + a vacuum chamber and curing oven so you can impregnate the coil with a thermosetting dielectric gel.Even so you'll probably need a multi-section bobbin so you can do a split winding as the volts per turn will be high enough that you will get inter-layer breakdown if you make any section of the coil too wide, and the usual solution of inter-layer tape and margining to reinforce the insulation makes it excessively difficult to get complete impregnation with no voids.You also have to reinforce the insulation for the wire that goes to the bottom of the next bobbin section as it goes past the ends of all the other layers. The best option is a double flange between sections in the bobbin so it can go right to the bottom without contacting the turns in the sections either side of it.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 28, 2017, 03:52:05 pm
content: Winding HV transformers - say, over several kV - is very difficult. BTDT.The internal arcing and/or corona discharging destroys poorly made prototypes in a fewminutesof operation, which is frutstrating, until you get it right. It requires good special materials, vacuum impregnation etc.this is what I built in 2010. IIRC, it tookfouriterations of transformers to get theinsulationright. The first one worked, but only for one minute or so. Finally I ditched the project. (Additional reason it didn't last long was the usage of 555 + CMOS inverter + bootstrap drivers to make the full-bridge signals, which caused a DC offset, with no protection whatsoever. Also see the long wires to the MOSFETs.Most TV flybacks have diodes (+ capacitive doublers) integrated, so you cannot get AC out. This is why I wound my own, completely, because I needed AC.

author: Zero999
author_rank: Super Contributor
timestamp: August 28, 2017, 05:06:44 pm
content: Quote from: Siwastaja on August 28, 2017, 03:52:05 pmYes, I played with that when I was an apprentice. When there wasn't any work on, my boss allowed us to play around with scrap parts in the lab. I tried making my own high voltage flyback transformers from scrap switched mode power supplies but they all arced over. I could get a few of kV from one coil, probably more if I'd used a multisection bobbin but I didn't get that far. When I realised I didn't have the equipment, to do it properly, I gave up. If I wanted to do it seriously, I would simply buy the transformer or even the whole power supply ready made.QuoteThe later TV flybacks do have multipliers and diode integrated, but the older ones don't. Fortunately, I managed to get myself an fairly old flyback transformer for my high voltage experiments. The secondary winding is visible and is wound between layers of Kapton tape, with some kind of wax insulating material to keep the air out. It's also more resistant to over voltage, than the newer flyback transformers, which I believe arced over because the internal voltage multiplier would fail before the windings.

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: August 31, 2017, 09:39:28 am
content: I unfortunately don't know what kind of wax they used on the older ones and will definitely use the double flange construction. What I do have despite my lack of knowledge about the material is "tar" from a busted neon sign transformer and a refrigerator compressor which can be altered to pull a vacuum. I currently lack a chamber. And a understanding of the temp of which the "tar" melts. I am running the current design of this transformer on a ZVS driver circuit with a audio signal imposed on the inductor. I want it loud so current limiting isn't an option and Designing a transformer that can run on several hundred KHz is the only way as it is the quitest arc with and without audio. which the audio signal itself will be hefty in current for sure . I was going to put kapton Tape between each layer and considering doing this between each wrapping which I'm not sure if that is overkill. I would still like to obey the approximate turns ratio of a CRT fly back transformer. but will adjust accordingly to the required impedances on each side. I can't find thermodynamics setting dielectric when I googled it. and where did you get that core you used in the video is made of ferrite as it appears to be?Also doing this at home is going to be hillbilly as hell as I'm going to be using scavenged material mostly and a cheap $50 coil winderPurchased materials include the winder, bobbins if I can find themKapton tape and square magnet wireBut for sure my past use of scavenged flyback transformers has been accepting way to much current into the secondary.Causing the over voltage ZVS drivers are renound for producing such a large arc in the secondary side

author: Etesla
author_rank: Regular Contributor
timestamp: September 04, 2017, 08:01:06 pm
content: I have plenty of experience winding my own HV flyback transformers (5 of them), all of them but one were successful and still function. Here is my method. Step 1.) Make yourself a proper bobbin. The bobbin should be cylindrical and have many (6+) sections. The open areas should have a width of about 1/8" maybe a little less. The walls should be no thinner than 1/16". I find this type of bobbin to be extremely effective for preventing flashovers. It is also very easy to wind. Just throw it in a drill and start it turning until a section is filled with wire, then thread the wire through the slit into the next section and repeat. Generally I use 30 to 42 awg magnet wire. The bobbin is easily turned on a machinist lathe out of delrin with some custom tooling(My preferred method), or could be 3d printed if your printer has filler material options. A couple things to note, The slits should be cut at as extreme an angle as is possible for maximum shielding from one section to the next, and the slits should alternate sides so the first wall has a slit on one side, the next wall has a slit on the opposite side, etc. You should leave a relatively good wall thickness between the wire and the ferrite core, This is where my one transformer failed from flashing to the core. I'm not good with words, so if this is confusing just let my know and I will try to make it less confusing. Also consult the pictures I have attached. Step 2.) Wind the primary, about 6 to 10 turns with an access point in the middle. Step 3.) put the entire transformer in a mason jar filled with mineral oil so that no part of the transformer except the two output wires and the three input wires out of the oil. Step 4.) CRITICAL pull a vacuum on the jar until bubbling has reduced considerably. Step 5.) Light her up!Extra notes on flyback transformers: I had better luck getting good audio out of my lower ratio( lower voltage) flyback transformers, the high ratio ones would snuff out sometimes. With 36 volts input, I get about a 11 cm gap with my highest voltage one (Its really scary), and about a 2 cm gap with my lowest voltage one. I can stretch both of these arcs out further once they are lit, those measurements are just where they gap at. If you are going down the flyback audio path, your in for a treat. I spent about 2 months on flyback before i moved on to coils. Never had much luck with audio while using a zvs rig for power, It was always too quiet even with powerful audio amps powering the audio transformer. I had much, much, much better luck using a tl494 and a single mosfet (irfp260 I think...) Got loud, super clean music out of it using it like a class D at 20 khz:)