I NEED HELP (FOR MAKING HIGH POWER TRANSFORMESR!)

Thanks froot , But I don't want to use MOTs anymore , I want to wind up the Transformer that I need , and I need calculations for that , The area of its core , The Number of turns for primary & secondaries and so on FOR MAKING A BOMBARDER NEON TRANSFORMER.

IN FACT I DON'T KNOW ANYTHING ABOUT WINDING A BOBARDER NEON TRANSFORMER (like the one in the picture or ones here http://www.sinolite-neon.com/ProductShow.asp?id=216)!



[Edited on 19-12-2014 by wish i had a kraken!!!]

Quote: Originally posted by IrC

As lacking in knowledge and understanding of the math and theory you appear to be from your own words I suggest you wait a few more years studying and working on things much more safe than your wild dreams. First off you have not stated the voltage and current required. Second you should be talking KVA not kilowatt. If you need an example of the size required I suggest you look at a 10 KVA pole pig up on a pole in your neighborhood. A pole or plate transformer not an NST is what you are talking about at this power level. Gain more experience and tone down your goals for now. Otherwise you will end up as yet another sad story on SCM. I was kind of hoping after Myfawny we would not have any more stories of this nature. Buy a fork lift while your at it a 9 KVA transformer is not what I would term light lifting. Smaller transformers at such a high power level would be meant for very short duration use. Transformers (high voltage) for continuous use require oil filling for both self healing insulation and heat transport. Even at 240 volts you are looking at almost 38 amperes of current being drawn from your outlet, are you really sure you know what you are doing? Are you qualified to be doing it?

Quote: Originally posted by WGTR

One thing that may help is to not make one big transformer, but several smaller ones. The smaller cores will run cooler, all other things being equal. "Transformer temperature rise is directly related to the ratio of transformer surface area to transformer volume; larger cores are thus less efficient in radiating heat losses. For small cores (WaAc < .5) the graphical Po will generate temperature rises <40°C; for large cores (WaAc > 1.0) the graphical Po will generate temperature rises >60°C. " (Power Design, 4.9) In any case, I would suggest starting small, to learn how magnetics "works". This makes small disasters instead of a big ones. Mornhinweg gives a generic set of calculations for power line transformers ("Transformers and coils"). Sources: "Section 4. Power Design." n.d. Lodestone Pacific. Web. 19 Dec 2014. http://www.lodestonepacific.com/distrib/pdfs/Magnetics/Desig... Mornhinweg, Manfred. Transformers and coils. n.d. Web. 19 Dec 2014. http://ludens.cl/Electron/Magnet.html

Quote: Originally posted by jock88

Reminds me of back in the day. The first ever transformer I wound was an (approx.) 10 K Volts out and about 9 KVA. An unruly beast. I HAD NOT GOT A CLUE with hind sight. The input had a variac on it and when taken up to close to 10 KV the output shorted somewhere or other and I had to close things down quick. Then got myself a tank of oil, popped in the transformer and all went well. The transformer needed to be current limited, which it was not. I did not understand what magnetic shunts were all about. Lucky I was not fried alive.

Quote: Originally posted by wish i had a kraken!!!

@ Franklyn, Thanks for your reply to my thread. I have plans to wind up my own transformer capable of providing 9000 volts / 1A . Do you mind if I ask you about the problems I may encounter ?

Quote: Originally posted by jock88

One design item that is very important in large power transformer is their ability to withstand rapid rise or falls in current (caused by say a short circuit). This is something you do not have to worry about as your transformer is relatively small. If large power transformer are short circuited and are not designed for this situation they will destroy themselves by motor action. Forces acting on the coils will cause them to smash. The professional books on transformer design are very involved and take all sorts of things into account like Iron losses, Copper loses (I squared R losses, as they are called) max. temp. rise estimations, what type of Iron laminations you may/could use and a whole lot more. Best approach to take if you just want a relatively small transformer is to take a suitable core area and run from there. The core will already be chosen (from another scrapped transformer) so its a matter of finding out how many 'turns per volt' you have. This can be a very simple formula when things are kept simple and conservative. Then you decide what current density you will work at in the windings. The lower the current density the less heat will be generated and the better the output voltage regulation. Around 3.1 Amps per mm squared is very comfortable. (about 2000 amps per square inch if you are that way inclined). The amount of Copper you are going to wind into the winding must fit into the available space. Not filling all the available space disproves the output voltage regulation somewhat I believe (not a worry in your case). When working with high voltage projects very often you want a transformer with POOR output voltage regulation. Examples are neon sign transformers and microwave oven transformers. These have magnetic shunts placed into the transformer for this function. As more and more current is drawn the output V falls. It is usually OK to short circuit the output without blowing a fuse (or worse). Putting magnetic shunds into E / I shaped laminations is easy enough. I don't know where you would put shunts into C / I shaped laminations. The out winding of high voltage transformers are often pyramid wound and the windings have layers of insulation between them what extend all the way out to the core. Suitable varnish is used too for insulation and holding things together. Remember that with microwave oven transformers the manufacturer knows that the transformer would always have load connected. By knowing this they can be very skimpy with the number in turns on the input coil. If you plug in one of these transformers and do not connect anything to the output for say half an hour the transformer will get very hot (perhaps damage itself) as there are large currents flowing in the primary due to not enough turns in the winding. The beast I spoke of above had a welder transformer as a core. It was around 9KW (AFAIKR). Just over one turn per volt. ie. one turn give (or took if on the primary) just less than one volt. There was something like 15000 turns of enameled copper capable of carrying 300mA at around 3.1 amps per square mm. That is around 4.5VA. All very conservative. It would of course put out far more that 300mA for short periods of time (few amps perhaps). Insulation between each winding was used. It was stuff that consisted of a layer of paper and a layer of clear plastic (don't know what plastic or ratings) stuck together. I believe it's trade name was Elephant Hide! The output winding was also pyramid wound and varnish applies to each winding layer and the layer of insulation 'stuck' on. The windings were separated (on separate bobbins). The primary was the primary that was there in the first place. Old wire that was covered in cloth insulation of some sort (before the days of enameled Copper I guess). The whole lot had to be put into a tank of transformer oil in order to 'put manners on it', as it was doing quite a lot of 'sizzling' when on the bench. The output shorted to the core too but all went well when put onto oil tank. [Edited on 23-12-2014 by jock88]

@ wish i had a kraken!!!

Franklyn I used three MOTs in this way:






[Edited on 25-12-2014 by wish i had a kraken!!!]

Quote: Originally posted by jock88

Remember that the 'usual' domestic microwave oven is rated at about 900 watts but the duty cycle of the oven is low. The manufacturer assumes that the domestic user will not simply run the oven for hours at a time like you would get in a commercial (hotel kitchen say) situation.

Quote: Originally posted by gregxy

When you draw an arc in air, its impedance drops to ~10 ohms. The series resistance of the transformer coils for the MOT secondary is probably >10 ohms.............