Help Need to build a 220/110v 1000w stepdown transformer

Discussion in 'General Electronics Chat' started by born2dive9702, Nov 10, 2013.

  1. born2dive9702

    Thread Starter New Member

    Nov 10, 2013
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    Hello everyone I need some help
    I am an expat living in Italy, and brought some household appliances from the us, forgetting that even with the adapter plug, the voltage is still at 220.

    I dont want to pay $140 for a 1000w step down transformer, I have access to motor wire, and steel. Thus I think it would be cheaper if I built one.

    This is what I need to know
    for a 1000 watt output on the 110v side

    1. what size wire to use for the 220v side of the coil and how many windings.
    2 what size wire to use for the 110 volt side of the coil and how many windings.
    3. what style of Iron core will be the best an E, I, or other style, solid block of metal or laminated and bolted.
    4. stacked coil one on top of the other, or e style.
    5. can i use an appliances ( electric griddle, 800watts, blender, 350watts) that is designed for 110v 60hrz on a 110v 50 hertz system?

    Please let me know
    Thanks
    Brad
     
  2. born2dive9702

    Thread Starter New Member

    Nov 10, 2013
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    Before every one starts warning me about the dangers, I fully understand the dangers.

    I have wired many a home, 220/110 electric motors, generators, and 12 v systems from schematics, I understand HOW to do the job, but not the technical details of why they work. If anyone has a schematic or willing to help please let me know. Thanks
    Brad
     
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    First of all, plain steel is not a very good material to make the core. You need special alloys that have the right magnetic properties and very low conductivity, otherwise you will be losing a few hundred watts in heat in that core.
    Maybe if you really wanted you could buy the materials and make it yourself, but still it will not be as good as professionaly made one.
    I think that biting the bullet and buyinga ready made one is better than doing it yourself and eventually burning your house down.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    To make the core, you need a stack of E- shaped plates of 26-30 gauge silicon steel. Each plate needs to be precision stamped to insure all plates stack perfectly with no air between them. Thinner steel results in less heat loss.

    Before assembling them, you need to dip them in a solution of magnesium methoxide dissolved in methanol, then place in a humidified box and allowed to dry. Repeat that process 30 to 60 times (depending on the surface texture of the silicon steel. This process insures each steel plate is electrically insulated from the previous. Laquer or other paints will work but are generally too thick for a kilowatt transformer.

    Once you identify all the parts and chemicals, let us know, I will help you determine the size of the E- plates.
     
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  5. strantor

    AAC Fanatic!

    Oct 3, 2010
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    How much is your time worth? One Saturday of overtime would buy you a transformer, whereas you will be spending weeks (and probably a lot more than $140 ) to built your own, and in the end it will probably suck hard eggs. You could probably also buy used replacement appliances for cheaper than the transformer.
     
  6. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Given that you need to cut the voltages in half all you need is a a 2:1 ratio autotransformer of 500 VA (Watts).
    Being you are stepping down the voltage on the same winding by tapping in at the mid point the transformer only needs to carry half the power and not the full 1000 watts.

    Easy find online and cost around $50 - $75 if you do your shopping right!

    The easiest way to get one is to buy a common commercial unit with a set of 115/230 windings on its primary or secondary and just use them to get your 2:1 ratio and just leave the other sets of winding leads unused.
     
  7. PackratKing

    Well-Known Member

    Jul 13, 2008
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    There is a way, but it will be the most involved pain-in-the-butt you've ever had, or likely will have... I'll wager a 5% chance of success. :eek:

    Obtain the trans. from an 1800 watt microwave [ overkill ] ... chop all copper / aluminum windings, and start from scratch... The frame E's are the proper grade of steel, already gooped, and welded... disassembly is not an option.

    Then you get to do the math to arrive at proper volts-per-turn, Turns ratios, and phasing.

    Good Luck with that one...:D It is possible... I have done ONE in that manner... Quote the Raven.... " Nevermore " !!!
     
    Last edited: Nov 10, 2013
  8. #12

    Expert

    Nov 30, 2010
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    I have a microwave oven transformer that I use for vacuum tube voltages, and the secondary is completely separate from the primary. That would be an easy one to hack-saw. No, you can't have it.

    Anyway...it all starts with the core. The core has to be large enough to transfer X amount of energy. Then you wind the primary to excite the core properly at the voltage and frequency in the wall outlet. Then you wind the secondary according to the volts and amps you want. That's why you can hack the secondary off and wind your own.

    Good luck and don't forget the rubber hammer. (To make the wire lay down properly as you wind it.)
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you do use a MOT check to see if it has a magnetic shunt in the centre, between primary and secondary, and punch it out if it has one.
    The typical MOT is intended to drive a capacitive load, this shunt increases the leakage inductance of the transformer between the primary and secondary coils and not needed in an inductive load.
    Max.
     
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  10. tcmtech

    Well-Known Member

    Nov 4, 2013
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    The MOT concept would actually work fairly well for building a simple autotransformer from as well.

    All you would need is a pair of matching transformers from 1000+ watt microwaves and use the two primaries in series with the center tap being your 110 volt output.

    Least amount of winding and rework that way. To put the iron cores back together just use some JB weld being it's surprisingly magnetic it works very well as a transformer core epoxy!
     
  11. #12

    Expert

    Nov 30, 2010
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    Put the cores back together? You don't have to take them apart to make an autotransformer out of 2 MOTs...or am I missing something important?

    How about connecting the secondaries to connect the magnetic circuits together?
     
    Last edited: Nov 10, 2013
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  12. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    I think that should work nicely. The only minor obstacles are properly treating the HV connections in order to stay safe, and getting the phasing of the primaries right.
     
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  13. tcmtech

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    Nov 4, 2013
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    Well to me the easiest way to make a pair of MOT into a single center tapped autotransformer would be to take the shunts and secondaries off of one and set the primary from the second MOT in to where they originally sat.

    If done so both sets of windings will be configured a single core and in the correct orientation for them to work in phase with each other.

    By using both original 220 VAC primaries in series the magnetic flux levels in the core will be substantially reduced making for a much more efficient transformer when idle that has a lot of overload capacity!

    Now for putting the cores back together every MOT I have ever taken apart was made with all the 'E' sections as one piece and all the 'I' sections as the other piece with only one thin seam weld on each side holding them together which if a person does not have a welder JB weld epoxy is the next best thing.

    Yea I have repurposed a number of MOT's over the years. :p
     
  14. #12

    Expert

    Nov 30, 2010
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    You certainly have a different opinion from mine!
    Would you please tell how taking both of them apart and re-assembling is some kind of "easy"?

    Yeah, I know, everything is easy, right after you know how. So, do tell!
    Do you need to cut the weld out? How do you get the laminations loose from their nasty-a$$ baked-on coating? Do you need to use an arc welder to put the weld line back when you're done? etc...

    Seriously! School me.
     
  15. tcmtech

    Well-Known Member

    Nov 4, 2013
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    All of the MOT's I have ever taken apart had just those two thin welds which take about 2 minutes with a hacksaw or dremel and cut off wheel to split.

    The cut itself is done right down the middle of the weld so that both laminated sections of the core stay completely together afterwards without problems.

    Once you have a MOT in your hand and see how they are welded together the concept pretty much explains itself. It's really not hard.

    As seen in this picture below there are two welds down each side of the core. The bottom one holds the 'I' sections at the bottom to the 'E' sections in the top. Very few MOT's have their laminations interleaved so that's why cutting two welds allows a complete splitting of the core.

    turn-microwave-oven-transformer-into-high-amperage-metal-melter.w654.jpg
     
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  16. #12

    Expert

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    OK. I don't understand, but the next time I get one I don't need, I'll try it.
     
  17. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Sure.

    As you can see all of the 'E' laminations are on one side with the windings and all of the 'I' laminations make up the end cap.

    Just cutting those two welds lets you change the windings without having to do much work or destroy the core either. ;)

    It think that's why MOTs are so popular for making custom transformers from. They are easy to take apart and put back together without compromising their core design or magnetic efficiency.
     
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  18. PackratKing

    Well-Known Member

    Jul 13, 2008
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    I have several MOT's , and have stripped the copper from a hundred others... The ones that do not have their leaves interlaced, are indeed rare, with taking interlaced units apart being a massive waste of effort.

    On the same note, I would like to throttle the < insert favorite expletive > that conceived the idea of making windings out of aluminum...:mad:
     
    Last edited: Nov 11, 2013
  19. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Could be worse. I got burned on scraping out a number of old Lincoln and Miller industrial 500 - 700+ amp arc welders a number of years ago. Massive transformers with massive windings that looked like regular cooper on the ends where their leads and lugs were soldered on. :D

    All they were was copper clad aluminum which is basically worthless for scrap. :mad::mad::mad:

    My buddy with the big scrap yard got burned on a similar deal as well. They have several semi loads of industrial welders with the same copper clad windings. As far as he is concerned they will sit there forever being they are not worth the labor for stripping for the windings or the steel cores. :mad:
     
    Last edited: Nov 11, 2013
  20. #12

    Expert

    Nov 30, 2010
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    Yep. I have a clothes washer motor in the shed right now, not getting its windings removed because they are copper clad aluminum.
     
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