Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Building a transformer.

  1. May 23, 2005 #1
    For my project I need to transform the power from a 3000 watt, 120V AC generator to a high voltage DC, say 30,000V DC.
    Are such transformers easily made or of low cost?

    Bob Clark
  2. jcsd
  3. May 23, 2005 #2


    User Avatar
    Science Advisor

  4. May 23, 2005 #3
    Monitors and televisions also have transformers that develop voltage in that scale ~15-35KVdc
  5. May 23, 2005 #4
    Thanks. But could they handle high wattage like 3000 watts?

    Bob Clark
  6. May 23, 2005 #5
    This looks like it's only for creating long sparks. I want to generate continuous high voltage DC.

    Bob Clark
  7. May 23, 2005 #6


    User Avatar

    Staff: Mentor

    You want 3000w output? You'll lose an enormous amount of energy in the conversion (I think). What are you trying to do this for?
  8. May 23, 2005 #7
    Yes I want 3000 watts in the output. If I lose some amount in the conversion that's OK. I just use a larger input.
    What I want to do is build a high thrust "lifter" device. The lifters built so far have lifted some few grams. I want to lift kilos.
    Here is a page discussing the lifter devices:

    The Lifters Experiments home page by Jean-Louis Naudin.
    http://jnaudin.free.fr/lifters*/main.htm [Broken]

    I can do the change from AC to DC with a rectifier (actually the lifters can even work with AC so I might not need that.) The main problem is raising the voltage from 120V AC to 30,000V AC with a transformer when the electrical power is in the 3000 watt range.
    I know power companies do this in both directions all the time. What I want is a low cost transformer that can do this or be able to build one on my own.

    Last edited by a moderator: May 2, 2017
  9. May 24, 2005 #8


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    "Low cost?" "3kW?" "30kV?" You can have two of the three --- although "low cost" at 30 kV ain't all that low.
  10. May 24, 2005 #9
    This bbs is doing that weird thing of putting extraneous asterisks in URL's again. When you click on the link for the lifters experiments page, if it doesn't open because there is that asterisk inserted in the address bar, just backspace over the asterisk and reload the page.

    What I wanted to do was encourage extending the work done by amateurs with lifters to the kilowatts of power range. However, I am informed that
    using high voltages while at the same time having high wattage means
    the amperage would also be high. This can potentially be lethal.
    There are relatively inexpensive ways of transforming the low voltage
    put out by electrical generators to the tens of thousands of volts you
    need for the lifters. If you have experience working with high voltage
    and amperage, then you already know what they are.
    It should not be attempted unless you are already well experienced
    with working on and in high power electrical supplies.

    Bob Clark
  11. May 29, 2005 #10
    You have a bridge rectifier that can handle 30 kV at 3 kW??

    Really? I don't think that would work.

    Yeah, you should probably ask the power company. :-)
  12. Jun 29, 2005 #11
    The first step in your research is to investigate high wattage / high voltage transformers. These present special problems, like insulating the coils!

    Such transformers have been actually designed and used in military equipment for radio transmitters and RADAR. I noticed you said 120 VAC but you didn't specify the frequency of the power source. That is okay, but high frequencies present another technical hurdle. (none of these factors help cost, although you can make the transformer yourself.)

    If you are thinking of doing this and want to overcome the problem of finding an 'off the shelf' xformer, you can always connect the secondaries of a large set of xformers in series: Here you have to be very careful (there are serious special precautions needed), since there are technical problems and dangers in handling the resultant high voltages, and also in preventing the failure of one component causing a catastrophe.

    Look into older Ham radio transmitter designs for ideas on power output transformer requirements, especially commercial radio station equipment.

    Like others before you, you will discover that you will have to resort to 'tubes' for the power rectifiers, not semi-conductors. Even here, the incredible voltages you want need special circuit designs. I recently doubled the high voltage in a tube circuit in order to achieve other design goals: even this little jump in voltage (450 v to 1000 v) required serious precautions and careful design to avoid dangerous conditions in case of small part failures like resistors and capacitors.

    Normally, people don't even think about the 'voltage' rating of a resistor, but in this case its real and very important that you don't exceed sensible limits. Capacitors are particularly sensitive to surge-voltages and high-tension.
    Last edited: Jun 29, 2005
  13. Jul 2, 2005 #12

    This lifter thing just looks like the action of ions under high voltage. I have felt the "wind" caused by such a near discharge. It is very weak, uses small current, and is strictly conventional physics. In my case I used two needles or a needle and a wire ring. Anything over 20KV would be fine. Low current is preferred so you won't get shocked too bad if there is a mistake. It would be difficult to make a vehicle using this method for lift and I doubt if it would be able to leave the atmosphere.
  14. Jul 10, 2005 #13
    There is a NASA page discussing their work with this sort of thing. They covered it fairly thoroughly back in the 60's and early 70's.
    The lifter does indeed work by íon wind' they conclude. It will not work ín vacua' - every experiment to try this shows it doesnt. 30Kv is a very modest performance for even the smallest of Tesla coils, but that's high frequency AC. The DC requirement is met by joining the top of the TC to your apparatus (effectively another capacitor) with a wire of high resistance. The current flow from one plate of a capacitor to another when joined by a high resistance is unidirectional - DC in other words. Your challenge is to find a substance that does not behave like a conductor at TC frequencies... Perhaps you might find a simple Van Der Graaf generator easier. The smallest output would be about 100Kv from an elastic band and a couple of empty coffee tins (my 10 y.o. son built one -they're easy)
    So, Voltage is not nearly the problem you think it may be.. getting that voltage at the power you ask, and having it be a DC current - cheaply? easily? Sorry. Only by lots of work or lots of dollars..
  15. Jul 10, 2005 #14
    Not to mention that it could be brought down super easily by just shorting out the conductors. It only creates ion wind when there's a corona; not an arc.

    Why do you want that much current, anyway?
  16. Jan 20, 2008 #15
    Building a transformer

    You should try to scale back your experiment. There is no practical use for a lifter with that power. Also, at that high current, it would probably catch your wood frame on fire when it carbon tracked. I recommend you use a neon sign transformer. These come in all varieties and are usually cheap or free. I would advise a 15kv 450va one. Then you can use a Crockroft-Walton voltage multiplier to raise your voltage and convert to DC. Also, these multipliers generate pulse power and are excellent for lifters (I have used them before). In addition, these transformers are safer than the 3kva type you are talking about. Don't use a Tesla coil as these are not used for (relatively) low voltages such as 30kv. Most Tesla coils generate well over 200kv. While Tesla coils do generate excessive corona, they are expensive, tempermental, and require lost of time. If you are really set on the 3kva figure, okay, what you need here is a pole pig. These are the transformers you see on top of power lines. They come in all sizes with 5kva being the smallest common size and secondary voltages being around 14kv usually, but you should be able to find one which can handle 30kv@3kva. Most pigs have a 240v primary so you will need 3kva transformer to step up your 120v supply to achieve the high voltage. Also, you will need a ballast to limit the current the pig can pull. These transformers are not current limited so, they can explode if you short it and it can get more than its rated current. A ballast can be made simply. Search google. Finally, you will need a high voltage rectifier. Search around on Google. These require high voltage diodes which are fairly expensive. Another route to go is a padmount transformer as these can sometimes handle higher voltages, but they are heavy and require more power to justify the cost. Unfortunately, there is no cheap way to do this. You could try an x-ray machine transformer, but these don't have the power you are after, in most cases.

    -Clive Hansen
    Last edited: Jan 20, 2008
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook