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

Finding a Transformer for my application.

  1. Sep 21, 2008 #1
    I am electro-statically trapping particles for chemical and physical studies. I do not want to discuss the details of my research.

    AC Calibrators are very expensive and I don't need the precision. I did find a power amplifier that could step up my sine wave generator to the values I want, but that is some pretty good pocket change. My advisor says get a transformer. That is what he used in his post-doc days.

    However, it has been quite a challenge find a transformer than could take the max 7 V rms of the sine generator up to 1000 V rms. Finally after a few weeks of searching, I have found some models from Information Unlimited that has the step up I need, but I am afraid that the current is too low to drive itself through the transformer since that's a lot conductor (the one I was looking at weighs around 24 lbs). Even if it worked, my advisor told me it's a waste of money to buy all that. He said the transformer for our application should weight around pound or two. We are just interested in the potential.

    I have some quotes on custom transformers I am waiting and few of them are hesitant to make a really low power transformers in fear it will burn out. If had a short in my system , then burning out the transformer would be the least of my worries.

    Does anyone know if anyone makes step up transformers that can pretty much just steps up the voltage ? Something that is just used to generate the electric field.
    Last edited: Sep 21, 2008
  2. jcsd
  3. Sep 24, 2008 #2
    What current do you need at 1000 Volts? DC?

    An old CRT TV set will contain a line-output transformer which is capable of producing a small current when fed from a hefty valve or transistor driver ..few mA at 24 kV. So underun might give you 1000 Volts.

    Any system which can produce more than a few mA at 1000 volts is rather dangerous.

    An old microwave oven will contain a set-up transformer and rectifier but NEVER run it direct from the mains.. You might need an intermediate transformer to boost the voltage
    from your sine wave generator.

  4. Sep 24, 2008 #3
    I do realize that.... but I should be generating in the range of microamp. If I am generating power, it would there's a chance it will arc inside my chamber. You cannot trap particles that way.

    To Physicists it is called a Quadrapole trap to others it is a Electrodynamic Balance. It's a derivative of the device used in Millikan 's Oil Drop experiments. After Millikan's device, people added servomechanisms to give stability to aerosol particles. You cannot use just two plan DC plates. However, someone realized it is a lot easier to just put in a ring electrode between the two DC plates. With this device you can study micron size particles and single particle physics and chemistry.
  5. Sep 27, 2008 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Just a thought, would it make any sense to use 2 transformers, and do the step-up in 2 stages? The transformers would only need to have a 12x turns ratio, instead of the 140-150 required out of a single one.
  6. Sep 28, 2008 #5
    I have thought of that at times... put it in series and stuff, but now I am running into another issue.

    So, power is conserved therefore the current is steped down as the voltage is steped up. If my load has a current in the microamps to milliamps, then my sine wave generator will need to put out an Amp or so. It has a max current of the generator [tex]75 mA_{rms}[/tex].
  7. Sep 28, 2008 #6
    The final transformer has to be capable of handling 1000 volts..

    Transformer turns ratios only apply when a transformer is not loaded.
  8. Sep 28, 2008 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    You'll get at most 0.5 mA output after the transformer. Or a little less, with transformer losses. How much do you need? If your advisor has done this before, he might have some idea.

    If this generator is not enough mA, there's your argument for having your advisor pay for that expensive amplifier you mentioned earlier.

    Absolutely, yes.

    Valid point. It's best to use a transformer's input & output specs for v & i, rather than turns ratio (which may not even be given in the specs).
  9. Sep 28, 2008 #8
    I don't have a good way to figure out this load or measure the current. I been working on another student to caclulate the eletric field, but I have a feeling caculating the capcitacne from that will be challenging. It should be a few hundered microamps to a milliamp at most. It is not going to be prefectly zero.

    Current should be also low as possible. My experiments wouldn't work really well. I also probably would ruin a several thousand dollars of equipment and myself, since some parts, like my interrupt switch, are not rated for 1000 Vrms AC more like 700 or 800 Vrms. Yet, my current is really low, so they work "safely".

    I am really thinking of going with a transfomer in a series. I cannot find one single transformer to do what I want. Plus, most transformers I have found setup 115/220 V to whatever. It is alot easier to find a transformer to go from 115 to 1000 V. If I want to step up 7 to 1000 V that would be like 115 to 15000+ V.
    Last edited: Sep 28, 2008
  10. Sep 28, 2008 #9


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Right, and you don't need to pay for that 15,000 V rating.

    You haven't mentioned what frequency you are using. Transformers don't work equally well at all frequencies.
  11. Sep 28, 2008 #10
    I think a transformer from a microwave oven would do . I think they produce around 2Kv (somewhat higher with light loading) with 230 in Europe or 115 in the USA. Even buying a new oven might be cheaper than sourcing a transformer. They sell for £25 in supermarkets in the UK. Also you get a rectifier and some smoothing (might be wired for a negative HT is a microwave.

    Feed it with mains via two similar transformers.. Say 115 to 12 and then 12 to 115. Put a series variable resistor and a fixed one (to limit the max volatge)
    at the 12 volt stage. The resistors drops the voltage and provide some current limit.

    NEEDS to be constructed in a case for safety.
    REMEMBER to discharge any high voltage capacitors before working on the device.

    ANY DOUBTS - DON'T DO IT.. Stick to a low power source.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook