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

Creating High Amps, Low Voltage

  1. Apr 25, 2004 #1
    I understand it's possible to create high voltages (low amps) with a Tesla Coil.

    How would I go about creating high amps yet on low voltages?

    IE: 1000a @ 3-6v
  2. jcsd
  3. Apr 25, 2004 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Given a Power supply capable of producing 1000A, all you would need is a low resistance capable of carrying 1000A.


    so 3V and R=.003 ohms should do the trick.

    The question of what material to use for the resistance and even better the power supply that will provide that much current remains unanswered.
  4. Apr 25, 2004 #3


    User Avatar
    Gold Member

    I think the original question was what kind of power supply will provide that type of voltage and current. Off the top of my head, I'd say a faraday disk. I believe I have the name correct. A brush on the outside of the disk, a brush on the shaft, a magnet placed next to the disk between the brushes. Often times a liquid metal of some kind is used for brushes.

    You may also consider getting a very large battery such as something that would have come out of a semi tractor. Of course the lowest voltage I know of is 6 volts, but it is 2 volts per cell if you want to disect one. If the battery is good for 1000 amps, then each cell is too because they are wired in series. Also, the phone company has used very large batteries in the past. I don't know if they still use them. They had a VERY large plate area and I believe were a lead acid battery so they would be 2 volts per cell. It goes without saying to be careful around lead acid batteries. Not only is there danger of severe burns in the event of a short circuit, there is danger of explosion. I have seen and been around lead acid batteries that explode. It gives you alot more respect for them after seeing one go up. Sometimes even after a battery explodes and the top is totally removed it will still turn the starter enough to start an engine. Just because the battery has exploded does NOT mean the danger is gone.
  5. Apr 26, 2004 #4
    Couldn't you collect bunch of capicators and then discharge then all at once? :P There is your high current!

    Anything wrong with using a capicator in this case?
  6. Apr 26, 2004 #5


    User Avatar
    Science Advisor

    You're question is about supplying 3000W to 6000W of power, a lot more than you can pull from a regular household outlet or even a couple regular car alternators at full output. So your level of difficulty is increased a little bit, and as you can see from Integral's post even .001 ohms resistance is a large voltage drop as a percentage of total voltage (and a lot of wasted power in terms of efficiency) so you're likely using 0000 gauge wire or something like it to minimize transmission loss.

    Batteries would be the easiest, definietly vent them (even the 'sealed' ones) to avoid gas buildup and be ready to have plenty of capacity as the lifetime of the batteries is substantially shortened if you discharge them too far. For a regular 12V battery the CCA (cold-cranking amps) is rated at 7V and near freezing, so by guesstimation the 6V battery should get you in the ballpark.

    There are some heavy-duty 6V batteries for marine use that have a rating of 180Ah to 200Ah which is big when you consider a regular car battery is only 50Ah or so! Five of those marine batteries in parallel would get you the 1000A with a nice long useful lifetime close to 20 hours, if that's important.

  7. Apr 26, 2004 #6


    User Avatar
    Science Advisor

    Hmm, lets see what we'd need for .1 second of discharge.

    V(t) = V0 * e^(-t/RC)

    C = - t / (R * ln (V(t) / V0))

    C = -.1 / (.003 * ln(3/6))

    C = 48 Farads

    Now a cap that large would need the ESR/ESL factored in as well, and hopefully the electrolyte wouldn't get cooked out from the heat of discharge.

  8. Apr 26, 2004 #7


    User Avatar

    Staff: Mentor

    Bottom line here: you'll need to be a little more specific about what you're trying to do.
  9. Apr 26, 2004 #8
    Transformer, of course. Primary coil is some 20-100 turns of heavy wire, heavy core, secondary coil is single or half turn of, umm, just huge brick of metal. Mains line in, huge amps out at low volts.
  10. Apr 26, 2004 #9
    A Faraday Disk looks like something I'd be interested in - if it actually works.

    Battries would be my second option.

    To me, capacitors are like little explosives. I don't like snap, crackle or pop. :)

    A transformer would've been my first guess, but I don't want to have to be connected to mains.

    What I'm wanting to do is create a huge electromagnetic field - like a degausser coil, but using pulsed DC. My thinking is the eM field comes from amps, not voltage. Is this correct?
  11. Apr 26, 2004 #10


    User Avatar
    Gold Member

    If you don't like snap crackle and pop, then I don't know if this is something you should pursue.
  12. Apr 26, 2004 #11


    User Avatar
    Science Advisor

    BTW I was mistaken above, your batteries would last about 20 minutes not hours. So 300lbs of batteries costing $1200 or more last 20 minutes.

    Mains power isn't big enough for your original spec unless you're going 240V for your mains.

    You're talking a big field like an MRI uses right? Some of those things had like 20KW amps in them made by Crown (the pro-audio guys) and that's going to need 480V 3-phase power.

    There's going to be big caps somewhere, likely inside the amplifier you find to drive your coil.

  13. Apr 27, 2004 #12
    To create a huge electromagnetic field you do not need huge amps, you need number of turns in the electromagnet coil. Wire resistence is then just a thing of efficiency, ie losses. Voltage is needed to just overcome the losses. If you get your wires to supercnduction, no voltage is needed.

    Tokamak magnetic coils come to mind.

    Re crackle and pops, eletric welding uses like 200 amps. If you want to go past 1000A, you don't mean to say that this is some easy stuff?
  14. May 10, 2004 #13
    So... if I have two coils of the exact same size, yet one uses 0AWG cable and the other uses 12AWG wire... the magnetic fields should be the same for both if the power supplied, as well as the number/size of turns, is the same?

    Somehow that doesn't seem right. I have the idea that one needs to squeeze more power through a wire in order to get a higher magnetic field. This is false?
  15. May 13, 2004 #14
    You need current to produce magnetic field. Smaller wire will have higher resistence, so to get same amount of current you'd need more voltage. When you get to same current through both, same magnetic field will be made.

    In regards to power, its a measure of work done over time. Magnetic field byitself is not any work done, only heat dissipation in the wire resistence is. Thus smaller wire will dissipate more heat - more losses.

    Power to the magnetic field will become an issue when the field interacts to make some real work.

    I guess you can think of magnetic field as of transmission line of power grid. You don't want to get much power AT the wires, you want to get as much as possible _through_ it with minimal losses. Ideal wire is that with zero resistence, needing zero volts to transfer infinite amps with no losses, an so is magnetic coil too.
  16. May 24, 2004 #15


    User Avatar
    Science Advisor

  17. May 24, 2004 #16


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Gee... There is no price listed on that page... Anybody care to guess what that beauty might run? $10k? These guys are accustomed to dealing with industry, not a home hobbyist, they expect to get paid. Maybe even $20k, more would not surprise me, less would.
  18. May 24, 2004 #17


    User Avatar
    Science Advisor

    Details my friend, small details... :biggrin:
  19. May 24, 2004 #18


    User Avatar
    Science Advisor

    Actually, come to think of it, I suppose that if you hook
    that thing with a very low resistance circuit it could just
    short circuit, so eventually you'll just get a part of those
    phousands of amps. But, maybe I'm wrong and it won't
    short circuit, don'no... :confused:
  20. May 24, 2004 #19
  21. May 27, 2004 #20
    I second this motion. Strong electromagnetic fields are created most easily by adding many turns of wire to your electromagnet just making sure you have enough voltage to get through the resistance.

    "The simplest electromagnet is a wire through which a current is flowing. If the wire is now wound into a coil or solenoid, the strength of the magnetic field is increased to a very large degree. This increased strength is due to the fact that the field around each turn of the coil adds its effect to the fields of all the other turns, just as would occur if a number of permanent magnets were tied together. The resultant magnetic field is the sum total of all the individual fields."

    -Basic Electrical and Electronic Principles

    Maurice Grayle Suffern

    McGraw-Hill 1949 3rd edition: 1962

    He goes on to cite the following four factors that contribute to the strength of any electromagnet:

    "1. The number of turns forming the solenoid.
    2.The strength of the current flowing through the solenoid.
    3.The material of which the core is made.
    4.The size of the core."

    Whatever kind of iron based core you use will have a somewhat different ability to be magnetized, depending on what elements have been added to the iron and in what proportions. In general, though, the larger the core the stronger the possible field.

    All forms, however have a saturation point beyond which it is no longer possible to increase the strength of the magnetic field by adding more turns.

    Putting mega-current through a coil of few turns is not a good solution because of the heating. The best solution is to put a reasonable current through many, many turns of wire with a good sized core.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook