transforming alkaline batteries

Discussion in 'General Electronics Chat' started by semegraph, Apr 7, 2007.

  1. semegraph

    Thread Starter Member

    Apr 7, 2007
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    according to duracell, a fresh 1.5 volt battery, shorted with a wire with minimum resistance, draws 28 amps of current at 1.5 volts. If I understand wattage correctly (current x voltage), that means that for at least a short time 2 "D" batteries can output 84 watts of electricity (albeit in the form of 3 volts dc and for only a short time).

    Is it therefore possible to transform this output from 2 "D" batteries to output 1.5 milliamps (.0015 amps) at 28000 volts DC with a step-up? I would imagine the transformer would add some resistance, lowering the input amperage, but I don't know how much resistance. Would such a transformer need to be very large and heavy? If you drew enough current from this transformer, would that prevent it from arcing heavily?
     
  2. recca02

    Senior Member

    Apr 2, 2007
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    well. i dont know whats the latest developments in the field, but according to the principle isnt it the case that only ac signals can be transformed as they produce change in flux.
    mr thomas edison wud really have been pleased to know otherwise.
     
  3. semegraph

    Thread Starter Member

    Apr 7, 2007
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    but you could still rectify the AC output, right? Is it possible at all to convert something as low voltage as "D" batteries into voltages in the range of 30kv with a very very low current?

    I've seen lots of HV power supplies that plug into the wall, but is it possible to generate this kind of voltage from alkaline batteries? Would the transformer needed be huge?
     
  4. recca02

    Senior Member

    Apr 2, 2007
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    can u please tell me how do you plan on converting dc into ac (oscillator or invertor circuit?) , for transformation ac is required at primary and secondary ac can then be rectified.
    anyways if u achieve that transformation ratio i:e turn ratio of 1:20000 wud be required so i guess this means a rather bulky transformer
     
  5. goodbyegti

    Well-Known Member

    Apr 28, 2004
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    You could use a switch mode PSU, they use DC input and the transformer required is much smaller for the same power output than regular power supplies. You could find the device you're looking to create in a camera with a flash, or a LCD inverter.
     
  6. semegraph

    Thread Starter Member

    Apr 7, 2007
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    recca, i'm not sure how the conversion would be done, at this point it's just a hypothetical situation I am considering.

    goodbyegti, how can a switch mode PSU convert low voltage to high voltage more efficiently (smaller) than a step-up type transformer? If this is what flash cameras use, does that mean that the high voltage can only be sustained for a split second, or can the voltage be sustained for a few minutes?
     
  7. semegraph

    Thread Starter Member

    Apr 7, 2007
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    ok, i've been reading this,
    http://en.wikipedia.org/wiki/Switched-mode_power_supply

    there seem to be a number of different types, could you point out the type you are talking about? Also, this article doesn't explain very well what the transformer does in a switched mode PSU versus what the transistors do.

    Based on the comparisons and applications, it does seem like this is a step in the right direction
     
  8. semegraph

    Thread Starter Member

    Apr 7, 2007
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  9. semegraph

    Thread Starter Member

    Apr 7, 2007
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  10. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
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    Look at schematics for 'stun guns' or 'stun batons' they can crank a 9v up to 30kv
    They do this in most by converting the DC to high freq AC and then feed that to a transformer which goes through voltage doubler, tripler or more stages which yeild the higher voltages.

    The first one has a five stage circuit with each stage acting as a doubler so a 10X multiplier. The output of the transformer would be 3k. This allows a MUCH cheaper transformer to be used.
    http://www.personalarms.com/schematics.htm
     
  11. semegraph

    Thread Starter Member

    Apr 7, 2007
    12
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    wow, I think that stun gun schematic would be perfect, if it can be sustained. I don't see anything here that tells me it can't be.

    Since it's starting to seem like this isn't a completely ridiculous idea after all, I might as well tell you guys what application I am considering.

    http://jlnlabs.imars.com/lifters/arl_fac/0211001.pdf

    I've seen a lot of stuff on the net about these lifters, and it seems to me that the main problem with them is that they depend on a big hulking high voltage generator to supply the power to them.

    According to what I've seen around here, it takes about 30kv at only a few milliiamps to get one of these things in the air, so it does seem like it would be fun to experiment with using circuitry like this to convert power from a battery to high voltage to drive them.
     
  12. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
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    You need quite a substantial power at the input to be able to run these lifters.
    30kv times a few milliamps (let´s say 5mA) is 30,000*0.005=30*5=150W.
    You can´t squeeze that much out of four alcalines or anything simillar.

    Moreover you need to count with efficiency of the conversion, which can be quite bad for a home-made HV converter, so let´s say optimistic 50%. That brings us to 150/0.5=300W on the input side of the converter.
    This also means that you will get 150W in electricity to power the lifter, and another 150W in heat coming out of your converter.


    Why do you think that these things are allways powered from "big hulking high voltage generator"? Because you need something big and heavy to power it, and it is still isn´t posible to have it inside the lifter. The lifters weigh cca 5g, don´t they? Only the four AA baterries you talked about in the beginning will weigh many times more than the lifter, which is happy that it can hower in the air and lift the wires that provide electricity.
     
  13. semegraph

    Thread Starter Member

    Apr 7, 2007
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    there have been a number of lifters that can carry a payload. here is just one example, which carries 60g payload not counting the weight of the lifter, but there are many more.

    http://jlnlabs.imars.com/lifters/maximus2/index.htm

    It may be that the stun gun schematic posted to me earlier is way off, but it claims to output 30kv at 8 amps. The above lifter requires 18kV at 16.5 mA
     
  14. semegraph

    Thread Starter Member

    Apr 7, 2007
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    i don't really see how the stun gun could output 8 amps at 30kv from a 9 volt. perhaps they meant milliamps, but even then it would be enough to power the lifter above. Just to make sure it's clear, I am not an electronics student, just a beginner. Some of this terminology is not clear to me, so perhaps I am missing something obvious. Please fill me in if I am misunderstanding something.
     
  15. mrmeval

    Distinguished Member

    Jun 30, 2006
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  16. semegraph

    Thread Starter Member

    Apr 7, 2007
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    i see. Thanks for clearing that up. What I have read about these lifters is that the direction of force is not dependant on polarity, it always moves toward the smaller electrode, regardless. So, I am led to believe that an alternating current would still provide continuous thrust, although I have not yet seen anything about the effect pulsed current has on them.

    Would it be possible to spread this pulsed 8 amp current (at 30kv) to be a smoother output at a much lower amperage (less than 10 mA)? Again, although I haven't yet looked for lifter experiments done with AC, it is likely that AC would work as well as DC, in the event that it would be easiest to smooth out the voltage into an AC curve.

    Thank you all for taking the time to reply to my questions!
     
  17. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
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    the 8amp current stated in that schematic is probably a peak current into a short circuit. 8*30kV is 0.24MW, and nothing in your home can supply that much power..

    The output voltage after the multiplier wil probably be quite smooth, with not too big load.
     
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