12v DC PWM with a few extras...

Discussion in 'General Electronics Chat' started by JDB57, Feb 24, 2008.

  1. JDB57

    Thread Starter New Member

    Feb 21, 2008
    2
    0
    Hi all. I am experimenting with HHO cells and I have been looking for a pulse width modulator for about a week now. I consider myself to be pretty internet savvy and thus I figure that I have searched high and low and still have not found exactly what I am looking for. I have seen the various sites that sell PWMs for fairly reasonable, but I am wanting a little more flexibility.

    THINGS I WANT:
    1.) Runs on 12v battery
    2.) Can reach the Mhz range
    3.) Has gating capabilities
    4.) Duty adjustment

    I am fairly new in my learning of electronics, but I was wondering if it was possible to somehow multiply the current post-PWM and still keep the assigned frequency. For example a circuit that goes: 12v, 5A, 1Mhz --> 6v, 10A, 1Mhz --> 3v, 20A, 1Mhz --> 1.5v, 40A, 1Mhz.....etc, until it reaches, say 1000A.

    From what I understand there are three techniques to extracting HHO gas:
    1.) Brute force 12v, 20-40 amps
    2.) standard 12v, low range amperage with pulses
    3.) 30kv, low amperage with pulses

    So, basically I want to experiment with lower voltages and higher amperages being pulsed. Now please tell me this is all possible? I have a feeling it is not, otherwise it would be readily available like the standard PWM designs.

    Thanks in advance!
     
  2. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    PWM circuits are not able to produce more current than what is normally possible given a fixed load and voltage. PWM control merely divides up the amount of voltage that can be applied to a load. Since it is fast, it can appear like a DC current across the load, rather than moving excessively.

    So, for example, if you have a 12V supply and a 1 ohm load, it doesn't matter at what frequency or duty cycle, you can only get a maximum of 12A through the load. These is neglecting I*Rdson losses though. With an h-bridge, you can get a maximum of +/-1A total flow with the same supply and resistance given, this is due to floating the load and the effect of bridging.

    I'm not sure what an HHO is, can someone clarify?

    You need to consider other parameters for your PWM, which you missed. First of all, is current capability. Second, is RDSon of the devices used, which determines power loss, that you need for an efficiency criteria(if you have one anyways) and thermal considerations. Finally, you're missing resolution of the PWM.

    You should specify your intentions with what you are trying to make, then we can offer some more insight.

    Steve
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,690
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  4. JDB57

    Thread Starter New Member

    Feb 21, 2008
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    0
    Thanks for the replies. I think I am just going to go with one of the PWMs that are pre-built, but I would like to build, as a separate experiment, a circuit that would divide the voltage and increase the current. Is this possible?
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Voltage and Current are correlated by Ohm's Law, I=V/R, so you can see that if you decrease voltage, you must decrease current. The only way to raise current with a lower voltage is to decrease resistance.


    Steve
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    You can decrease resistance, (thereby increasing current for a given fixed voltage) by moving your electrodes closer together. Exercise extreme caution, as hydrogen and oxygen combine explosively in the presence of an arc.

    Greater electrode surface area should also decrease resistance.
     
  7. watson.fawkes

    New Member

    Feb 25, 2008
    1
    0
    HHO is the reference to the evolute of water electrolysis as atomic gases, not molecular. The stored energy in such a mixture is higher, since the molecular combination reaction 2 H --> H_2 is exothermic.
     
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