|MadSci Network: Engineering|
If you are doing a project with any electrical equipment it pays to understand the concepts of VOLTAGE and CURRENT. A Van De Graaf generator supplies enormous VOLTAGES, but very low CURRENT, unless extra (dangerous) measures are taken. Lets say at the outset, that, for all practical purposes CURRENT is what kills. It takes voltage to drive current, so you can't have current without some voltage, but current, particularly if directed through the heart can kill. It takes as little as 0.001 amp (1mA) to kill a sick person, but often more than 100mA to kill a fit person. In fact what matters more is the ENERGY transferred, which is related by current and voltage as energy = voltage x current x time. This is why defibrillators, those miraculous devices beloved of Hollywood for resuscitating the "dead", or certainly the soon to be dead are calibrated in JOULES (units of energy), not voltage. Your mileage may vary. Don't try this at home boys and girls..... ANALOGY Your question seriously confuses voltage and current. A water tank analogy always helps here. Take a very large tank of water, so big that there is no appreciable change in its level as water flows out of it. Make a hole in it near the top. A trickle of water runs out. The PRESSURE of water behind the hole causes a CURRENT of water to emerge.If you gather the water in a bucket, you have stored CHARGE. The rate of flow of charge is the definition of current. 1 Coulomb of charge flowing in 1 second is called 1 Amp. Knock another hole in the tank, lower down, the water jets out further and more comes out. The energy in the emerging stream has increased. At the risk of pushing my analogy way too far, note that all real energy sources allow current out of the tank through a hole, the available power is a function of the size of the hole ! Your VDG generates lots of volts (pressure), but not much flow rate (current). Changing the output circuits may increase the capacitance, and an engineer should determine if the proposed change can create a hazard. Now what REALLY causes problems with electrical safety is the storage of electricity in Capacitors.A capacitor can deliver a virtually unlimited current. A capacitor is like a bucket of water that is emptied quickly.... Your 30 Amp figure for a human body discharge is actually pretty credible- and it can be fed from 20,000 Volts or more, but the capacitance of a human body is very small indeed, and not much energy is stored in it. When you discharge the stored charge (at high voltage) to the door handle, a PEAK current of 30 Amps or more can flow. The capacitance is so low that the energy transfer is only sufficient to make you yelp. Energy in a capacitor is related by E=1/2 * C*V^2 I do not know the size of the spheres on your VDG, but the size determines the capacitance of the spheres, and yours are unlikely to be more than 4 or five inches across. Not knowing that means I can't estimate the capacitance, I don't know the voltage, and I don't know what you are discharging from, so I can't estimate current ! Old VDG could have incredibly large spheres and have a very high energy storage capability. These things would blow you to a plasma ! Basically don't worry. Though the volts are scarily high, the current kills you, and by design there isn't enough energy to harm you. But it will make you jump if you aren't careful..... Steve
Try the links in the MadSci Library for more information on Engineering.