The only purpose of a "black Max" type device is to discourage a carjacker. And as long as the discomfort is enough to stop them withing a very few seconds that is the only requirement. 40 amps from an automotive battery for even a whole minute would not be a big deal, which is why the power is not higher.
Besides, throwing a solid arc to a bad-guy's hand is a great psychological deterrent, don't you think?
Critic, with a model number like that I am certain that the intention is to mislead the potential buyer, which is something frequently done these days. Intentionally giving a false impression while technically not telling a lie. It happens all the time.
Great explanation, etmax. I didn't know that. Thanks much for the information. It could come in handy as we do future articles about defibrillators (which we have done on several occasions in the past).
Isn't it possible the stun gun is generating very high voltages (through capacitive discharge) but the distance seperating the elctrodes is simply governed by practical limitations (size of device, handling, ...etc) as opposed to the max voltage generated/dielectric breakdown of air (20-30K per inch)? In other words, I could generate 1MV (just an example, not feasible in such a small pachage without serious insulation), but choose to seperate the electrodes 1 inch only.
Hi Will, your calculations are sound but typically a 50,000V generator in a Blackmax type device while being able to deliver 10mA will only be able to supply 5W which means that the voltage will collapse to around 500V.
Of course 500V is plenty to push that 10mA through your skin and 10mA will feel decidecly uncomfortable
The 50kV is so that it will strilke an arc that will penetrate most clothing and while the voltage drop across the clothing may be as high as an additional 500V that still means 5mA which is a deterrent.
Re why only 5W?
Well from a car battery 500W means >40A@12V to produce it and also higher power cause death and liability :-)
On the side, if you removed the skin from a person's right and left hands (skin resistance is high) and attached their hands directly to the terminals of a 12V battery. you would most likely get enough DC current through the heart to defibrillate it. :-) it's all ohms laww
Interestingly, 120VAC is actually more dangerous generally than 240VAC because for vetricular fibrillation to set in the current has to be > than 60mA but less than 200mA. I've often received electric shocks from 240V and usually get local burns because the current is so high. This is a saving grace because it clamps the heart rather than rattling its rhythm.
Hi Charles, remember that the kiskstarter you describe uses 2 paddles that are placed on either side of the heart and use DC which clamps all muscles allowing a normal restart. A stun gun or taser places 2 electrodes 1-2 inches apart such that the current flows between them and the tissue engaged. Little or no current passes through the heart and it is pulsed DC (less than 10Hz) The current needed to cause vetricular fibrilation is > 60mA but < 200mA and the frequency needs to be between 20Hz and 150Hz. AND it has to pass through the heart, not 2 inches of skin. If you have a pacemaker or defibrilator installed the metrics change dramatically, and your emotional response to shock/stress can in sensitive individuals cause issues that may lead to death but that is reasonably rare. I would just hope that police know how to restart a heart. On the subject of high voltage and higher currents the issue is burning of subcutaneous tissue which can cause deadly levels of toxins in the blood and require amputation or other surgery, but neither stun guns or tasers get anywhere near that as you well know
Fibrillation usually sets in when the current is above 60mA but below 200mA and it has to cross the chest to trigger heart arythmia. Also the frequency would need to be 20-150Hz. A Taser places the electrodes a couple of inches apart (a stun gun too) as well as using pulsed DC < 5-10Hz this both limits the current through the heart and is to low in frequency to trigger arythmia
The problem with guns is the potential for fatal collateral damage. There's very few use cases where the police can use a gun safely. If they hit the wrong guy with a taser at least he will usually live to tell the tale (or sue if he meets an ambulance chaser). A stun gun probably has no collateral damage unless the cop is fool.
California State University, Chico was the first school in California to offer an ABET-accredited degree program in mechatronic engineering. Now its California Mechatronics Center works with industry on machinery, robotics, and surveillance vehicles.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.