I'm not sure if I should be asking this this type of question here, but couldn't find another suitable newsgroup, so here goes, I'm building a power supply for a regen radio that consists of two wallwarts, in series delivering 23 volts 300 mA each, for a total of
46 volts, 300 mA. I'm not sure if this type of voltage and current is dangerous, what would happen if I accidentally touched both the B+ line and the B- line, or ground connection at the same time? Would I just receive a small electric shock? If it's too dangerous, I'll just stick to 5, 9 volt batteries in series. Thanks
In general that amount of voltage will not do anything. Even 120 is usually not lethal in most circumstances(I don't mean that you go around playing with it but I mean in most accidents when people get shocked).
At around 50V or more is when there is enough voltage to start to break through the skin. Your skin is essentially like a resistive coating. It has a high resistance but is thin. If the skin is wet or broken(With fluids) then its worse Dry skin has about 500kOhm resistance so its no big deal. (at
100V thats only 0.2mA which is not enough to kill)
Wet skin is like 1kOhm so its 500 times more likely to get shocked if your wet. This means its about 100mA(@100V) and enough to kill if it goes through your heart.
Note though that the current does not flow ont he surface of your skin but goes into your fluids where there are electrolytes and its much less resistive(essentially your veins are like copper wires and your skin like a resistor).
This is why the 9V shocks your tonge. Its probably sending an aweful lot of current(probably 50mA is my guess on average) but does nothing because its only on your tonge. (although I imagine a 9V can kill if placed "across the heart".
The real issue is not shock. Its getting shocked in such a way that current passes through your heart. (although serious burns can occur otherwise but its usually rare)
The trick in working with "high voltage" is never to use two hands. The reason why most people who die from electric shock is because they use two hands and current will flow from one hand, through the blood into the heart then out the other hand. Use one hand and probably at most you'll get shocked. You can also wear some gloves if your still afraid. (even with one hand its possible the current will go through your heart but much less likely. If the other parts of your body are not being grounded in any way then it's usually ok)
Main's is much worse because ground is earth ground. If you are working on a power supply then you usually use a transformer and the only way to get shocked is for your body to make a circuit with the ground on the secondary side. This is pretty much impossible(except on your hand) if you keep one hand away. (although there are allways accidents)
I think as long as you are careful then it will be ok. Its about 30kV/cm for voltage to be able to "get you" through air. This means at 100V its only like 33um. (about the size of a human hair)
The main thing is to just think about what your doing and don't be clumsy. If you pay attention to what your doing and know the dangers and what is dangerous in what your trying to measure then usually you'll be ok. Then, in the rare chance that you get shocked usually it's not fatal. Its basically like driving a car.
I knew about the one hand in pocket technique. The radio has exposed fahnestock clips for the power, so I'll have to be really careful, applying power only when my hands are clear, and keeping the cats out of the room when operating the set. Would the set have hum powered from these switch mode power supplys? I have a 2200 MFD 50 volt cap I can use for a filter cap if needed.
Shocks are a total of the voltage, the current, the state of your body and even how you touch the voltage.
It's "safe" to touch much higher voltage, if by safe you mean "not fatal". On the other hand, when it happened to me a few times decades ago, I realized I didn't want it to happen again, especially not after I hurt my arm (though not-seriously) when my hand jumped off the high voltage and banged against a hard surface.
For someone else, that voltage might have been fatal. Or, if it had gone from one hand to the other, rather than from the finger to the side of my hand that was about what happened.
The 9v batteries in series can be as dangerous as a 45volt power supply (or as "safe"), the voltage is the same. The current of the power supply is likely more, but then few think about the potential danger of running 12v through their body at really high current.
"Safety" is also relative given the care you take. If you never touch the voltage, you will always be safe no matter what the voltage or current. But if you're careless, the safety starts disappearing.
But that open style that was common in the early days is dangerous. One famous Australian ham died a long time ago when he was doing something and his headphones brushed against some high voltage, and he was known for his techical writing so he should have known better.
Exposed wiring makes things a lot more dangerous than the voltage or curent of the power supply. It's just too easy to accidentally brush against something.
It isn't a joke, I have seen stories about people's cats dying when they brush against high voltage, and the only reason that can happen is because the high voltage isn't properly kept inside a box.
Use two needles stuck into your veins. You will probably get enough current to cause serious shock or even death if placed properly.
For the OP's circuit, with either batteries or wall-warts (especially with a big capacitor), it might be good to rig up a simple current limiter, for about 5-10 mA, and enclose the whole thing in an insulated box.
An LTspice schematic follows. It limits short circuit current to about 5 mA, but provides 44.6 VDC into a 10 kOhm load or higher. However, it draws a constant 93 uA from the battery. You can fiddle with the values, and maybe use a darlington (but you need to add an extra diode). It is also possible to build this with a PMOS transistor with negligible current draw with no load, but a little more power in the sense resistor while operating.
There is a real difference between AC and DC wrt current across the heart. DC, even in very high voltages, has the effect of clenching the muscles. So, a DC shock may stop your heart, but only when you are holding it. If you can let go,, you are probably going to be OK.
On the other hand, AC has the effect of putting the heart into fibrillation. This is often lethal, and actually used to be treated by passing a DC current (by charging big caps up to 1000V!) across the heart, which stops it and resets it. They now use a sine waveform (which is AC, actually, but is about 100Hz) that uses less energy, and thus causes less damage.
It doesn't really matter. If you get shocked through the heart by DC there is much more likely to be serious injury to the muscles and blood vessles than with ac. Also, if the DC is high enough you can actually create an electrolytic effect in the blood stream.
Would you rather get ran over with a tank or hit by a plane? Either way your dead so it does't matter much. (also 50VDC is not 50VAC rms so you can't compare them directly)
I would aggree that AC probably has a higher chance causing fibrillation than DC because of the way the heart is designed. But I would imagine that chances are if you get shocked with DC power or equal AC power across the heart that both with have approximately the same outcome. (although I really have no idea exactly how they are related. AC may be worse at low voltages than DC and maybe DC is worse at high)
And a fully discharged AAA cell can kill you if fired from a gun. Or if you eat enough of them. :)
Not at all. It's a good idea, at least, to know how to rig up a current limiter, especially when it can be built for less than the cost of one of the batteries. It could prolong their life in the case of an accidental short circuit or overload, and it would be very much advisable for Lithium batteries which can explode if short-circuited.
Here's the MOSFET version, using only four cheap parts: