Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
ScottH, Sun Feb 19 2017, 02:42PMLets say you have a TENS unit that puts out 70v@6ma through the body (assume a 60hz pattern). The unit can only put out 6ma through the body, no more.
If they made a TENS device that puts out 7,000v@6ma through the body with the 60hz pattern, and the device was designed to only put out 6ma through the body, would it feel any different?
I know there is 100x the energy present (wattage) in the "7,000v unit", but the current flowing though the body is exactly the same. If there is a difference, what would it be (more burning, shocking, etc.) and why? I have always wondered.
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
hen918, Sun Feb 19 2017, 05:10PM
Ohms law is V = IR. This cannot be avoided. The voltage and current depend on the resistance. Which isn't actually constant with regards to the human body, but it cannot be changed. If a device put 70 V at 6 mA across / though the body, the resistance would be 12 kOhms. If the voltage was 7000 V the resistance would be 1.2 MOhms. This is higher than the human body, and therefor impossible.
hen918, Sun Feb 19 2017, 05:10PM
Ohms law is V = IR. This cannot be avoided. The voltage and current depend on the resistance. Which isn't actually constant with regards to the human body, but it cannot be changed. If a device put 70 V at 6 mA across / though the body, the resistance would be 12 kOhms. If the voltage was 7000 V the resistance would be 1.2 MOhms. This is higher than the human body, and therefor impossible.
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
Enceladus, Sun Feb 19 2017, 07:19PM
If you're only defining the current then you're talking about a current source, not a voltage source. The voltage developed by a current source connected across a resistor will depend only on the value of the resistor. Conversely, if you connect a fixed voltage source to a resistor, the current in the circuit depends only on the resistor. Current sources develop more power as resistance increases and voltage sources develop more power as resistance decreases. Ohm's law man. Learn it. Know it. Never forget it.
Enceladus, Sun Feb 19 2017, 07:19PM
If you're only defining the current then you're talking about a current source, not a voltage source. The voltage developed by a current source connected across a resistor will depend only on the value of the resistor. Conversely, if you connect a fixed voltage source to a resistor, the current in the circuit depends only on the resistor. Current sources develop more power as resistance increases and voltage sources develop more power as resistance decreases. Ohm's law man. Learn it. Know it. Never forget it.
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
Sulaiman, Sun Feb 19 2017, 08:36PM
current vs. voltage for human bodies is complex and non-linear.
If you hold two wires with 70V difference, what happens, and what you feel, will be different depending upon so many factors,
the most important thing to remember is that there is a recorded death by multimeter battery
so don't go poking probes in yourself, like I used to .........
Sulaiman, Sun Feb 19 2017, 08:36PM
current vs. voltage for human bodies is complex and non-linear.
If you hold two wires with 70V difference, what happens, and what you feel, will be different depending upon so many factors,
the most important thing to remember is that there is a recorded death by multimeter battery
so don't go poking probes in yourself, like I used to .........
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
ScottH, Mon Feb 20 2017, 03:02PM
I know and respect Ohms Law, but you all misunderstood my scenario.
Lets say the human body's resistance with the TENS pads and conductive gel is 1,000 ohms between the electrodes. 70v would allow a max of 70ma through the body, which is the rated voltage output of the unit. The device can only do around 6ma regardless (according to the label), so only 6ma is available to go through the person.
Now lets say they sold one that put out 7,000 volts. 7,000v is capable of pushing 7 full amps through the human body in this scenario (1,000 ohms). If the transformer of the unit was only capable of supplying 6ma of current, then only 6ma would be available to go through the person.
*One good example of what I am explaining is a stun gun. It may put out 50,000v, but with the overall power supplying it (battery), then there is only 5-30 ma of current max. Stun guns do not kill or do much damage, if any. That is not the same as touching a 50,000v power line (which would fry you). Both sources have 50,000v, and Ohms Law applies to both shocks, but one has limited current to "give" and the other is practically unlimited.
ScottH, Mon Feb 20 2017, 03:02PM
I know and respect Ohms Law, but you all misunderstood my scenario.
Lets say the human body's resistance with the TENS pads and conductive gel is 1,000 ohms between the electrodes. 70v would allow a max of 70ma through the body, which is the rated voltage output of the unit. The device can only do around 6ma regardless (according to the label), so only 6ma is available to go through the person.
Now lets say they sold one that put out 7,000 volts. 7,000v is capable of pushing 7 full amps through the human body in this scenario (1,000 ohms). If the transformer of the unit was only capable of supplying 6ma of current, then only 6ma would be available to go through the person.
*One good example of what I am explaining is a stun gun. It may put out 50,000v, but with the overall power supplying it (battery), then there is only 5-30 ma of current max. Stun guns do not kill or do much damage, if any. That is not the same as touching a 50,000v power line (which would fry you). Both sources have 50,000v, and Ohms Law applies to both shocks, but one has limited current to "give" and the other is practically unlimited.
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
DekuTree64, Mon Feb 20 2017, 04:58PM
If the supply can't provide the amps, the voltage drops accordingly. That stun gun is only 50kV until it makes contact, and then it drops very quickly. You still get the high voltage effects (long sparks, powerful static E field), but as soon as the charge starts moving, you have to re-evaluate the situation.
With the TENS machine, if it's pushing 6ma through 1000 ohms, then the voltage must have dropped to 6V. But if it's capable of a continuous 6mA at 70V (i.e. it can push 6mA through a resistance of 11.6kOhms), then the only reason the voltage would drop with the lower resistance is because of a current limiting device.
A 7kV TENS machine could potentially feel different because high voltage can pierce the skin, establishing a low resistance path into the low resistance blood/nerves. Then it would have to drop the voltage drastically to keep the current low. But the low current would probably allow the low resistance path to dissipate, so then it would have to adjust the voltage back up to 6V like the regular machine to maintain the specified 6mA current. So my best guess is that you'd get a small sting on contact, after which it would feel the same as usual... assuming it charges to the full 7kV when no current is flowing. In reality the control circuitry would probably keep the voltage low until a small current is detected, and then adjust up until the target is reached. So the 7kV supply on 1kOhm skin would be no different at all.
DekuTree64, Mon Feb 20 2017, 04:58PM
If the supply can't provide the amps, the voltage drops accordingly. That stun gun is only 50kV until it makes contact, and then it drops very quickly. You still get the high voltage effects (long sparks, powerful static E field), but as soon as the charge starts moving, you have to re-evaluate the situation.
With the TENS machine, if it's pushing 6ma through 1000 ohms, then the voltage must have dropped to 6V. But if it's capable of a continuous 6mA at 70V (i.e. it can push 6mA through a resistance of 11.6kOhms), then the only reason the voltage would drop with the lower resistance is because of a current limiting device.
A 7kV TENS machine could potentially feel different because high voltage can pierce the skin, establishing a low resistance path into the low resistance blood/nerves. Then it would have to drop the voltage drastically to keep the current low. But the low current would probably allow the low resistance path to dissipate, so then it would have to adjust the voltage back up to 6V like the regular machine to maintain the specified 6mA current. So my best guess is that you'd get a small sting on contact, after which it would feel the same as usual... assuming it charges to the full 7kV when no current is flowing. In reality the control circuitry would probably keep the voltage low until a small current is detected, and then adjust up until the target is reached. So the 7kV supply on 1kOhm skin would be no different at all.
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
Physikfan, Tue Feb 21 2017, 01:35PM
If I would be not very polite I would say
Your question is inconsistent with
Ohm's law.
If you want to get the same current
Through your body by applying different voltages
The only possibility is you have to
Change your body's resistance.
Physikfan, Tue Feb 21 2017, 01:35PM
If I would be not very polite I would say
Your question is inconsistent with
Ohm's law.
If you want to get the same current
Through your body by applying different voltages
The only possibility is you have to
Change your body's resistance.
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
ScottH, Tue Feb 21 2017, 02:34PM
So no matter the voltage, voltage drop is directly proportional to the current going through the resistance?
If I got zapped by an ignition coil with 40,000v and it only put out 40ma, the voltage going through my body drops to 40v due to resistance?
ScottH, Tue Feb 21 2017, 02:34PM
So no matter the voltage, voltage drop is directly proportional to the current going through the resistance?
If I got zapped by an ignition coil with 40,000v and it only put out 40ma, the voltage going through my body drops to 40v due to resistance?
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
hen918, Tue Feb 21 2017, 05:15PM
If your body has a resistance of 1 kOhm, yes, that's exactly right.
hen918, Tue Feb 21 2017, 05:15PM
ScottH wrote ...
So no matter the voltage, voltage drop is directly proportional to the current going through the resistance?
If I got zapped by an ignition coil with 40,000v and it only put out 40ma, the voltage going through my body drops to 40v due to resistance?
So no matter the voltage, voltage drop is directly proportional to the current going through the resistance?
If I got zapped by an ignition coil with 40,000v and it only put out 40ma, the voltage going through my body drops to 40v due to resistance?
If your body has a resistance of 1 kOhm, yes, that's exactly right.
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
Physikfan, Tue Feb 21 2017, 08:03PM
Hi ScottH
According to your first question I think
you got Ohm's Law.
Physikfan, Tue Feb 21 2017, 08:03PM
Hi ScottH
According to your first question I think
you got Ohm's Law.
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
ScottH, Tue Feb 21 2017, 10:26PM
Wow, I learned something new today! Now that I understand Ohm's Law, I have a question.
If the voltage drops so much, why would the spark keep jumping to your skin? Doesn't it take a couple thousand volts to make a spark jump?
One example would be shocking a piece of meat with an ignition coil setup. It will still make a 1cm arc to the meat with ma current flow, and the spark dims. Doesn't it take 10,000v to make a spark jump 1cm through air?
Is the voltage drop to 400v inside the meat (100 Ohms) only when the electricity is flowing inside the meat? The arcs can jump 5mm on each contact point.
Can somebody elaborate? Thanks.
ScottH, Tue Feb 21 2017, 10:26PM
Wow, I learned something new today! Now that I understand Ohm's Law, I have a question.
If the voltage drops so much, why would the spark keep jumping to your skin? Doesn't it take a couple thousand volts to make a spark jump?
One example would be shocking a piece of meat with an ignition coil setup. It will still make a 1cm arc to the meat with ma current flow, and the spark dims. Doesn't it take 10,000v to make a spark jump 1cm through air?
Is the voltage drop to 400v inside the meat (100 Ohms) only when the electricity is flowing inside the meat? The arcs can jump 5mm on each contact point.
Can somebody elaborate? Thanks.
Re: Will 7,000 Volts Feel Different than 70 Volts, if they Both Put Out the Same Current?
Physikfan, Wed Feb 22 2017, 06:43AM
There is another law, Kirchhoff`s law:
The sum of all the voltages around a loop is equal to zero.
"If the voltage drops so much, why would the spark keep jumping to your skin? Doesn't it take a couple thousand volts to make a spark jump? "
In your special case with the high voltage:
If there is no current, you get the full voltage at the future spark gap, because the resistance of a not operating spark gap is infinite, and all other resistances of this loop could be neglected, practically zero.
"Doesn't it take 10,000v to make a spark jump 1cm through air?"
Yes, but if the spark gap is operating the according resistance is quite low, could be in the order of around 100 Ohm.
"Is the voltage drop to 400v inside the meat (100 Ohms) only when the electricity is flowing inside the meat? The arcs can jump 5mm on each contact point. "
Yes.
Please see also here:
Physikfan, Wed Feb 22 2017, 06:43AM
There is another law, Kirchhoff`s law:
The sum of all the voltages around a loop is equal to zero.
"If the voltage drops so much, why would the spark keep jumping to your skin? Doesn't it take a couple thousand volts to make a spark jump? "
In your special case with the high voltage:
If there is no current, you get the full voltage at the future spark gap, because the resistance of a not operating spark gap is infinite, and all other resistances of this loop could be neglected, practically zero.
"Doesn't it take 10,000v to make a spark jump 1cm through air?"
Yes, but if the spark gap is operating the according resistance is quite low, could be in the order of around 100 Ohm.
"Is the voltage drop to 400v inside the meat (100 Ohms) only when the electricity is flowing inside the meat? The arcs can jump 5mm on each contact point. "
Yes.
Please see also here:
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