[Poll]Death by USB?

[thescreensavers]

So, can you die if you get electrocuted from a USB port?

Off Wiki http://en.wikipedia.org/wiki/USB#Power

Power

The USB specification provides a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines.[16] There are two types of devices: low-power and high-power. Low-power devices draw 1 unit load, which is defined to be 100 mA. High-power devices draw 5 unit loads or 500 mA. All devices default as low-power but the devices' software may request high-power as long as the power is available on the providing bus.[17]

A bus-powered hub is initialized at 1 unit load and transitions to 5 unit loads after hub configuration is obtained. Any device connected to the hub will draw 1 unit load regardless of the current draw of devices connected to other ports of the hub (i.e 1 device connected on a 4 port hub will only draw 1 unit load despite the fact that 5 unit loads are being supplied to the hub).[18]

A self-powered hub will supply 5 unit loads to any device connected to it. A battery powered hub may supply 1 or 5 unit loads. In addition, the VBUS will supply 1 unit load upstream for communication if parts of the Hub are powered down. [19] USB On-The-Go and Battery Charging Specification both add new powering modes to the USB specification. The latter specification allows USB devices to draw up to 1.5 A (low and full speed or 900mA in Hi-Speed mode) from hubs and hosts or up to 1.8A for dedicated chargers that follow the Battery Charging Specification. The dedicated charger shorts the D+ and D- pins together and will not send or receive any information on those lines, allowing for the creation of very simple, high current chargers to be manufactured. The increased current (faster charging) will occur once the host/hub and devices both support the new charging specification.

As of June 14, 2007, all new mobile phones applying for a license in China are required to use the USB port as a power port.[20][21]

In September, 2007 the Open Mobile Terminal Platform?a forum dominated by mobile network operators but including manufacturers such as Nokia, Samsung, Motorola, Sony Ericsson and LG?announced that its members had agreed on micro-USB as the future common connector for mobile devices.[22][23]

[edit] Non-standard devices
A USB vacuum cleaner

A number of USB devices require more power than is permitted by the specifications for a single port. This is a common requirement of external hard and optical disc drives and other devices with motors or lamps. Such devices can be used with an external power supply of adequate rating, which is allowed by the standard, or by means of a dual input USB cable, one input of which is used for power and data transfer, the other solely for power, which makes the device a non-standard USB device. Some external hubs may, in practice, supply more power to USB devices than required by the specification but a standard compliant device must not depend on this.

Some non-standard USB devices use the 5 V power supply without participating in a proper USB network. These are usually referred to as USB decorations. The typical example is a USB-powered reading light; fans, mug heaters (though some may include USB hubs[24]), battery chargers (particularly for mobile telephones), miniature vacuum cleaners, a miniature Lava Lamp, and even toy missile launchers are available. In most cases, these items contain no digitally based circuitry, and thus are not proper USB devices at all. This can theoretically cause problems with some computers ? the USB specification requires that devices connect in a low-power mode (100 mA maximum) and state how much current they need, before switching, with the host's permission, into high-power mode.

In addition to limiting the total average power used by the device, the USB specification limits the inrush current (to charge decoupling and bulk capacitors) when the device is first connected; otherwise, connecting a device could cause glitches in the host's internal power. Also, USB devices are required to automatically enter ultra low-power suspend mode when the USB host is suspended; many USB hosts do not cut off the power supply to USB devices when they are suspended since resuming from the suspended state would become a lot more complicated if they did.

There are also devices at the host end that do not support negotiation, such as battery packs that can power USB powered devices; some provide power, while others pass through the data lines to a host PC. USB Power adapters convert utility power and/or power from a car's electrical system to run attached devices. Some of these devices can supply up to 1 A of current. Without negotiation, the powered USB device is unable to inquire if it is allowed to draw 100 mA, 500 mA, or 1 A.

The Apple SuperDrive uses a non-standard IDE-USB controller to negotiate with the MacBook Air to draw 1.5 A from the USB port.[25] Even with hub supporting the necessary current, SuperDrive may not work with generic hubs.[26] A workaround is to use a replacement IDE to USB bridge.[27]

[edit] PoweredUSB

Main article: PoweredUSB

PoweredUSB uses standard USB signaling with the addition of extra power lines. It uses 4 additional pins to supply up to 6A at either 5V, 12V, or 24V (depending on keying) to peripheral devices. The wires and contacts on the USB portion have been upgraded to support higher current on the 5V line, as well. This is commonly used in retail systems and provides enough power to operate stationary barcode scanners, printers, pin pads, signature capture devices, etc. This proprietary implementation was developed by IBM, NCR, and FCI/Berg. It is essentially two connectors stacked such that the bottom connector accepts a standard USB plug and the top connector takes a power connector.

Posted from http://hypertextbook.com/facts/2000/JackHsu.shtml

Cutnell, John D., Johnson, Kenneth W. Physics. 4th ed. New York, NY: Wiley, 1998.

"Currents of approximately 0.2 A are potentially fatal, because they can make the heart fibrillate, or beat in an uncontrolled manner."

0.2 A

Carr, Joseph J. Safety for electronic hobbyists. Popular Electronics. October 1997. as found in Britannica.com.

"In general, for limb-contact electrical shocks, accepted rules of thumb are: 1-5 mA is the level of perception; 10 mA is the level where pain is sensed; at 100 mA severe muscular contraction occurs, and at 100-300 mA electrocution occurs."

0.1?0.3 A

"Electrical Injuries." The Merck Manual of Medical Information: Home Edition. Pennsylvania: Merck, 1997.

"At currents as low as 60 to 100 milliamperes, low-voltage (110-220 volts), 60-hertz alternating current traveling through the chest for a split second can cause life-threatening irregular heart rhythms. About 300-500 milliamperes of direct current is needed to have the same effect."

0.06?0.1 A
(AC)

0.3?0.5 A
(DC)

Zitzewitz, Paul W., Neff, Robert F. Merrill Physics, Principles and Problems. New York: Glencoe McGraw-Hill, 1995.

"The damage caused by electric shock depends on the current flowing through the body -- 1 mA can be felt; 5 mA is painful. Above 15 mA, a person loses muscle control, and 70 mA can be fatal."

0.07 A

Watson, George. SCEN 103 Class 12. University of Delaware. March 8, 1999.

"0.10 death due to fibrillation > 0.20 no fibrillation, but severe burning, no breathing"

0.1?0.2 A

Miller, Rex. Industrial Electricity Handbook. Peoria, IL: Chas. A. Bennet, 1993.

"Currents between 100 and 200 mA are lethal."

0.1?0.2 A

 

[mageslayer]

No.

 

[JohnCU]

why the poll? of course you can die from USB, if you could lower your skin resistance to that point (bath in salt water, cut in skin across the chest?)

 

[IronWing]

You'd have to try pretty hard to complete the circuit in such a manner as to get the 5V drop to pass through your heart. Like strip the USB cable, take the hot lead and stab it into your neck and stab the ground lead into your pelvis to get the current to pass through your heart. Even with that, I still think it unlikely. Post photos.

 

[Rubycon]

Not in normal circumstances. If you add lots of attached equipment and really try you can. Of course that's true with just about anything else! :laugh:

 

[PottedMeat]

Originally posted by: ironwing
You'd have to try pretty hard to complete the circuit in such a manner as to get the 5V drop to pass through your heart. Like strip the USB cable, take the hot lead and stab it into your neck and stab the ground lead into your pelvis to get the current to pass through your heart. Even with that, I still think it unlikely. Post photos.

OP should demonstrate. Post video to YouTube.

 

[destrekor]

Only one of those quotes even brought into question voltage, and that only mentioned voltage like 110v.
Can 500mA at 5v kill a man? I don't think so.
5v at 1.5A? That might be getting into some serious hurt, but I don't think it's going to cause any real harm, but I am not sure at that kind of voltage.

PoweredUSB? That's something I don't think that is found all that often, as it uses extra pins for power delivery? Does this even exist for consumer use, and not just business? Regardless, that's approaching the area where it might very well provide lethal, but again, the voltage I'm not sure. DC requires more amperage, and that is what all computer peripherals operate on (devices that connect only to the PC for power). Voltage is still the question.

Can the max, say 24v at 6A kill a man? That's about the only one I'd say has any potential.

Ever connected a few 1.5v batteries in series and touched the bare wire? It provides a good shock and burning sensation, but other than that no harm. I've done that with a 1.5v batteries, so 4.5v's, at... what's a typical AA battery's amperage? And does amperage increase when in a series? Regardless, at a minimum it's a few hundred mA, but I expect it's more considering rechargeable AAs carry sometimes upwards of 2400mAh (and I'm not extremely knowledgeable in electricity, so if you connected a few 2400mAh batteries in series, what you get on the wire? Any amperage to even speak of? Is the amperage only going to be measurable if it's actually be drawn by electrical equipment?

 

[Pacfanweb]

USB could kill someone before something else shorted out from the load? I doubt it.

 

[JohnCU]

Originally posted by: destrekor
Only one of those quotes even brought into question voltage, and that only mentioned voltage like 110v.
Can 500mA at 5v kill a man? I don't think so.
5v at 1.5A? That might be getting into some serious hurt, but I don't think it's going to cause any real harm, but I am not sure at that kind of voltage.

PoweredUSB? That's something I don't think that is found all that often, as it uses extra pins for power delivery? Does this even exist for consumer use, and not just business? Regardless, that's approaching the area where it might very well provide lethal, but again, the voltage I'm not sure. DC requires more amperage, and that is what all computer peripherals operate on (devices that connect only to the PC for power). Voltage is still the question.

Can the max, say 24v at 6A kill a man? That's about the only one I'd say has any potential.

Ever connected a few 1.5v batteries in series and touched the bare wire? It provides a good shock and burning sensation, but other than that no harm. I've done that with a 1.5v batteries, so 4.5v's, at... what's a typical AA battery's amperage? And does amperage increase when in a series? Regardless, at a minimum it's a few hundred mA, but I expect it's more considering rechargeable AAs carry sometimes upwards of 2400mAh (and I'm not extremely knowledgeable in electricity, so if you connected a few 2400mAh batteries in series, what you get on the wire? Any amperage to even speak of? Is the amperage only going to be measurable if it's actually be drawn by electrical equipment?

the voltage doesn't matter. only the current.

 

[PottedMeat]

A quick googling says cardiac tissue has a resistivity of ~175 Ohm-cm. So two needles with 5VDC between them inserted into heart tissue 1 cm apart would get you only 28mA?

http://www.iop.org/EJ/abstract/0967-3334/20/4/201

 

[slackwarelinux]

Originally posted by: PottedMeat
A quick googling says cardiac tissue has a resistivity of ~175 Ohm-cm. So two needles with 5VDC between them inserted into heart tissue 1 cm apart would get you only 28mA?

http://www.iop.org/EJ/abstract/0967-3334/20/4/201

:thumbsup: yep

 

[Evadman]

Originally posted by: JohnCU
the voltage doesn't matter. only the current.

Voltage matters in that you need more than 5 to get any appreciable amperage to flow through your body.

 

[JohnCU]

Originally posted by: Evadman

Originally posted by: JohnCU
the voltage doesn't matter. only the current.

Voltage matters in that you need more than 5 to get any appreciable amperage to flow through your body.

i could think of a couple of ways you could do it. it wouldn't be easy like was said above, but it could be done.

 

[IEC]

Originally posted by: JohnCU

Originally posted by: Evadman

Originally posted by: JohnCU
the voltage doesn't matter. only the current.

Voltage matters in that you need more than 5 to get any appreciable amperage to flow through your body.

i could think of a couple of ways you could do it. it wouldn't be easy like was said above, but it could be done.

But it's still unrealistic.

You'd have to be winning a Darwin award for stupidity to get killed by USB current.

 

[JohnCU]

Originally posted by: Spartan Niner

Originally posted by: JohnCU

Originally posted by: Evadman

Originally posted by: JohnCU
the voltage doesn't matter. only the current.

Voltage matters in that you need more than 5 to get any appreciable amperage to flow through your body.

i could think of a couple of ways you could do it. it wouldn't be easy like was said above, but it could be done.

But it's still unrealistic.

You'd have to be winning a Darwin award for stupidity to get killed by USB current.

yes but i'm sure somewhere in the world someone will try it one day.

 

[destrekor]

Originally posted by: JohnCU

Originally posted by: Evadman

Originally posted by: JohnCU
the voltage doesn't matter. only the current.

Voltage matters in that you need more than 5 to get any appreciable amperage to flow through your body.

i could think of a couple of ways you could do it. it wouldn't be easy like was said above, but it could be done.

okay, it could be done, yes, but voltage matters in that normal, realistic scenarios, without that voltage it's not going to do anything inside your body.

Just like 10,000v but 0.0000001mA isn't going to kill you, but it's gonna deliver one helluva nasty burn. Amperage is indeed all that is needed, but in reality, that amperage isn't getting anywhere without the voltage. Our body will basically diffuse weak voltage, so even if it carries a lot of amperage, that low voltage won't even make it through the body. In anything, only superficially, such as through the tip of a finger or something.

Plugging two wires into chest, well... yeah then voltage basically doesn't matter. But unless you are actually trying to kill yourself... this will happen, when?

 

[Howard]

I think if you stab two steel rods through the heart and then put 5V across them, you could probably die from the current.

 

[JohnCU]

Originally posted by: destrekor

Originally posted by: JohnCU

Originally posted by: Evadman

Originally posted by: JohnCU
the voltage doesn't matter. only the current.

Voltage matters in that you need more than 5 to get any appreciable amperage to flow through your body.

i could think of a couple of ways you could do it. it wouldn't be easy like was said above, but it could be done.

okay, it could be done, yes, but voltage matters in that normal, realistic scenarios, without that voltage it's not going to do anything inside your body.

Just like 10,000v but 0.0000001mA isn't going to kill you, but it's gonna deliver one helluva nasty burn. Amperage is indeed all that is needed, but in reality, that amperage isn't getting anywhere without the voltage. Our body will basically diffuse weak voltage, so even if it carries a lot of amperage, that low voltage won't even make it through the body. In anything, only superficially, such as through the tip of a finger or something.

Plugging two wires into chest, well... yeah then voltage basically doesn't matter. But unless you are actually trying to kill yourself... this will happen, when?

how is 10,000 volts at 0.0000001mA going to give you a burn?

 

[Captante]

Yes its possible.

It is however unlikely in the extreme.

 

[slackwarelinux]

Originally posted by: destrekor
Only one of those quotes even brought into question voltage, and that only mentioned voltage like 110v.
Can 500mA at 5v kill a man? I don't think so.
5v at 1.5A? That might be getting into some serious hurt, but I don't think it's going to cause any real harm, but I am not sure at that kind of voltage.

PoweredUSB? That's something I don't think that is found all that often, as it uses extra pins for power delivery? Does this even exist for consumer use, and not just business? Regardless, that's approaching the area where it might very well provide lethal, but again, the voltage I'm not sure. DC requires more amperage, and that is what all computer peripherals operate on (devices that connect only to the PC for power). Voltage is still the question.

Can the max, say 24v at 6A kill a man? That's about the only one I'd say has any potential.

Ever connected a few 1.5v batteries in series and touched the bare wire? It provides a good shock and burning sensation, but other than that no harm. I've done that with a 1.5v batteries, so 4.5v's, at... what's a typical AA battery's amperage? And does amperage increase when in a series? Regardless, at a minimum it's a few hundred mA, but I expect it's more considering rechargeable AAs carry sometimes upwards of 2400mAh (and I'm not extremely knowledgeable in electricity, so if you connected a few 2400mAh batteries in series, what you get on the wire? Any amperage to even speak of? Is the amperage only going to be measurable if it's actually be drawn by electrical equipment?

Assuming a purely resistive load (sure, why not), the voltage ought to be proportional to the current and resistance by the following equation: voltage = current * resistance. This means the change in any one of these terms will effect one or more of the other ones.

A previous poster cited a paper stating that the resistance of the heart is around 175 ohms/cm. So two leads about a cm apart would see a resistance of 175 ohms. A worst case scenario of the resistance of wet human skin could be around 1000 ohms. Dry skin is closer to 40,000 to 1,000,000 ohms.

With your example of 500ma at 5V, the resistance would have to be 5/.5 or 10 ohms of the circuit. This is an unreasonably low resistance.

With your example of 1.5A at 5V, the resistance would have to be 5/1.5 or 3.33 ohms. This is an unreasonably low resistance.

With your example of 6A at 24V, the resistance would have to be 24/6 or 4 ohms. This is an unreasonably low resistance.

You mentioned the mAh rating of batteries. mAh means milliamp-hour. It is a unit of supply current for a period of time. Ideally, a 2400mAh battery could supply 2.4A for one hour or 240mA for ten hours or 24mA for 100 hours. mAh doesn't have much of anything to do with voltage, it has to do with the capacity of a battery. Both AAA and D cells have the same voltage, somewhere around 1.5 volts. A D cell has a much higher mAh rating than a AAA battery (~10000mAh vs. ~800mAh). The difference is in how long the battery can sustain the current, not how much voltage it puts out.

To answer you question of what you would get if you stuck "a few 2400mAh batteries in series", you would get a voltage that is the sum of the voltage of each cell. Ten 1.2V batteries in series would give you 12V. The mAh rating only changes how long current at that voltage can be sustained for.

To answer your question about measuring amperage, amps are a unit of current, so it could be measured directly by measured the current with an ammeter. Amps are not amp-hours.

"DC requires more amperage, and that is what all computer peripherals operate on (devices that connect only to the PC for power). Voltage is still the question."
Power is equal to current * voltage. DC requires more amperage to deliver the same amount of power only if it is at a lower voltage.


cliffs:
-mAh doesn't matter
-5V likely won't kill somebody by stopping their heart
-go read a book, the art of electronics is an excellent one.

 

[destrekor]

Originally posted by: slackwarelinux

Originally posted by: destrekor
Only one of those quotes even brought into question voltage, and that only mentioned voltage like 110v.
Can 500mA at 5v kill a man? I don't think so.
5v at 1.5A? That might be getting into some serious hurt, but I don't think it's going to cause any real harm, but I am not sure at that kind of voltage.

PoweredUSB? That's something I don't think that is found all that often, as it uses extra pins for power delivery? Does this even exist for consumer use, and not just business? Regardless, that's approaching the area where it might very well provide lethal, but again, the voltage I'm not sure. DC requires more amperage, and that is what all computer peripherals operate on (devices that connect only to the PC for power). Voltage is still the question.

Can the max, say 24v at 6A kill a man? That's about the only one I'd say has any potential.

Ever connected a few 1.5v batteries in series and touched the bare wire? It provides a good shock and burning sensation, but other than that no harm. I've done that with a 1.5v batteries, so 4.5v's, at... what's a typical AA battery's amperage? And does amperage increase when in a series? Regardless, at a minimum it's a few hundred mA, but I expect it's more considering rechargeable AAs carry sometimes upwards of 2400mAh (and I'm not extremely knowledgeable in electricity, so if you connected a few 2400mAh batteries in series, what you get on the wire? Any amperage to even speak of? Is the amperage only going to be measurable if it's actually be drawn by electrical equipment?

Assuming a purely resistive load (sure, why not), the voltage ought to be proportional to the current and resistance by the following equation: voltage = current * resistance. This means the change in any one of these terms will effect one or more of the other ones.

A previous poster cited a paper stating that the resistance of the heart is around 175 ohms/cm. So two leads about a cm apart would see a resistance of 175 ohms. A worst case scenario of the resistance of wet human skin could be around 1000 ohms. Dry skin is closer to 40,000 to 1,000,000 ohms.

With your example of 500ma at 5V, the resistance would have to be 5/.5 or 10 ohms of the circuit. This is an unreasonably low resistance.

With your example of 1.5A at 5V, the resistance would have to be 5/1.5 or 3.33 ohms. This is an unreasonably low resistance.

With your example of 6A at 24V, the resistance would have to be 24/6 or 4 ohms. This is an unreasonably low resistance.

You mentioned the mAh rating of batteries. mAh means milliamp-hour. It is a unit of supply current for a period of time. Ideally, a 2400mAh battery could supply 2.4A for one hour or 240mA for ten hours or 24mA for 100 hours. mAh doesn't have much of anything to do with voltage, it has to do with the capacity of a battery. Both AAA and D cells have the same voltage, somewhere around 1.5 volts. A D cell has a much higher mAh rating than a AAA battery (~10000mAh vs. ~800mAh). The difference is in how long the battery can sustain the current, not how much voltage it puts out.

To answer you question of what you would get if you stuck "a few 2400mAh batteries in series", you would get a voltage that is the sum of the voltage of each cell. Ten 1.2V batteries in series would give you 12V. The mAh rating only changes how long current at that voltage can be sustained for.

To answer your question about measuring amperage, amps are a unit of current, so it could be measured directly by measured the current with an ammeter. Amps are not amp-hours.

Okay, that's what I kind of thought, but it's been awhile since I've studied that kind of material, and my brain is on a lot of other material right now (end of quarter matters, and finals), so I wasn't trying to rack my mind to much.
Yeah, I thought it was amp-hours were just a capacity rating, similar to watt-hours in electrical grid measurement.
I used to know all of this material readily since I was studying in a computer field, and then I switched gears when I hit college and basically stopped trying to remember all that jazz, even with the most simplistic formulas like for current, resistance, voltage, and watts. Ugh, now my brain hurts trying to get that back in there. :laugh:

upon reading your edit:
no I will not go read a book. I'll research it if I ever need it again in life, but at this point, I'm either going to be commanding troops or working security/intel for the government the rest of my life. If I move into computer security and re-train for that field, then I'll have no choice, but till then, I'm set.
And really, I do understand the principals and the equations. I'm just not trying right now. Wrong time to try and remember things that don't apply to tomorrow and next week.

 

[destrekor]

Originally posted by: JohnCU

Originally posted by: destrekor

Originally posted by: JohnCU

Originally posted by: Evadman

Originally posted by: JohnCU
the voltage doesn't matter. only the current.

Voltage matters in that you need more than 5 to get any appreciable amperage to flow through your body.

i could think of a couple of ways you could do it. it wouldn't be easy like was said above, but it could be done.

okay, it could be done, yes, but voltage matters in that normal, realistic scenarios, without that voltage it's not going to do anything inside your body.

Just like 10,000v but 0.0000001mA isn't going to kill you, but it's gonna deliver one helluva nasty burn. Amperage is indeed all that is needed, but in reality, that amperage isn't getting anywhere without the voltage. Our body will basically diffuse weak voltage, so even if it carries a lot of amperage, that low voltage won't even make it through the body. In anything, only superficially, such as through the tip of a finger or something.

Plugging two wires into chest, well... yeah then voltage basically doesn't matter. But unless you are actually trying to kill yourself... this will happen, when?

how is 10,000 volts at 0.0000001mA going to give you a burn?

I exaggerated on the amperage, but electric fences? What is the amperage on those? At volts that high, the amperage has GOT to be low because that voltage is definitely going to run through your body, and if you grab with both hands, right across your heart.

 

[slackwarelinux]

Originally posted by: destrekor

Originally posted by: slackwarelinux

Originally posted by: destrekor
Only one of those quotes even brought into question voltage, and that only mentioned voltage like 110v.
Can 500mA at 5v kill a man? I don't think so.
5v at 1.5A? That might be getting into some serious hurt, but I don't think it's going to cause any real harm, but I am not sure at that kind of voltage.

PoweredUSB? That's something I don't think that is found all that often, as it uses extra pins for power delivery? Does this even exist for consumer use, and not just business? Regardless, that's approaching the area where it might very well provide lethal, but again, the voltage I'm not sure. DC requires more amperage, and that is what all computer peripherals operate on (devices that connect only to the PC for power). Voltage is still the question.

Can the max, say 24v at 6A kill a man? That's about the only one I'd say has any potential.

Ever connected a few 1.5v batteries in series and touched the bare wire? It provides a good shock and burning sensation, but other than that no harm. I've done that with a 1.5v batteries, so 4.5v's, at... what's a typical AA battery's amperage? And does amperage increase when in a series? Regardless, at a minimum it's a few hundred mA, but I expect it's more considering rechargeable AAs carry sometimes upwards of 2400mAh (and I'm not extremely knowledgeable in electricity, so if you connected a few 2400mAh batteries in series, what you get on the wire? Any amperage to even speak of? Is the amperage only going to be measurable if it's actually be drawn by electrical equipment?

Assuming a purely resistive load (sure, why not), the voltage ought to be proportional to the current and resistance by the following equation: voltage = current * resistance. This means the change in any one of these terms will effect one or more of the other ones.

A previous poster cited a paper stating that the resistance of the heart is around 175 ohms/cm. So two leads about a cm apart would see a resistance of 175 ohms. A worst case scenario of the resistance of wet human skin could be around 1000 ohms. Dry skin is closer to 40,000 to 1,000,000 ohms.

With your example of 500ma at 5V, the resistance would have to be 5/.5 or 10 ohms of the circuit. This is an unreasonably low resistance.

With your example of 1.5A at 5V, the resistance would have to be 5/1.5 or 3.33 ohms. This is an unreasonably low resistance.

With your example of 6A at 24V, the resistance would have to be 24/6 or 4 ohms. This is an unreasonably low resistance.

You mentioned the mAh rating of batteries. mAh means milliamp-hour. It is a unit of supply current for a period of time. Ideally, a 2400mAh battery could supply 2.4A for one hour or 240mA for ten hours or 24mA for 100 hours. mAh doesn't have much of anything to do with voltage, it has to do with the capacity of a battery. Both AAA and D cells have the same voltage, somewhere around 1.5 volts. A D cell has a much higher mAh rating than a AAA battery (~10000mAh vs. ~800mAh). The difference is in how long the battery can sustain the current, not how much voltage it puts out.

To answer you question of what you would get if you stuck "a few 2400mAh batteries in series", you would get a voltage that is the sum of the voltage of each cell. Ten 1.2V batteries in series would give you 12V. The mAh rating only changes how long current at that voltage can be sustained for.

To answer your question about measuring amperage, amps are a unit of current, so it could be measured directly by measured the current with an ammeter. Amps are not amp-hours.

Okay, that's what I kind of thought, but it's been awhile since I've studied that kind of material, and my brain is on a lot of other material right now (end of quarter matters, and finals), so I wasn't trying to rack my mind to much.
Yeah, I thought it was amp-hours were just a capacity rating, similar to watt-hours in electrical grid measurement.
I used to know all of this material readily since I was studying in a computer field, and then I switched gears when I hit college and basically stopped trying to remember all that jazz, even with the most simplistic formulas like for current, resistance, voltage, and watts. Ugh, now my brain hurts trying to get that back in there. :laugh:

upon reading your edit:
no I will not go read a book. I'll research it if I ever need it again in life, but at this point, I'm either going to be commanding troops or working security/intel for the government the rest of my life. If I move into computer security and re-train for that field, then I'll have no choice, but till then, I'm set.
And really, I do understand the principals and the equations. I'm just not trying right now. Wrong time to try and remember things that don't apply to tomorrow and next week.

Don't let no foreseeable application knowledge stop you from learning .
The art of electronics is a really is a great example of technical literature.

 

[destrekor]

Originally posted by: slackwarelinux
Don't let no foreseeable application knowledge stop you from learning .
The art of electronics is a really is a great example of technical literature.

No doubt it would be. I do enjoy all fields of learning, at least to a certain extent in comparison to required learning. And electricity is one area which I really find fascinating.

 

[thescreensavers]

Thanks for replying, you all helped me do my homework.. lol just kidding.

But, just wondering since I heard this on a TV show and I knew I smelled Bull