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sleepsleep

Joined: 05 Oct 2006
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sleepsleep
is there any specific reason for the common V set at 5V or 12V?

and what actually that could kill a human?

a high V or a high A?

what is normal human adult limit?
25 Oct 2019, 15:43
revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17287
revolution
To kill a human with electricity you need to care about the current (A).

There is a saying: Volts will jolt, but mills will kill.

Where "mills" is referring to milliamps. If you get enough milliamps across the heart then it can stop beating, or go into fibrillation, or something, and cause lack of blood flow.

So in theory, if you were to get probes directly on the heart, only a few volts is needed to have enough current flowing. But in practice, you'll probably need 100V or more across the hands to get enough current to flow through the heart.

I know many countries classify voltages about 50V as potentially dangerous. If you have wet hands and hold on tightly to 50V I suppose you might get a low enough circuit resistance to allow enough current to flow through the heart. I don't recommend you try it though.
25 Oct 2019, 17:20
sleepsleep

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sleepsleep
ok, the value of A is important,

50V as potential dangerous but at what A value?

is there a relationship formula that define what V must at least equal to what A, or at 50V, the A will never gets lower or higher than what value?

so, even a tiny A, 1A if allowed to pass through our heart without any resistence, we will die?

https://www.theregister.co.uk/2006/10/20/the_odd_body_electrocution/
Quote:
An initial voltage of about 2,000 volts stops the heart and induces unconsciousness.

Quote:
the protocol calls for a jolt of 2,450 volts that lasts for 15 seconds. After a 15 minute wait, the prisoner is then examined by a coroner. After 20 seconds, the cycle is repeated. It is repeated three more times. The body may heat up to approximately 100°C (210°F), which causes severe damage to internal organs. Often the eyeballs melt.

it seems that V is more important, revolution, any idea?

but why death punishment through poison not in consideration?
25 Oct 2019, 21:31
revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17287
revolution
We don't know what current will flow. You have to make a circuit and the human body is not an ideal conductor. The skin varies in conductivity. The connection resistance is variable. etc. So there are a lot of unknowns.

In ideal conditions 50V could be enough. Wet hands, well hydrated body, whatever else is needed to make a good connection across the hands, then you could get a lethal current flow.

I have seen values of 30mA as enough to affect the heart.

If you are talking about deliberate execution then they would use very high voltages to make sure everything goes as planned. They wouldn't use 50V and hope for all the best other conditions. They want to do it once and then finished.

Also note that you could have 1000V across the feet and the current might never pass through the heart so the person might still live. But I imagine they would be badly injured and could suffer paralysis or lose their limbs.

Alternatively you could have 1000V across the hands, but have very dry hands, and be dehydrated, etc, and perhaps the current flow through the heart only gets to 10mA.
26 Oct 2019, 01:41
sleepsleep

Joined: 05 Oct 2006
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sleepsleep
ok, i guess for me to better understand this concept, perhaps is it possible for you to fit the idea of V and A in the following scenario?

"i am pushing a stationary toy car from its current spot to another 1 meters."

1. what is that called inside my human body that able to push this car? which will decrease after i use them, like laptop battery,

2. i could push this toy car instantly (very fast, near bullet speed) or i could push it very slow even if i got the POWER to move it faster

3. a stucked or glued toy car might represented resistance i guess,
26 Oct 2019, 07:23
revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17287
revolution
sleepsleep wrote:
1. what is that called inside my human body that able to push this car? which will decrease after i use them, like laptop battery,
Energy.
sleepsleep wrote:
2. i could push this toy car instantly (very fast, near bullet speed) or i could push it very slow even if i got the POWER to move it faster
Same total energy used, just using a different release time. High power fast energy release.
sleepsleep wrote:
3. a stucked or glued toy car might represented resistance i guess,
I think friction might be a better analogy. The wheels don't turn and you have to slide it across the surface. Different wheel compositions and different surfaces give different friction values.
26 Oct 2019, 07:32
st

Joined: 12 Jul 2019
Posts: 43
Location: Russia
st
sleepsleep wrote:
is there any specific reason for the common V set at 5V or 12V?

12V comes from the lead acid battery technology (6 cells * 2V = 12V).

5V is old TTL-chips standard https://en.wikipedia.org/wiki/Transistor%E2%80%93transistor_logic#Interfacing_considerations (calculated from transistors characteristics)

Last edited by st on 26 Oct 2019, 09:28; edited 1 time in total
26 Oct 2019, 07:40
sleepsleep

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sleepsleep
revolution wrote:
sleepsleep wrote:
1. what is that called inside my human body that able to push this car? which will decrease after i use them, like laptop battery,
Energy.
sleepsleep wrote:
2. i could push this toy car instantly (very fast, near bullet speed) or i could push it very slow even if i got the POWER to move it faster
Same total energy used, just using a different release time. High power fast energy release.
sleepsleep wrote:
3. a stucked or glued toy car might represented resistance i guess,
I think friction might be a better analogy. The wheels don't turn and you have to slide it across the surface. Different wheel compositions and different surfaces give different friction values.

where is V and A ?

i think my desire to push that car is equal to nature of negative that wanted to flow to positive, am i correct?
26 Oct 2019, 08:33
gens

Joined: 18 Feb 2013
Posts: 161
gens
Voltage is the difference of electric potential between two points. It's a force.
Amperes are the amount of current passing through something (a wire). It's electrons, more specifically their charge.

How strongly you push the car would be the Voltage. How fast the car goes would be the Amperage.
The 1A and 2.5A would be how fast you can go, as in your speed limit. Pushing the car faster might give you a heart attack.

PSU-s and other such supplies of power are "constant voltage supplies", because the Voltage is.. constant.
The load dictates the amount of current, in this case.
I = V / R
I is the current in Amperes, V the voltage in volts, and R the resistance in Ohms. (Ohm's law)

You can use these ratings to calculate how much power it can put out.
P = V * I
12V at 2.5A gives 30W. (P is power, in Watts)

For some things (like big-ish electric motors), there are a couple of other things to consider.

PS PSA

50mA going through your heart will stop it.

If you touch one wire with one hand and the other wire with the other hand, much of the current will go over your heart. (and if you touch one wire with your foot and the other with the other foot..)
Path of least resistance.

If you grab a "high" voltage wire, your hand will clench and you won't be able to let it go (high voltage for us, but 110/220V AC is really "low" voltage). If you have to touch a wire (or anything) that you think might be electrified, do it with the outside of your hand or something.

If a high voltage wire (power line, 10000V AC, much hertz) falls to the ground really close to you, do not walk towards or away from it. Feet together and hop away, some ~10 meters away from it at least.
04 Jan 2020, 12:42
sleepsleep

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sleepsleep
https://www.thespruce.com/amperage-not-voltage-kills-1152476
Quote:

some experts use an analogy of a flowing river to explain the principles of electricity. In this analogy, voltage is equated with the steepness, or pitch, of the river, while amperage is equated with the volume of water in the river. An electrical current with high voltage but very low amperage can be seen as a very narrow, small river flowing nearly vertical, like a tiny trickle of a waterfall. It would have little potential to really hurt you. But a large river with lots of water (amperage) can drown you even if the speed of flow (voltage) is relatively slow.

A to volume of water, and V to steepness, i think this is very good analogy,

Quote:
If let say I got a device with input Power: 12V === 1A

Could I use adaptor with Output: 12V === 2.5A

What are the effect, issues concern with using adaptor with different V or A ? higher or lower ?

push 2.5A water, but input only allow 1A water, where the extra 1.5A water goes?
04 Jan 2020, 13:55
DimonSoft

Joined: 03 Mar 2010
Posts: 707
Location: Belarus
DimonSoft
gens wrote:
Feet together and hop away, some ~10 meters away from it at least.

Actually I’ve heard jumping is not really safe. What if you fall? For the same reason it’s not recommended to jump-run: while you won’t touch the ground with both feet simultaneously, you’ll be in danger of falling. AFAIK, the safest way is to make tiny “steps” keeping feet together and touched to the ground.
04 Jan 2020, 19:30
gens

Joined: 18 Feb 2013
Posts: 161
gens
DimonSoft wrote:
gens wrote:
Feet together and hop away, some ~10 meters away from it at least.

Actually I’ve heard jumping is not really safe. What if you fall? For the same reason it’s not recommended to jump-run: while you won’t touch the ground with both feet simultaneously, you’ll be in danger of falling. AFAIK, the safest way is to make tiny “steps” keeping feet together and touched to the ground.

You can shuffle as well, make tiny steps. Point is to not have a "big" distance between your legs, relative to where the cable lies.

Most important thing is, of course, to not panic.
15 Jan 2020, 09:56
revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17287
revolution
sleepsleep wrote:
https://www.thespruce.com/amperage-not-voltage-kills-1152476
Quote:

some experts use an analogy of a flowing river to explain the principles of electricity. In this analogy, voltage is equated with the steepness, or pitch, of the river, while amperage is equated with the volume of water in the river. An electrical current with high voltage but very low amperage can be seen as a very narrow, small river flowing nearly vertical, like a tiny trickle of a waterfall. It would have little potential to really hurt you. But a large river with lots of water (amperage) can drown you even if the speed of flow (voltage) is relatively slow.

A to volume of water, and V to steepness, i think this is very good analogy,

Quote:
If let say I got a device with input Power: 12V === 1A

Could I use adaptor with Output: 12V === 2.5A

What are the effect, issues concern with using adaptor with different V or A ? higher or lower ?

push 2.5A water, but input only allow 1A water, where the extra 1.5A water goes?
Amperes is a measure of flow rate, not volume, so the question isn't valid. It is like asking: your car can do 100km/h but you only drive at 30km/h so where does the other 70km/h go?
15 Jan 2020, 12:28
bitRAKE

Joined: 21 Jul 2003
Posts: 2915
Location: [RSP+8*5]
bitRAKE
The classic example of household electrocution is "standing in water and touching metal" - I've experienced this multiple times. The leak to moisten the floor can be anything: plumbing problem, bad fridge, etc. Old houses often don't have proper ground or through several renovations the ground is unreliable. Metal railing, stove, light fixture ... seemingly benign activities can result in tragedy. This is also a frequent cause of house fires.

_________________
15 Jan 2020, 23:42
sleepsleep

Joined: 05 Oct 2006
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sleepsleep
A is flow rate (which could be imagined as size of water tube) and V is the differentiation in point A to point B which try to seek balance, am i correct?

input 12V 1A could accept output 12V and above 1A, because output could adjust a higher A into 1A, like driving 30km/h although the car could goes 150km/h,

but how come that website use voltage as speed is flow? and A as volume?
16 Jan 2020, 02:09
revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17287
revolution
If you want to use water as an analogy:

Flow rate is not the same as the tube size. Flow rate is how much the consumer is taking. Tube size is the maximum rate that can be delivered. You can have a large tube size but no flow rate because there is no consumer connected.

Voltage would be the pressure.
Current would be the flow rate.

A producer device (a PSU) will manage the pressure, not the flow rate.
A consumer device (a laptop) will manage the flow rate, not the pressure.
16 Jan 2020, 02:26
Furs

Joined: 04 Mar 2016
Posts: 1471
Furs
Yeah it's like turning the knob on your kitchen sink. You control the amount of water that goes through (this is the consumer).

Obviously your pipe isn't going to change size...
16 Jan 2020, 18:46
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