Volts vs Amps

Status
Not open for further replies.
Russell Ensslin

Russell Ensslin

Member
Location
Olivehurst California
So I have a lot of trouble trying to get my head around the concept of volts vs. amps. I've heard the water pressure vs amount available concept but that doesn't seem to work with many examples. Youtube has good ones about rocks that fall but from different heights but that doesn't explain how a 9V battery tickles your tongue but a 6V truck battery has enough amps to kill you!
I was trying to use the concept of the strong body-builder laborer who can't do much work because he gets hungry too quickly, of has no skills.
Or the concept of the really hot super sexy babe but she is totally frigid; you know, all volts but no amps. \
Does anyone have good links? about volts/amps I mean?
 
Z

zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
Russell Ensslin said:
but that doesn't explain how a 9V battery tickles your tongue but a 6V truck battery has enough amps to kill you!
Click to expand...

Ah, but a 9v battery does have enough amps to kill you if connected in the wrong place! So does a flashlight battery (it doesn't take much). And if you have dry hands and touch the terminals of the truck battery, you might not even feel it.

To make sense of this, add in the concept of resistance- ignoring static electricity, you can't have current (amps or flow) without something making a full circuit and pushing back on the flow (ohms or resistance). When you have a flow through a resistance, it is now possible to measure a potential difference across that resistance, and that gives us voltage. Even a voltmeter has a very small current flow through it and completes a circuit (through the meter).

A higher voltage is more dangerous because it has more ooomph to push through the same resistance to get a dangerous current.

Voltage = current times resistance
or
Current = voltage divided by resistance

Hope that helps, it was rather spur-of-the-moment writing and it's past my bedtime :).
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
It is a cliche, but still a serviceable analogy:
Voltage is like water pressure and current is like water flow.
A battery is like an elevated tank which is characterized by three things.
Height (voltage)
Volume (capacity in amp-hours) and
Size of outlet pipe (internal resistance)
Your 9 volt battery is a very small high tank with small outlet.
Your 6V truck battery is a lower larger tank with a large outlet.
The pressure of the 6V battery will not hurt you directly, but it can drown you.(a short circuit, not through, you causing burns, etc.)

The weakest part of the analogy is that electric current requires a closed path while water flow does not.
 
J

JFletcher

Senior Member
Location
Williamsburg, VA
Neither a 6V truck battery nor 9V clock battery is likely to kill you, however that's because your body's resistance to current flow is generally high enough (at those voltages) to prevent a fatal amount of amperage to stop your heart, and it's also unlikely the current would travel across your heart.

Now, if you take a conductor with very low resistance (say a solid copper bar) and touch the terminals, the 9V battery will give a little spark, whereas a truck battery would produce a large spark and could very well weld the conductor to the terminals and self-destruct. This is because the truck battery has a much larger capacity than the clock battery.

Voltage is potential for flow of electricity; amperage *is* flow of electricity. A 50,000V stun gun just hurts because it's powered from that same 9V clock battery, and is limited by other factors such as wire size and internal resistance of the battery. A 50,000V lightning strike (or 50,000V power line) isnt nearly as limited as the stun gun; you can have 10s of thousands of amps flowing thru a lightning arc, and just as many thru a transmission line during a fault before the fault clears (or the conductors self-destruct)

Amperage is what kills you.

You can also think of amperage as mass or size, and voltage is speed. Say you have a grain of sand moving 300mph (EF-5 tornado), and a brick moving the same 300mph. Getting hit by the grain of sand will sting; getting hit by the brick would probably dismember you. The grain of sand is the 50kV coming from a stun gun, the brick the lightning strike.

If you wanted to compare to water, amperage is volume and voltage is pressure/speed. Think of the difference between a cup of water being dumped onto you from 167' up vs being under Niagra Falls (also 167' high). Low amperage vs high amperage.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
JFletcher said:
Amperage is what kills you.
Click to expand...


It is never just the volts that kill, it is never just the amps that kill

It is the combination of both so let's stop trying to assign just one of those things as the cause of death.


What lights up a light? Is it amps or voltage?
 
ActionDave

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
iwire said:
It is never just the volts that kill, it is never just the amps that kill

It is the combination of both so let's stop trying to assign just one of those things as the cause of death.


What lights up a light? Is it amps or voltage?
Click to expand...
:thumbsup: It's time we burried that amps kill you thing and stomp the dirt down on top of it.
 
Besoeker

Besoeker

Senior Member
Location
UK
Smart $ said:
Technically, electric current... in order to separate this phenomenon from fluid current............
Click to expand...
Quite.
But, given that this is an electrical forum, I think it would not be unreasonable to assume that electric current is what is intended here rather than an allusion to The Gulf Stream or the flow of water over the Angel Falls.
So, I think the qualification isn't all that smart.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Besoeker said:
Quite.
But, given that this is an electrical forum, I think it would not be unreasonable to assume that electric current is what is intended here rather than an allusion to The Gulf Stream or the flow of water over the Angel Falls.
So, I think the qualification isn't all that smart.
Click to expand...

Ok so this is just like the other day in another thread.

In the other thread you brought up the OPs question like it was relevant and then I brought up the OPs question and you told me it was not relevant.

In this thread you decided to nit pick a word used but when someone nit picked back you say we should know. :roll:
 
rambojoe

rambojoe

Senior Member
Location
phoenix az
Occupation
Wireman
it is best to ask the plumbers about theory, after all its their "forte" :) how come no one uses the water wheel and river "head" analogy?
 
S

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
iwire said:
It is never just the volts that kill, it is never just the amps that kill

It is the combination of both so let's stop trying to assign just one of those things as the cause of death.


What lights up a light? Is it amps or voltage?
Click to expand...

I disagree with you. (even though you are a moderator and I am a lowly subscriber.:)) The intention of that statement is to clarify that current flow is the predominate factor in electrocution. I don't feel it is meant as a warning for the average citizen, it is meant for the electrician, so that he may understand the true dangers when working around electricity. All other factors aside, the amount of amperage and the path it takes through the body, combined with the luck and resilience of the person being shocked are the factors. It could be 100,000 volts from a door knob, and just really irritate you, without effect, or it could be 50-60 volts in the right circumstances like direct contact with salty blood, that kills you. It is 100ma or more through your heart.
 
S

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Russell Ensslin said:
So I have a lot of trouble trying to get my head around the concept of volts vs. amps. I've heard the water pressure vs amount available concept but that doesn't seem to work with many examples. Youtube has good ones about rocks that fall but from different heights but that doesn't explain how a 9V battery tickles your tongue but a 6V truck battery has enough amps to kill you!
I was trying to use the concept of the strong body-builder laborer who can't do much work because he gets hungry too quickly, of has no skills.
Or the concept of the really hot super sexy babe but she is totally frigid; you know, all volts but no amps. \
Does anyone have good links? about volts/amps I mean?
Click to expand...

Just my opinion, but until you understand the comparison between water and electricity, I don't think you will start to grasp electrical theory. The analogy is very basic, but also easy to grasp because it is easy to observe. Voltage is pressure, amperage is flow, and resistance is restriction or resistance to the flow. Not resistance to the flow, not resistance to voltage, but flow. The thing is, you don't want to make it too complicated, you are just trying to visualize how the three factors interact with each other. If you want to use a fluid analogy that has more comparable analogy, you can use a closed loop hydraulic system, but the visualization is a little harder.

While your statements about a 9v and 6v battery aren't entirely accurate, they can still be marginally visualized with water. If you have a 1/2" pipe with 3 pounds of pressure (9v battery as in higher voltage, but more restriction to flow), filling your pool, vs. a 20" pipe with 1 pound of pressure (6V battery) filling your pool, which one is going to fill up your pool faster? Or if you need to put it in amount of damage terms, which one will wash away a kitten faster? Again, not perfect, because batteries have one more factor that you are not taking account and that is capacity.
 
Besoeker

Besoeker

Senior Member
Location
UK
iwire said:
Ok so this is just like the other day in another thread.

In the other thread you brought up the OPs question like it was relevant and then I brought up the OPs question and you told me it was not relevant.

In this thread you decided to nit pick a word used but when someone nit picked back you say we should know. :roll:
Click to expand...
I didn't say you should know.
 
K8MHZ

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Russell,

The volts vs. amps is a common question with a zillion different interpretations of the answers.

Let's start with some observations.

Current can be measured at one point. It is the electrons passing that single point. It is a rate, like miles per hour.

Voltage must be measured at two points. It is the difference in the amount of electrical potential between two points. Voltage is not a rate. Voltage does not involve movement.

When we design wire, if we want the wire to handle a lot of current, that conductor must be large enough to handle the high rate of moving electrons. If we want the wire to handle a lot of voltage, we need 'lots' of insulation to keep the voltage differences between the metal wire and it's surroundings where they are supposed to be.

If we have a circuit fed by wiring as we know it, and we look at the wire, we need the insulation any time the power to the wire is turned on. Even if there is no load and no current, the insulation is needed due to the presence of voltage. The insulation is independent of the current. For example, the large wire going to a car starter, which doesn't need 600 volt insulation to be safe. We don't up size the metal part of wiring for voltage.


When current starts to flow, we need a sufficient path for that, so the metal part of the wiring must be up sized. We can make the metal part of the wire HUGE for 1000's of amps, an so long as our design voltage isn't changed, we use the same insulation for 10 amps at 240 volts as we do for 1000 amps at 240 volts.

Is any of this making sense?

I try to stay away from water type analogies as there are always little things about them that don't follow true.

Don't give up trying to understand the difference between volts and amps because we may not be explaining it in the best manner for you. This is a basic concept and please feel free to ask as many questions as it takes to help you understand.
 
Last edited:
Status
Not open for further replies.
Top