voltage,current, relationship!?

[Beginner!?]

hi there

i dont know if here is a good place to talk about this topic or no

but really what is relationship between V and I ?

i thinnk this i better i say what is voltage and what is current?

how do you make a voltage limiter with a resistor(or any else thing)and it works without changing at the currecnt rate? and how do you make a current limiter and it changes the current without any change at the voltage?

i think i am very confused about V & I

thanks for any help :)

[slipstick]

The relationship between V and I depends on what they're operating across. For a fixed resistance it's very simple and is called Ohms Law.

V = I * R or I = V / R

But that doesn't help much in the real world where most things aren't fixed resistors.

There are many good books and websites on basic electricity and electronics which will give you more information. http://www.epanorama.net/links/basics.html is a good place to start.

Steve

[Beginner!?]

thanks Steve for your help

but i dont know even what voltage and current are really

i know ohm's law but i cant see other things about

[Acetronics]

Hi, beginner

Lest's do a comparison ...

think to a dam :

Water level is Voltage : the more you have, the more power you can get.
Water flow is current : depends on what it goes through ... and depends of water level.
High resistance ( or impedance ) is the small hole, low resistance the big hole ...

you can play with water level and/or hole diameter ... flow follows.

Alain

[Beginner!?]

Alain,
thanks for your clearness
the water comparison is a good thing to find out the V and I

i thought perhaps my answer must need for a large of paragrafs so no one try to give me an answer,but your answer was samall and effective

here's my opinion after reading your post(please correct me if it is wrong)

voltage is the RATE of electrons at the source.

current is flow(move) of these electrons.

battery resistance?? i dont know yet

battery power = rate of electrons X the number of electrons when they move from the power sorce to the circuit

but why a sorce can give more current than other with the same voltage (for example a 12V car battery and a dry 12 V battery bothe can give 12V but with a lot of difference at the output current?)

can anyone answet my other question about voltage limiters and current limiters?


thanks

[Beginner!?]

perhaps power source resistance is a smal current that moves(flow) from positive source to negative at idle power position?if so,but why!?

[Acetronics]

Hi,

;) I'd better compare voltage to pressure ... as the higher the level, the higher the pressure.

flow = constant coefficient x section of hole x SQR ( 2 x g ( gravity = 9.81 ) x h ( water heigh upon the hole ) )

as it means internal power source impedance is a view of mind to simplify the parasitic resistance to current flow existing in a battery or generator.

The small current inside the battery, you're talking about is probably the leakage current.

:confused: But why do you talk about Idle position ???

Alain

[Norman Adlam]

Alain,
thanks for your clearness
the water comparison is a good thing to find out the V and I

i thought perhaps my answer must need for a large of paragraphs so no one try to give me an answer,but your answer was small and effective

here's my opinion after reading your post(please correct me if it is wrong)

voltage is the RATE of electrons at the source.

current is flow(move) of these electrons.

battery resistance?? i dont know yet

battery power = rate of electrons X the number of electrons when they move from the power source to the circuit

but why a source can give more current than another with the same voltage (for example a 12V car battery and a dry 12 V battery both can give 12V but with a lot of difference at the output current?)

can anyone answer my other question about voltage limiters and current limiters?

thanks

Beginner,

Just helped 'tweak' the spelling etc above :D

Anyway - voltage is the 'pressure' trying to push the electrons through a given material. In the Dam (water) example it's the height of the water, trying to force the water along - NOT the rate! (From this you might start to surmise that as you 'dam' the flow then the pressure (voltage) will increase, and if you release / increase the 'flow' then the pressure could drop.

Current is the 'flow rate' of electrons - how many electrons / second are passing by (how many gallons / minute for water)!

Resistance is exactly that - how much 'force' tries to prevent the flow from passing along. It's applicable to everthing - in case you are getting confused with your 'battery resistance' question. Think of the resistance of ice to prevent a sliding force, compared with the resitance of rough concrete to a sliding force!

Battery power = the force available to push the electrons x the number of electrons actually moving.

The reason why one battery has more 'power' than the other is that (if they were buckets of water of small and large size), if they are placed at the same height - they both have the same pressure (due to gravity) forcing the water along, but one has physically smaller capacity, so can't keep it up for very long! The batteries are the same.

We'll answer your other questions in a mo!

Hope that helps! :)

Cheers,

[Acetronics]

Voltage and current limiters ...

Voltage limiter ... back to the dam.
Just stop or reduce filling the dam when pressure is sufficient.
Electrically add a variable resistor ( a transistor ) in series in the circuit to create a voltage drop in the supply section.

Current limiter ... back ...
Add a servo to reduce the hole if flow is too high ... or limit the water level.
Electrically add a variable resistor in series in the circuit to enhance the total resistance ... as you feel, it can be placed everywhere in the circuit and can be done by the same transistor as in voltage limitation case ... ( the two effects add to themselves )

Alain

[Beginner!?]

Alain.
my mean about idle positon and the its resistance was the leakage current.
i couldnt call it from my mind again(my poor english)

you talked about a hole at the dam and said it is resisance so i thought it is the battery resistance (inside resistance)

[Beginner!?]

Beginner,

Just helped 'tweak' the spelling etc above :D

Anyway - voltage is the 'pressure' trying to push the electrons through a given material. In the Dam (water) example it's the height of the water, trying to force the water along - NOT the rate! (From this you might start to surmise that as you 'dam' the flow then the pressure (voltage) will increase, and if you release / increase the 'flow' then the pressure could drop.

Current is the 'flow rate' of electrons - how many electrons / second are passing by (how many gallons / minute for water)!

Resistance is exactly that - how much 'force' tries to prevent the flow from passing along. It's applicable to everthing - in case you are getting confused with your 'battery resistance' question. Think of the resistance of ice to prevent a sliding force, compared with the resitance of rough concrete to a sliding force!

Battery power = the force available to push the electrons x the number of electrons actually moving.

The reason why one battery has more 'power' than the other is that (if they were buckets of water of small and large size), if they are placed at the same height - they both have the same pressure (due to gravity) forcing the water along, but one has physically smaller capacity, so can't keep it up for very long! The batteries are the same.

We'll answer your other questions in a mo!

Hope that helps! :)

Cheers,

but what i guessed to now was that the pressure is power source ability to give us more current(more electrons can flow with more pressure) so i thought this pressuer is a thing in relate to current

what you said about height of the water for larger and smaller battery with the same voltage i can not see what is the HEIGHT at the battery?

[Beginner!?]

Voltage and current limiters ...

Voltage limiter ... back to the dam.
Just stop or reduce filling the dam when pressure is sufficient.
Electrically add a variable resistor ( a transistor ) in series in the circuit to create a voltage drop in the supply section.

Current limiter ... back ...
Add a servo to reduce the hole if flow is too high ... or limit the water level.
Electrically add a variable resistor in series in the circuit to enhance the total resistance ... as you feel, it can be placed everywhere in the circuit and can be done by the same transistor as in voltage limitation case ... ( the two effects add to themselves )

Alain

my mean about limiter was how this is possible limiting the voltage or current WITHOUT the other value( voltage or current) changes

thanks all friends for your helps and clearness :)

[Norman Adlam]

but what i guessed to now was that the pressure is power source ability to give us more current(more electrons can flow with more pressure) so i thought this pressuer is a thing in relate to current

what you said about height of the water for larger and smaller battery with the same voltage i can not see what is the HEIGHT at the battery?

Beginner,

And guess what - you are correct! :p

The higher the pressure the higher the flow (increase V then you get an increase in I - assuming the resistance doesn't change). The only difference is that current is related to pressure (voltage) - without a voltage difference you can't get any current to flow.

The height of the larger battery is 'how many electrons it can pack into the available space'. Different battery chemistries can 'pack' more electrons than other ones - so you may hear a phrase such as 'current density' used.

Any better?

Cheers

[Acetronics]

;) Hi, beginner,

If you want to go a little further, may be more, there's a site to visit:
http://www.facstaff.bucknell.edu/mastascu/eLessonsHTML/TOC_BasicConcepts.html

Regards

Alain

:p For others, the ( start ...) gate is here:
http://www.facstaff.bucknell.edu/mastascu/eLessonsHTML/EEIndex.html