ohms law tutorial

Rocketman · 08-04-2011, 11:37 PM

This is publication that I learned about electricity and ohms law, only a much older edition (1960). There is a lot of knowledge in this publication.

Learn the basics.

http://www.arrl.org/chpt-3-electrici...nents-circuits
You can find used copies on ebay or some of the used book sites for $10 to $20 or so. It is written for anyone from beginner to experimenter.

Post 9: Blue LED, 150 ohms = 6.7 ma max @ 4.23V,

Post 27 Answer Key:
A 2.0A, 7.2W.... 1.6A, 5.8W.... 1.2A, 4.3W
B 2.8A, 14W.... 2.3A, 11.5W.... 1.7A, 8.5W
C 2.4A, 10.3W.... 2.0A, 8.6W.... 1.4A, 6W

hagstrom · 08-05-2011, 12:18 AM

or just use this

http://www.ohmslawcalculator.com/ohm...calculator.php

Rocketman · 08-05-2011, 01:02 AM

hag,
that's why people don't understand ohm's law. A calculator is like listening to your GPS tell you "turn left here" as a substitute to learning geography or reading a map.

An ohm's law calculator multiplies and divides, but what do you really learn?

hagstrom · 08-05-2011, 01:22 AM

Quote:

Originally Posted by Rocketman

hag,
that's why people don't understand ohm's law. A calculator is like listening to your GPS tell you "turn left here" as a substitute to learning geography or reading a map.

An ohm's law calculator multiplies and divides, but what do you really learn?

I wont argue that point ! , it is really a simple relationship between 3 variables voltage , current and resistance .

Rocketman · 08-05-2011, 01:35 AM

You would think that people would be eager to learn something new. But they get used to short cuts. I see time after time over on the big forum, someone that starts out building a mod that is way over there head then expects someone to tell them what size resistor to use with an led in a VV boost mod.

What in the world did they expect? I like to help folks out, but sometimes you can tell they are just lazy and want someone to do the work for them.

Folks, don't be afraid to learn. If you can't find out something on the internet, buy a book with some of your e-juice "flavor'' money.

Failure to learn,

OK, ranting over,
Rocky

hagstrom · 08-05-2011, 02:06 AM

LMAO Ya no kidding !

Flashwitt · 08-05-2011, 02:41 AM

I don't MAKEthings... I VAPE things.

Flashwitt · 08-05-2011, 02:47 AM

I should add to the half-sarcastic remark, Rocky, I consider deliberate ignorance to be the only unforgivable sin. However, I do not believe that everyone must know EVERYthing. Ergo: Just because you like sandwiches doesn't mean you need to become a baker, or a butcher, or farm your own hydroponic tomatoes. Nothing wrong wth learning a little science, but some of our brains really are skewed upon a different vector, and fail to grasp Ohms Law no matter how many times we are told. So. I am going to go right on vaping things, even if I don't know how to build 'em. ;D

Rocketman · 08-05-2011, 03:45 AM

Sometimes it would be handy to just know what carto resistance will work with a particular e-cig and maybe have an idea before you fry a carto or battery if it will actually give the desired results. I understand that it is NOT NECESSARY to know how to figure some of these things out. Many have gone before you and posted their results on Youtube

To each his/her own

How about some
FUN WITH OHM'S LAW?

Rocketman · 08-05-2011, 03:48 AM

Let’s put ohm law to a practical application in a DIY e-cig mod.

I want to have a Blue LED that will work with a maximum voltage or 4.23 volts (and not burn out) and not light when cell voltage under load is less than 3 volts. That sounds sort of handy for a 3.7 volt mod, but can it be done?

The typical Blue LED is rated for 20ma continuous current (about 30ma for a 1 second pulse) but will burn out in short order at more than that. The turn on voltage (just starts putting out light) is about 3.1 volts, and is conducting the rated 20ma at about 3.4 volts. As voltage goes above the 3.1 volt turn on point current goes up and it would burn out almost instantaneously at 4.23 volts. Sounds like we might need a resistor. Even though there is a conduction “curve” with an LED let’s just assume a linear response from 3.1 to 3.4 volts of about 6.7ma for each tenth of a volt above 3.1 (a slope of 67ma/V)
3.1v=0ma
3.2v-6.7ma
3.3v=13.4ma
3.4v=20.1ma

A quick search of the mod threads seems to indicate 470 ohms is the resistor to use with an LED. That’s what everyone sells for LEDs. So, let’s test this theory with the desired 4.23 to 3 volt range. I see one problem right off the bat. The Blue LED probably won’t come on at 3.0 volts. Let’s call in the ohms police to see what really will happen.

The highest voltage the LED will ever see in a 3.7 volt mod is 4.23 volts with a fresh off the charger cell, and no atty/carto (maximum unloaded voltage) =V(LED)+V(resistor)=4.23
V(LED)=(3.1) + (ma/67)
V(resistor)=(470 X A) / (1000ma/A)
0.470ma + ma/67 + 3.1 = 4.23
ma (0.470 +0.014925) = 1.13
ma = 1.13/0.4849 = 2.23 ma at 4.23 Volts (3.135 V across LED, 1.095V across Resistor).
With an atty connected most mods will deliver about 3.7 volts.
The current through the LED will be about
0.470ma + ma/67 + 3.1 = 3.7v
ma (0.470 +0.014925) = 0.6
1.24ma at 3.7volts (loaded)
With a loaded voltage of 3.2 the current through the LED and resistor will be about 0.2ma
Rather dim.
This resistor/LED combination, maybe a little on the dim side, would not light up with a loaded voltage of 3.1 or less. A current of about 5 to 10ma at full charge/no load might be better.

I’ll leave it up to the modder to calculate the resistor for a little brighter Blue LED, or a Red LED (turn on about 1.7 volts, 20ma at about 2.0 volts) or a Green LED (turn on about 2.1 volts, 20ma at about 2.4 volts).

Isn’t this fun?

berger · 08-05-2011, 05:55 AM

Thanks Rocky,
as always for pointing us math dyslexic in the right direction to learn how to do this ourselves...was about to run head long into this problem..
thread stuck...(so I can find it in again...

)

RY4 · 08-05-2011, 07:48 AM

Always fun with Rocket's Science

Thanks Rocky. It is always good to learn something. Can't believe I will try to post this while under pain meds... but what I know and how I learned about ohm law:

When I learned about Ohm's Law, I had to compare electrons flowing through a wire to that of water flowing through a pipe. The numbers used to describe the flow of electrons in an electric circuit is the same as the amt. of water that passes a point each second and the pressure behind it. The current (# of electrons) that flows in a wire is measured in amps. 1 amp corresponds to a flow of 1 coulomb (unit of electrical charge) per sec past a point in the wire. Therefore, electrical current is analogous to the current of a river. Most households use from 1 amp (100 watt bulb) to 40 amps (stove with all burners going).

The pressure produced by an energy source in a circuit is the voltage, measured in volts (V). Volts can be thought of in the same way as the water pressure in your plumbing system. More volts, more oomph to the current, just as more pressure makes water flow faster. Most household circuits operate on either 115 or 230 volts.

Wires through which the current (electrons) flow are analogous to pipes carrying water. The smaller the pipe, the harder it is to push water through. Similarly, it is harder to push electrons through some wires than others. How hard it is to push electrons through wires is called electrical resistance and is measured in a unit called the ohm. The higher the resistance, the more electron energy that is converted into heat. Copper wire has low resistance which is why it is used in most households. (Can ya tell I had to go through the stages of building a house-- hehehe). Toaster ovens/space heaters employ high-resistance wires so they will produce large amts of heat when current flows through them.

Voltage (Electrical Pressure) => Water Pressure
Resistance (Resistance to Electron Flow) => Pipe Diameter
Current (Rate of Electrons) => Flow Rate
Power (Current x Voltage) => Rate of Work Done by Moving Water

Power (Watts) = Current (Amps) x Voltage (Volts)

or

Current = Power/Voltage

The people behind electric circuits are more interesting to me though. Galvani's frog experiment is very interesting as well as Volta's arguments against it and his work leading to the development of the battery.

Ok, I'm worn out now. Any errors here are due to the effect of drugs in my system.... blahahaha.

berger · 08-05-2011, 10:07 AM

damn...doesn't read very blonde...

CountryCarolyn · 08-05-2011, 10:14 AM

I'm not lazy. I am actually one of those that don't mind learning. Sometimes it might take a minute for the light bulb to go off. Once it does watch out!

I can imagine that there is few that read ohms law the first time and understood it perfect without any previous knowledge of electricity other than don't stick your finger there cause it will shock you.

berger · 08-05-2011, 10:31 AM

I think the thing that got me started thinking about it when I was young and went with my Dad to the auto parts place when he was getting a new battery for the car..I remember thinking 750 amps!!...damn thats a lot when all the breakers in your house is mostly 15 amp breakers...with that much power what in the heck is the gasoline for?? ....LOL

Rocketman · 08-05-2011, 10:49 AM

I am sorry if it sounded like I was putting you guys down, but Please, unless you want to keep buying and killing cartos and mods learn just a little about how these things work on the "inside". Many times a little 'mental troubleshooting' will save the day when a battery acts up or you just can't seem to make things work right. For those that want to DIY, it's really important.
(RY, R is an inverse relationship to PD

)

Flashwitt · 08-05-2011, 12:14 PM

Quote:

Originally Posted by RY4

...
The pressure produced by an energy source in a circuit is the voltage, measured in volts (V). Volts can be thought of in the same way as the water pressure in your plumbing system. More volts, more oomph to the current, just as more pressure makes water flow faster. Most household circuits operate on either 115 or 230 volts.

Wires through which the current (electrons) flow are analogous to pipes carrying water. The smaller the pipe, the harder it is to push water through. Similarly, it is harder to push electrons through some wires than others. How hard it is to push electrons through wires is called electrical resistance and is measured in a unit called the ohm. The higher the resistance, the more electron energy that is converted into heat. Copper wire has low resistance which is why it is used in most households. (Can ya tell I had to go through the stages of building a house-- hehehe). Toaster ovens/space heaters employ high-resistance wires so they will produce large amts of heat when current flows through them...

Here's where I always get tangled- the pressure produced by water in a pipe IS the force needed to push it through same. So... Scientists just being redundant there? I usually fall off the learny train about that point, because I live with a scientist and they annoy me, usually with redundancies, and in insisting laws are the same as facts, and are irrefutable- and don't EVEN get me started on how many scientists don't even GRASP the fundamentals of scientific process.... *LOL* About that time she began to quote Kenko and his correlationship from koan to particle physics, and the scientist delivered a blank stare, and wandered off, muttering something about breakfast kooks.