Page 1 of 2 1 2 LastLast
Results 1 to 10 of 20

Thread: Ohms law!

  1. #1
    Jedi Padawan astromech_kuhns's Avatar
    Join Date
    Aug 2008
    Location
    Korriban (sith temple)
    Posts
    637

    Default Ohms law!

    Ok all, there are a bunch that don't know ohms law! Using Wikipedia to learn it doesn't work. I had to read about it and be taught. So i want to make a guide for those who don't know. Now this may be in the wrong section but seemed like the best place to me. Any how here we go......

    Ohms law. It is used to help calculate voltage, current and resistance.

    Lets start with Voltage.

    Voltage which is substituted with a "V" when used in a formula. Voltage is measured in Volts. It is the amount of pressure the battery has. Often used with a water analogy. Voltage is like the pressure in your sink.

    The formula to figure out voltage is V=IxR

    You will learn that later.

    Moving along we have Current.

    Current is substituted with a "I" for formulas. It is measured in Amps. It is how much electricity is moving though the component. (not as vague as electricity but for simplicity's sake we will leave it at that for now.) Often used with the water analogy. Its the amount of water moving through the sink.

    The formula to figure out current is I=V/R

    Also learned later.

    Now to Resistance.

    Resistance is substituted with a "R" for formulas. It is measured in "Ohms". it is the Resistance on the Current. It also is used in the water analogy. It is like the length the pipes have to travel and how small they are, limiting how much can get through. As well as how open the valve is. ex. how open the valve on the handle is. Resistance in electronics can be how small the wire is, resisters (name says it all. it resists current. cause resistance= limiting HOW MUCH can come through and current is HOW MUCH) how long the wire is. the type of material Current is moving through.
    Although not as effecting is the length of the wire. It is not hugely affected much, but it technically does limit some, not anything to worry about though. And if you have to small of a wire it will heat up and stop working in that circuit.

    Recap: Voltage is the pressure, Current is how much and Resistance is limiting how much.


    So if pressure pushes how much and how much is limited that means Voltage moves Current through while Resistance limits Current.

    So now for the formulas.

    V=IxR means that Voltage is equal to Current multiplied by resistance.
    So understanding this now you realize to find one you must have two.

    So let’s pick this apart. Its basic algebra. Replace the variables with the numbers. If you are trying to find Voltage then you need current and resistance values. So let’s say the resistance was 100 ohms. And the current was 0.12 amps. That would be 0.12 x 100 = 12 volts.

    I=V/R means current is equal to voltage divided by Resistance. Again replace the variables. Let’s use the same equation. So as seen before if we have 12 Volts and 1oo ohms then respectively 12/100= 0.12 amps

    R=V/I means resistance is equal to Voltage divided by current. Same equation again means that with 12 volts and 0.12 amps, the formula is 12/0.12 = 100. Hasn’t changed.

    So you can see how a formula works with changing out variables with what you know.

    ex.

    V=IxR
    V=0.12xR
    V=0.12x100
    V=12

    Not to hard is it?

    So how do you have two of these variables and still need another? Well let’s look at it as a problem. If you have a LED with a high voltage of 7 volts and 3 amps, but a battery with 7 volts and 5 amps then you need a resister. A resister resists the amount of current, which is what is too much. So now you need to find out the size of the resister you are using. So if you need 2 amps at 5 volts to be limited from your battery to your LED. so you use the formula R=V/I to find your resister size. so let’s do it!

    R=V/I
    R=5/I
    R=5/2
    R=2.5

    There for you need a resister with 2.5 ohms. That will limit your 2 amps to your LED.

    Now limiting voltage is different. It’s not done the same way. Resistance limits how much remember not the pressure. so what does limit voltage? Nothing really. Voltage is decently something you can have stray from specs. For instance i have a 12 volt battery but a 24 volt motor. It just pulls twice the current. Same as well the LED will only draw so much voltage. But at the same time you can’t overdue it. Now in a project I’m going to do I’m going to use this same 12 volt supply to power some LED's. Small ones mind you. And i will use what is called a voltage regulator for that.

    a voltage regulator steps down the voltage. There is no equation for this. On the package the regulator will say how many amps and volts your power supply will be dropped to. Because that is not affected the way a resister and amps are. it takes the voltage incoming and drops it to what it is set to.

    So if you have too many volts to a component you need then you need to either step down the power supply to a more appropriate voltage or use a regulator. Generally getting a battery with less voltage or using a smaller amount of batteries if you are using many.

    Understanding resistance, current and voltage written.

    Voltage which is volts may also rather than being written like 12 volts may be written like 12V. V standing for Volts.

    Current which is amps may be seen as 0.12A rather than 0.12 Amps.

    a tip to remembering the formula's that i found easy is this, if you can remember the three letters in the equations then its simple. Voltage always likes to be on top. when calculating voltage it is the only one that uses multipilication instead of division. when calculating current and resistance it is division. and voltage will always be on top. only one multiplication when voltage can not be on top.

    Resistance which is ohms may just be seen as simply 100ohms.
    So now you can read it when its written and you know what resistance, current, and ohms law is. You can also now calculate voltage, resistance and current. You are set to go! Now you can calculate your own circuits!

    I may just do a tutorial on components and stuff to….. not sure yet.
    Anyway if any other members want to chime in they can. Any criticism is appreciated! Sure I didn’t do perfectly.
    Last edited by astromech_kuhns; 10-23-2009 at 12:33 PM.
    if you are new these links will get you started

    tutorial on ohms law!!!
    the saber building dictionary-a dictionary with basically everything about sabers!
    thread index-this is the thread index!
    the basic saber building tutorial-tutorial for making basic hilts!
    start here if new-start right here if your brand new fresh out of the factory never before opened noob!


  2. #2

    Default

    Thank you Astromech, that cleared things up for me. I have tried to use that website for ohms law and found it to be a bit confusing. Math was never a strong point for me, so things like that I need to have explained to me. Again, thank you for taking the time to explain it.

  3. #3
    Jedi Padawan astromech_kuhns's Avatar
    Join Date
    Aug 2008
    Location
    Korriban (sith temple)
    Posts
    637

    Default

    Quote Originally Posted by Darth Midian View Post
    Thank you Astromech, that cleared things up for me. I have tried to use that website for ohms law and found it to be a bit confusing. Math was never a strong point for me, so things like that I need to have explained to me. Again, thank you for taking the time to explain it.
    math is not my strong point either to be honest. im still stuck in algebra one thats no good.


    so you are understanding it now? for sure without any doubt? cause even being lade out this can be very confusing. this is a work in progress im sure, as i may have messed up or decide to add more later on. and it is my first tutorial. but do plan to hopefully pop another out today/tomorrow on electrical components. let me know if there is anything your still fuzzy on!
    if you are new these links will get you started

    tutorial on ohms law!!!
    the saber building dictionary-a dictionary with basically everything about sabers!
    thread index-this is the thread index!
    the basic saber building tutorial-tutorial for making basic hilts!
    start here if new-start right here if your brand new fresh out of the factory never before opened noob!


  4. #4

    Default

    I thought I had it. I'm missing something. I already have my switch and resister. I'm using the numbers from them to see if I completley understand. I'm using two trust fires to power my saber, that's 7.4 volts. The led in the switch has a forward voltage of 2.1. The resistor I'm using is a 270 ohm 1/4 watt resistor. (I asked someone.) I don't want to do that everytime I want to add an led to any of my sabers.
    I understood it as dividing 2.1 by 7.4, 2.1 being the V and the 7.4 being the I. The answer I got was 0.2837837. Then I tried subtracting 2.1 from the 7.4 and dividing 5.3 by 7.4 and got 0.7162162. I also tried dividing 2.1 by 5.3 and got 0.3962264. Unless the 0.2837 is the ohms and you round to the closet resister rating to that number? Also, how do you figure out the watts?
    I'm sorry, I thought I had it figured it out. I'm sure it's something simple I'm missing, or I just completley missed the boat. Thank you

  5. #5
    Jedi Padawan astromech_kuhns's Avatar
    Join Date
    Aug 2008
    Location
    Korriban (sith temple)
    Posts
    637

    Default

    well, although your post being a tad confusing, i am seeing a problem already, you used the 7.4 V and substituted it in for I which is current. you said the trustfires have 7.4V and you substituted it for the current in your equation, wich you may have typed something wrong.

    also something i see wrong is you are dividing 2.1 by 7.4 and 5.3 which is your voltages. if you are looking for resistance im guessing? remember, voltage always likes to be on top. so your problem is R=V/I

    so......

    R=V/I
    R=7.4/I
    R=7.4/2.1
    R=3.52

    round that to 3.5, and you need a 3.5 ohmic resister.

    now back to your 7.4 and 5.3, your 7.4 is the voltage you have, and then you subtracted 2.1 which is your amps. look at it this way, if the problem was 7.4V = 2.1A then you cannot simplify that further. you can not mix amps with volts when subtracting or adding like that. they are seperate variables in a sense.

    so to let me help you further could you lay out your components for me with the voltage and amps or resistance depending on the component and then tell me what variable you are trying to find, and i can hopefully help walk you through it.
    if you are new these links will get you started

    tutorial on ohms law!!!
    the saber building dictionary-a dictionary with basically everything about sabers!
    thread index-this is the thread index!
    the basic saber building tutorial-tutorial for making basic hilts!
    start here if new-start right here if your brand new fresh out of the factory never before opened noob!


  6. #6

    Default

    There are led resistor calculators on the web. Better safe than sorry with 30 dollar leds. Get supply voltage. For 2 3.7 Li ions its around 8V. get led fwd voltage. Get current led runs at. Put them in calculator. Do not use smaller res than recommended.

    http://led.linear1.org/1led.wiz

  7. #7

    Default

    Sorry about that. I was using the parts that I have to see if I could figure out ohms law. I'm using two 3.7 V trust fires to power my saber. I purchased the DPDT illuminated switch, it has a forward voltage of 2.1. I was trying to figure out what resistor I needed.
    I already have the resister. It's 270 ohms 1/4 watt. I'm just using these numbers as an example to see how to figure it out. I'm sorry, I really don't mean to be a pain in the rear. I really want to figure this out. I really appreciate the help, thank you.

  8. #8
    Jedi Padawan astromech_kuhns's Avatar
    Join Date
    Aug 2008
    Location
    Korriban (sith temple)
    Posts
    637

    Default

    Quote Originally Posted by Darth Midian View Post
    I'm sorry, I really don't mean to be a pain in the rear. I really want to figure this out. I really appreciate the help, thank you.
    pain in the rear? not at all.

    although the resistor calculators are great they are not good if you are needing to learn this stuff.

    your switch if smaller than the current for the LED would need to come in on the negative side.

    let me know were your problem is and i will help you out best i can! as for the resistor needed if you already have one that you got in a kit then use the equation as best as possible and see if you come up with that you think is correct. and then check it with the resistor color code.
    if you are new these links will get you started

    tutorial on ohms law!!!
    the saber building dictionary-a dictionary with basically everything about sabers!
    thread index-this is the thread index!
    the basic saber building tutorial-tutorial for making basic hilts!
    start here if new-start right here if your brand new fresh out of the factory never before opened noob!


  9. #9

    Talking

    Learning is a good thing but i always double check with other sources. If you let the magic smoke out it won't work anymore.

  10. #10
    Jedi Padawan astromech_kuhns's Avatar
    Join Date
    Aug 2008
    Location
    Korriban (sith temple)
    Posts
    637

    Default

    Quote Originally Posted by Sunrider View Post
    Learning is a good thing but i always double check with other sources. If you let the magic smoke out it won't work anymore.
    thats what that stuff is! lol!

    yeah it is if you do not have the resistor on hand.
    if you are new these links will get you started

    tutorial on ohms law!!!
    the saber building dictionary-a dictionary with basically everything about sabers!
    thread index-this is the thread index!
    the basic saber building tutorial-tutorial for making basic hilts!
    start here if new-start right here if your brand new fresh out of the factory never before opened noob!


Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •