Wiring Question

[stormy87]

For most of the topics on adding LEDs to the armor have been very vague. They say I need a battery holder, LEDs and a resistor. I stopped by Radio Shack and took a look at the supplies and I found that there are many different voltage LEDS and Many different OHM resistors.
1 What kind of resistor do I need?
2 And what voltage LED? I plan on using 2 for this circuit.
3 Most batteries are 1.5 volt and the LED i saw was 1.7 to 2.4 volt. If I get a battery box that takes 2 batteries, does that make 3 volts?
4 How will adding multiple LEDs affect the circuit as a whole? I.E. be dimmer or brighter.
I am sorry for being so noobish, but I have no experience with ohms and volts and watts. I need a crash course.

Link to the LED

 

[Jonny Nny]

It actually goes into pretty deep detail in the wiki....hold on getting link......link acquired

http://halocostuming.wikia.com/wiki/Helmet_LEDs

 

[Carpathia]

To answer your questions...

1. To find out what resistance you need for different source voltages, check out this site. Just enter the source voltage, forward current of the LED's, forward voltage of the LED's and the number of LED's you inted on using. The normal forward current of a 5mm LED is 20mA, which is actually pretty bright.
2. Most LED's have a forward voltage of about 3.2 to 3.5 volts, meaning that when the voltage crosses the LED, they will drop 3.2 to 3.5 volts from the power source. So, two AA batteries (1.5 volts each making 3 volts) will not be sufficient power to light up your two LED's since they require a minimum of 6.4 to 7 volts.
3. I guess that was answered in part 2.
4. The more LED's you put in a series circuit (assuming you don't modify your power source) the dimmer they will light, until the LED's total forward voltage exceeds the provided voltage (power source) at which time the LED's just won't light up. If you design a proper parallel circuit, then they will light at the same brightness, but the battery will not last as long. Luckily, LED's last practically forever and don't put much of a drain on a battery. I have an architectural model I built which I lit with 12 LED's all powered by one 9 volt battery. This was over a year ago, and that battery is still going strong.

If you are looking to use two LED's, I would reccomend using the wiki link the Brothers Darkness mentioned. Use a 9 volt battery for your power source. This is a very simple circuit to put together, so you shouldn't have much trouble once you have your components picked out properly.

I hope this helps you out. I was an electronics technician in the navy for 6 years, so any other questions you have I'd be happy to try to answer. Good luck.

 

[Balthezar]

seems no one has bothered to put the formula up:

V=IR
Voltage = Current X Resistance
(volts) = (amps) X (ohms)

you can figure out your own schematics using this equasion.

subtract the total voltage of your led's from your batery, and then devide that by the current of the system. That will tell you what resistors to use with which lights / bateries.

under-powering will make your lights dim, but over-powering them will burn them out quicker, which is why you use resistors.

 

[Jjack]

just find the LED that can handle higher voltages i run 2 LED in sequence off 1 9volt battery with no resistors but one alone cant handle a 9 volt

 

[stormy87]

Thanks guys, its a big help.

 

[stormy87]

So I went back to RadioShack and found what I think is correct. I used the 2nd schematic on the wiki page, but instead of 3.6V LEDs I bought 1.8V lEDs. So if I am correct I only need 1 9volt battery and a 100 ohm resistor. Is this right?
And another thing that wasn't mentioned was what wattage to get the resistor. There are many different wattage ones, I bought a 1/4 watt resistor. Does this matter?

And I am still confused on the formula.
V=IR
Voltage = Current X Resistance
(volts) = (amps) X (ohms)

Balthezar said to "subtract the total voltage of your led's from your batery, and then devide that by the current of the system"

What is the "current of the system?"

 

[sirblood]

I used automotive LED's. You can get them in several colors and they are VERY bright. they will run off of voltages from 9 to 14v. They are plenty bright enough for me to see in the dark, I used blue which gives a funky glow to whatever you illuminate with them.

Most are made/imported from china, but I bought 6 of them for $20 total (after shipping from hong kong) or so off of ebay.

 

[Balthezar]

instead of 3.6V LEDs I bought 1.8V lEDs. So if I am correct I only need 1 9volt battery and a 100 ohm resistor. Is this right?

Yes, that'll work, but only assuming your 1.8v LED's have the same AMP ratings.

The current of the system is dependant on your LED's. In the second diagram, it says 20 mili-amps MAX, which means your ideal Current is .02A or less. If you hook up 4 LED's the way they have shown (at 1.8v each, assuming the same current draw) your total voltage draw will be 7.2v. The remaining voltage of 1.8v needs to be killed off with the resistor. so 1.8v / .02A is 90 ohms. Remember, this is at the highest amp level. The higher the resister, the lower the amps accross the LED's, allowing them to last a long time while still being bright. 100 ohms is perfect for that setup. If your ideal current is more or less, do the math and plug different numbers. You might need a different resistor.

you can also get more life out of the system by using both bateries, but hooking them up in parallell instead. Hope it makes sence now...

Watts are a measure of power, which is calculated from Voltage and Amp-hours. So basically its the inverse of resistance, but given in "how many hours your batery will run this".

 

[Kaya Tetsu]

There are plenty of topics on this floating around. I really don't think any of them cover the formulas and such though. This is one of the few physics topics that was easy. I'll write something up later. I'm running late for class.

 

[stormy87]

Yes, that'll work, but only assuming your 1.8v LED's have the same AMP ratings.

The current of the system is dependant on your LED's. In the second diagram, it says 20 mili-amps MAX, which means your ideal Current is .02A or less. If you hook up 4 LED's the way they have shown (at 1.8v each, assuming the same current draw) your total voltage draw will be 7.2v. The remaining voltage of 1.8v needs to be killed off with the resistor. so 1.8v / .02A is 90 ohms. Remember, this is at the highest amp level. The higher the resister, the lower the amps accross the LED's, allowing them to last a long time while still being bright. 100 ohms is perfect for that setup. If your ideal current is more or less, do the math and plug different numbers. You might need a different resistor.

you can also get more life out of the system by using both bateries, but hooking them up in parallell instead. Hope it makes sence now...

Watts are a measure of power, which is calculated from Voltage and Amp-hours. So basically its the inverse of resistance, but given in "how many hours your batery will run this".

How do I know how many Amps my system has?

 

[thatdecade]

The amps are determined by your resistor selection. Just make sure that your battery is not larger then double the voltage the LED is rated for. Then use the v=ir equation to figure out the correct resistance to use. The rated current (amps) of the LED is printed on the packaging.

Example:
LED is rated as 2.3V & 20mA
You want to run it with a 3V battery pack.
3/.02=150 ohm
In this situation you need a 150 ohm resister.


Not that any of this matters, it's just an LED so you just have to be close with the ratings. When it says 20mA MAX, that is the rated current. At the rated current it will have the rated life span of ~100,000 hours (11 years).
If you connect things wrong and end up running it at 50mA instead, your runtime will be less, say ~60,000 hours (7 years).

 

[Balthezar]

There are plenty of topics on this floating around. I really don't think any of them cover the formulas and such though. This is one of the few physics topics that was easy. I'll write something up later. I'm running late for class.

I agree. there needs to be a sticky on the subject. maybe even with a short sections on fans, and entire-suit wiring. Joint effort?

 

[stormy87]

I agree. there needs to be a sticky on the subject. maybe even with a short sections on fans, and entire-suit wiring. Joint effort?

Or maybe web page where you plug in your LEDs and their voltage and it maths it out for you. That would be sweet.

Where do you guys get your electrical parts like switches and LEDs? I got pwnt by RadioShacks prices.

 

[Kaya Tetsu]

I agree. there needs to be a sticky on the subject. maybe even with a short sections on fans, and entire-suit wiring. Joint effort?

Sure, Joint efforts are always better.

Or maybe web page where you plug in your LEDs and their voltage and it maths it out for you. That would be sweet.

Where do you guys get your electrical parts like switches and LEDs? I got pwnt by RadioShacks prices.

There are a few of those floating around. Google should come up with some results. Also there s this magical thing called the internets. No, actually look around for some small shops in your area or recycle stuff. Try to find stuff people are going to throw away and take it apart and save things that still work that you can use then recycle the rest properly. The internet can be a good place for stuff (compared to radio shack),but shipping will kill you sometimes (even for light things) and a lot of places online with good prices require you to buy in bulk.

 

[stormy87]

I found a link on the interweb that calculates everything. Here ya go
LINK