3.2v LEDs 12v battery

[Orion96]

I know this is a very basic concept but I can't rap my head around this one. I've got nine 3.2v blue LEDs rated for 20mA and I want to run them off of a 12v 7Ah battery. What I've done is I've put 3 LEDs in parallel then another 3 and another 3 so that's 3 sets put into series but that would make it 4 volts each (am I right?) so I put one extra LED in the series line to make the voltage 3 volts (I don't have the right resistors) my question is, is this the most effective way to wire it up for brightness, I'll get a resistor some day. And what would be the best way to wire it up? Also what would the power consumption be with how I've set it up?

Thanks in advance for your help.

 

[Colin Mitchell]

You must get a resistor before we can even talk to you.

 

[Orion96]

You must get a resistor before we can even talk to you.

What resistor should I get

 

[Martaine2005]

https://www.electronicspoint.com/threads/got-a-question-about-driving-leds.256849/
Have a read of that. It will help you understand LEDs.
If you find something you don't understand, you can ask here.

Martin

 

[BobK]

You have the right idea with series and parallel, but you have it backwards.

What you need is 3 strings of 3 in series with a resistor in each string. Then you parallel those three strings.

The resistor has to drop 12 - (3 * 3.2) = 2.4V at 20mA of current. Use Ohms law to calculate the resistor.

Bob

 

[Colin Mitchell]

Buy
3 x brown-grey-brown-gold and
3 x brown-red-brown-gold

 

[BobK]

Yes, buying those resistors will make it work, even if you do not use them in the circuit.

 

[Orion96]

https://www.electronicspoint.com/threads/got-a-question-about-driving-leds.256849/
Have a read of that. It will help you understand LEDs.
If you find something you don't understand, you can ask here.

Martin

Thanks for the link. I haven't read all of it yet, but I find it very interesting.

 

[Martaine2005]

Yes, It's a good read.
I thought it would be easier to read that first, and then ask questions later if needed..
But it's easy to understand.

Martin

 

[Orion96]

You have the right idea with series and parallel, but you have it backwards.

What you need is 3 strings of 3 in series with a resistor in each string. Then you parallel those three strings.

The resistor has to drop 12 - (3 * 3.2) = 2.4V at 20mA of current. Use Ohms law to calculate the resistor.

Bob

Thanks for the help I'll do it that way, only problem is getting the resistors South Africa is a bit useless when trying to buy parts like that.

 

[BobK]

Do the Chinese suppliers on Ebay ship there? They are a good source for parts like resistors, but it can take weeks for shipping.

Bob

 

[Martaine2005]

Do the Chinese suppliers on Ebay ship there? They are a good source for parts like resistors, but it can take weeks for shipping.

Bob

I think the problem is with the postal system there. They "seem" to "lose" things very easily!!
Or at least the head honcho's think "finders keepers".....

Martin

 

[BobK]

I think the problem is with the postal system there. They "seem" to "lose" things very easily!!
Or at least the head honcho's think "finders keepers".....
Martin

If they are stealing resistors, they must be quite desperate!

Bob

 

[Martaine2005]

They steal the sellotape the envelope is sealed with too!!
Corruption is awful in that country.

 

[Orion96]

W

Buy
3 x brown-grey-brown-gold and
3 x brown-red-brown-gold[/QUOT]
Why two lots of resistors won't the 120 be alright?

Do the Chinese suppliers on Ebay ship there? They are a good source for parts like resistors, but it can take weeks for shipping.

Bob

They do, I bought the LEDs from Banggood to see if they are any good, prices are really good but I waited over a month for it.

 

[Martaine2005]

They do, I bought the LEDs

Perhaps the head honcho has enough LEDs Or you was just lucky?

Martin

 

[Orion96]

I

They steal the sellotape the envelope is sealed with too!!
Corruption is awful in that country.

It is very bad, the postage system was nearly shutdown, all the money is being stolen

 

[Orion96]

Perhaps the head honcho has enough LEDs Or you was just lucky?

Martin

Does the world know how full of sh*t SA
is? Where you from?

 

[Martaine2005]

Anyway, getting back to your original question, you said you don't have the right resistors?
You can series and/or parallel them to get what you need!

Martin

 

[Martaine2005]

Does the world know how full of sh*t SA
is? Where you from?

Erm, yes...
I can see your flag. Can you not see mine?