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series / parallel ? for you electronic experts

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axkiker

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Discussion starter · #1 ·
Well as I am finding out I have pretty much forgotten all the electrical theory I had in school. the only thing I remember is dont touch the hot wire...

Im working on an led project and have a question about which way to wire them up. I have 5 leds and have decided to wire them up one of 2 ways. One is a series / parallel combination. the other is all of them parallel.

the series paralles combination will provide the least amount of draw on the battery and of course the parallel version is the most. The parallel version would be easier to wire.

Is the brightness going to be effected based on which way I wire them. Either way they will get the voltage they need but it just seems to me that the parallel way would be brighter since its drawing more from the battery.

any ideas.....
 
#4 ·
I'd go parallel, and be careful with series/parallel circuits when using matched components. Voltage drops are additive through any given loop back to the source (battery) so two LEDs wired in series will each be half as bright as the LED wired parallel to the battery.

If you must do a combination ckt than you'll need to order your two series LEDs with 1/2 the resistance to match the one LED parallel to them. :winker:
 
#5 ·
Cheap Christmas lights are in series because it is cheaper to make.

Ever tried to figure out which light was out?

PARALLEL is the only way to go when it comes to lights for Christmas or boat trailer lights.

JMHO
 
Discussion starter · #7 ·
Ok so here is my delima.

In the ed calculator it says that I can run all these leds in parallel with 15 ohm resistors. The problem is that the resistors need to be capable of roughly 7 watts. Well thats one heck of a resistor and there is no way I can fit 5 of them in this case.

So now im thinking that the best may be to limit down the voltage to the 3.5 needed and then run them all in parallel.

My issue is that I cant remember what happens to the wattage when running them in parallel. does it go up for each diode or since they are in parallel does the wattage remain consistant...

i forget.....
 
Discussion starter · #9 ·
Fyhr Factor said:
Something just does'nt sound right, What are the spec's on the Leds your using and how many do you plan to use in the housing..




Because I seem to come up with 1/2watt resistors..
Click to expand...

each led run at 700mW these are those little star deals. 3W a piece.

I hooked just one of them up with a 1/2W resistor and almost burnt my finger after just a few seconds.
 
Discussion starter · #10 ·
Okay so I looked up some school books and did a little refresher. see if this makes sence

Ill have 5 leds with a forward voltage of 3.5V at 700mW each

I plan on wiriing them in parallel

So insted of attaching a resistor on each led I thought it would be better to pull the input voltage down with one main resistor and then just wire each led straight up.

So 5 these 5 leds in parallel would need an input voltage of 3.5V and require a resistor that is 41 ohms and capable of 3.5W

does thissound about right??????

wow its been a while since I did any of this
 
#12 · (Edited)
axkiker said:
each led run at 700mW these are those little star deals. 3W a piece.

I hooked just one of them up with a 1/2W resistor and almost burnt my finger after just a few seconds.
Click to expand...
OOPS, Sorry.. :(

Hey, what do I know, I only wire houses , not electronics :laugher:

I did'nt know your spec's, so I used some standard Led specs..

When I used their Calculator, It came up with a 1/2 W (580 ohms) resistor on each Led using 5 Leds..in a parallel circuit.

I might actually have to put on my thinking cap on for this one.. I'll see what I can come up with, if anything..

Here's some info..
http://www.theledlight.com/LED101.html
 
Discussion starter · #13 ·
Fyhr Factor said:
OOPS, Sorry.. :(

Hey, what do I know, I only wire houses , not electronics :laugher:

I did'nt know your spec's, so I used some standard Led specs..

When I used their Calculator, It came up with a 1/2 W (580 ohms) resistor on each Led using 5 Leds..in a parallel circuit.

I might actually have to put on my thinking cap on for this one.. I'll see what I can come up with, if anything..

Here's some info..
http://www.theledlight.com/LED101.html
Click to expand...

I feel horrible. I spent THOUSANDS on schooling now I cant even calculate out a parallel circuit. HAHAHA Good lord imagine if this were a series and parallel circuit. I would be screwed..
 
#14 ·
Here's another calculator..
http://ledcalc.com/#calc

I can figure it out, as long as the spec's are correct, But,,,,, what has me confused are the spec's for the LED's your using..
OK, you have 3 watt Blue Led's rated for 3.5 V , that I get..

But I'm Not sure what the milliamps rating is for it,
you gave me spec of 700 mW , but what's the spec's in mA ???

or was that a typo ??
 
#15 ·
axkiker said:
I feel horrible. I spent THOUSANDS on schooling now I cant even calculate out a parallel circuit. HAHAHA Good lord imagine if this were a series and parallel circuit. I would be screwed..
Click to expand...
HA I have a freakn degree in this field and have forgotten probably 90% of the stuff i learned! Thats what happens when you are out of your intended field for some 10+years now! :(
Lets see if can remember any of this.....
What i do remember is total current in a parallel circuit is the sum of all the current drops on that circuit....so if each LED is a true 3W draw and you have dropped the voltage suply to each LED via resistor to the 3.5V then each LED will draw .857 amps .....so take the amps (.857) and multiply it by 5 (for 5 LED's) you get 4.28 total amps.....
Now what ever voltage drop circuit you build will need to handle that amp load.....4.5 amps doesnt sound like alot but for a small resistor you will probably need a small heat sink of some sort to keep it from burning up...
 
Discussion starter · #16 ·
Fyhr Factor said:
Here's another calculator..
http://ledcalc.com/#calc

I can figure it out, as long as the spec's are correct, But,,,,, what has me confused are the spec's for the LED's your using..
OK, you have 3 watt Blue Led's rated for 3.5 V , that I get..

But I'm Not sure what the milliamps rating is for it,
you gave me spec of 700 mW , but what's the spec's in mA ???

or was that a typo ??
Click to expand...
Well im no expert on this stuff but I think the 3W has something to do with the output and the 700mW is the wattage that the unit draws... Im not totally sure but I know you use the 700mW when calculating the resistors needed. Im not sure why they dont list them in Amps. That makes no sence to me...
 
Discussion starter · #17 ·
Wally said:
HA I have a freakn degree in this field and have forgotten probably 90% of the stuff i learned! Thats what happens when you are out of your intended field for some 10+years now! :(
Lets see if can remember any of this.....
What i do remember is total current in a parallel circuit is the sum of all the current drops on that circuit....so if each LED is a true 3W draw and you have dropped the voltage suply to each LED via resistor to the 3.5V then each LED will draw .857 amps .....so take the amps (.857) and multiply it by 5 (for 5 LED's) you get 4.28 total amps.....
Now what ever voltage drop circuit you build will need to handle that amp load.....4.5 amps doesnt sound like alot but for a small resistor you will probably need a small heat sink of some sort to keep it from burning up...
Click to expand...

I think you and I are almost on the same page however you are using the 3W to calculate the inpedance needed verses the wattage used (700mW)

From my understanding when they list this particular type the rate the output in watts (3W) but the actual wattage draw is 700mW.

Im not at all sure this is all new to me. .... Rerun your numbers using the 700mW and see if we are on the same page...
 
#19 ·
Impedence is usually only accociated with AC ciruits....what i was doing is using Ohms law to find out the current...you had the wattage=P (3W) and the voltage=V being used (3.5V) so P/V=I(current) 3/3.5=.857A x 5 LED's = 4.28A thats how i came up with it in the begining....but yes i see how it can be rated as a 3W LED in brightness alone...not actuall Wattage...
 
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axkiker
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