LED question - The Planted Tank Forum
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 18 (permalink) Old 01-02-2012, 08:38 PM Thread Starter
Planted Tank Guru
 
scapegoat's Avatar
 
PTrader: (16/100%)
Join Date: Jun 2010
Location: philadelphia, pa
Posts: 2,454
LED question

I purchased a cheap battery powered LED "strip". it's basically just a wired strand of 30 blue LEDs powered by 3 C batteries (4.5v total) and has a small resistor that I believe is gold black black brown. which, according to http://www.dannyg.com/examples/res2/resistor.htm, is a 10 ohms +/-5% resistor...

now... this thing has 30 leds and is about 10' long, i want to wire up three or four of these into my t5ho unit... ultimately powered by a single, smaller battery... AA or AAA to hide within the light unit and toggled on with a push button.

I've got no problem wiring things up... my problem is figuring out the power aspect... how much power do i need for 3 or 4 LEDs, and do i need a resistor?

this is pretty much what i've got, only more LEDs

http://www.amazon.com/Battery-Operat...ref=pd_sim_k_3
scapegoat is offline  
Sponsored Links
Advertisement
 
post #2 of 18 (permalink) Old 01-03-2012, 12:01 AM
Planted Tank Guru
 
PTrader: (84/100%)
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 21,012
You need to know how the LEDs are connected - series, parallel, or both - and what the forward voltage is for one LED. Then you can determine how to connect them up to run on a battery. Usually no resistor is needed, since the battery voltage drops as the current goes up, so that limits the current well enough. But, if those are very low current limited LEDs, you would need a resistor.

Hoppy
Hoppy is offline  
post #3 of 18 (permalink) Old 01-03-2012, 01:09 PM Thread Starter
Planted Tank Guru
 
scapegoat's Avatar
 
PTrader: (16/100%)
Join Date: Jun 2010
Location: philadelphia, pa
Posts: 2,454
Quote:
Originally Posted by Hoppy View Post
You need to know how the LEDs are connected - series, parallel, or both - and what the forward voltage is for one LED. Then you can determine how to connect them up to run on a battery. Usually no resistor is needed, since the battery voltage drops as the current goes up, so that limits the current well enough. But, if those are very low current limited LEDs, you would need a resistor.
i'm thinking parallel, there is one wire in and one wire out from battery box. so positive to positive to positive, etc on the leds. I don't know how to get the forward voltage though
scapegoat is offline  
 
post #4 of 18 (permalink) Old 01-03-2012, 06:53 PM
Planted Tank Guru
 
PTrader: (84/100%)
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 21,012
If you run 3 or 4 of these in parallel you will need a D cell, at least. That adds up to a lot of current for a battery to supply. I doubt that an AA battery could drive a single string for more than a few minutes, if that. You could experiment until you find a good combination with an acceptable lifetime.

Hoppy
Hoppy is offline  
post #5 of 18 (permalink) Old 01-03-2012, 06:57 PM Thread Starter
Planted Tank Guru
 
scapegoat's Avatar
 
PTrader: (16/100%)
Join Date: Jun 2010
Location: philadelphia, pa
Posts: 2,454
Quote:
Originally Posted by Hoppy View Post
If you run 3 or 4 of these in parallel you will need a D cell, at least. That adds up to a lot of current for a battery to supply. I doubt that an AA battery could drive a single string for more than a few minutes, if that. You could experiment until you find a good combination with an acceptable lifetime.
maybe we're confusing each other now lol

I only want to run 3 or 4 LEDs, 30 are being ran off of three C's right now.

i'm confused about batteries too, since i'm reading aaa's are 1.5v each... and C's are rated at that as well. I assume its the capacity that changes in size? so i could run three AAA batteries on this 30 strand, but they'll lose charge much quicker.
scapegoat is offline  
post #6 of 18 (permalink) Old 01-03-2012, 07:00 PM
Planted Tank Enthusiast
 
Naekuh's Avatar
 
PTrader: (1/100%)
Join Date: Oct 2011
Location: Los Angeles
Posts: 884
i hope your not intending to grow anything off these led's....

also i hope its just for added lighting effects.. because ur not going to get any growth on those leds.
Naekuh is offline  
post #7 of 18 (permalink) Old 01-03-2012, 07:12 PM Thread Starter
Planted Tank Guru
 
scapegoat's Avatar
 
PTrader: (16/100%)
Join Date: Jun 2010
Location: philadelphia, pa
Posts: 2,454
Quote:
Originally Posted by Naekuh View Post
i hope your not intending to grow anything off these led's....

also i hope its just for added lighting effects.. because ur not going to get any growth on those leds.
my initially reaction is to respond with a post dripping of sarcasm. However, no, these will be used for moonlights. I have a t5ho fixture for the plant growth, along with dosing ferts and pressurized co2.

I figured this would be a nice easy project that could be hidden within the t5ho housing.
scapegoat is offline  
post #8 of 18 (permalink) Old 01-03-2012, 08:23 PM
Planted Tank Guru
 
GraphicGr8s's Avatar
 
PTrader: (10/100%)
Join Date: Apr 2011
Location: West coast of the east coast of the USA.
Posts: 4,327
Quote:
Originally Posted by scapegoat View Post
i'm thinking parallel, there is one wire in and one wire out from battery box. so positive to positive to positive, etc on the leds. I don't know how to get the forward voltage though
Just because there are only 2 wires you can't tell if it's parallel or series. Both will have just 2 wires from the battery box.

Here's a decent calculator for the resistors and it will design arrays for you for multiple leds.

http://led.linear1.org/1led.wiz
GraphicGr8s is offline  
post #9 of 18 (permalink) Old 01-03-2012, 09:27 PM
Planted Tank Enthusiast
 
Naekuh's Avatar
 
PTrader: (1/100%)
Join Date: Oct 2011
Location: Los Angeles
Posts: 884
Quote:
Originally Posted by scapegoat View Post
my initially reaction is to respond with a post dripping of sarcasm.
lolol...

yeah moon light is lighting effect, and it should look nice....



Also if a 1.5V battery can power the array, it has to be in parallel..
I cant think of any LED's which u could string up like that in serial and have it run 1.5V.
LED's of low wattage class typically have a power req of 1.5V-3V. Automotive LED's like the ground effect strips done in serial and require 12V.

So im going with paralell wiring on the LED's if a 1.5V battery can provide it with enough current.
Naekuh is offline  
post #10 of 18 (permalink) Old 01-04-2012, 02:19 AM
Wannabe Guru
 
PTrader: (0/0%)
Join Date: Aug 2010
Location: Wake Forest NC
Posts: 1,121
I wouldn't bother trying to run these off of batteries.

I would run them off of a small DC power supply. You probably could use a 5 volt cell phone charger to drive them if you need 4.5v. The 5.0v shouldn't be a problem, and I doubt they'd take more current that the phone charger can output.


You can use automotive LEDs on any common 12v wall charger. I've done it. They make great moonlights but you may have to use a lower voltage--- I used a 9v with the moonlights I used to have and the brightness was dead-nuts perfect.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
redfishsc is offline  
post #11 of 18 (permalink) Old 01-04-2012, 08:10 PM
Planted Tank Enthusiast
 
Naekuh's Avatar
 
PTrader: (1/100%)
Join Date: Oct 2011
Location: Los Angeles
Posts: 884
wait also its 1 battery? or 2 batteries?

2 batteries in series = 3V
Naekuh is offline  
post #12 of 18 (permalink) Old 01-04-2012, 10:14 PM Thread Starter
Planted Tank Guru
 
scapegoat's Avatar
 
PTrader: (16/100%)
Join Date: Jun 2010
Location: philadelphia, pa
Posts: 2,454
I may have made my original post more confusing than it needs to be. I have a 30 led strand powered by 3 C batteries in series(4.5v) w/ an unknown resistor.

I want to remove 3 or 4 of the leds from the strand and wire them into my t5ho hood and power them from a single, smaller, battery.
scapegoat is offline  
post #13 of 18 (permalink) Old 01-04-2012, 10:56 PM
Planted Tank Enthusiast
 
Naekuh's Avatar
 
PTrader: (1/100%)
Join Date: Oct 2011
Location: Los Angeles
Posts: 884
is there a resister after each series?

id say its probably safe to cut b4 after each resistor... however ur still going to need a 4.5V feeding current to it..
Naekuh is offline  
post #14 of 18 (permalink) Old 01-05-2012, 01:56 AM Thread Starter
Planted Tank Guru
 
scapegoat's Avatar
 
PTrader: (16/100%)
Join Date: Jun 2010
Location: philadelphia, pa
Posts: 2,454
nope, there is a single resister

so it's three C batteries, switch, resistor. negative and positive out to first led, then a neg and positive from that led to the next, and so on until the last led where the wiring stops.

the batteries are reverse order, as one usually see's... so

- + ----------------------\ /--------\
+ -.................................={led}.....={led} (+28 more LEDs)
- + ---[switch]--[resistor]-/ \--------/

judging by the fact that there are 30 LEDs being ran by 4.5v (- whatever from the resistor) I think a single 1.5v battery would be appropriate for ~10 LEDs... so i would need a resistor, or a few, to run 3 or 4 LEDs off of a single 1.5v, correct?
scapegoat is offline  
post #15 of 18 (permalink) Old 01-05-2012, 02:11 AM
Planted Tank Guru
 
PTrader: (84/100%)
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 21,012
Wow, this really got complicated. Your original 30 LED chain needs 4.5 volts to operate. Assuming they are wired in parallel, which they seem to have to be, you would need 1/10 the voltage to power 3 LEDs, or 1/2 volt, roughly. So, you would need a resistor to drop a 1.5 volt battery voltage down to .5 volts. Assume the current needed is ??. The resistor needs to be 1/?? ohms. This isn't critical because an AA battery voltage would droop considerably with the amount of current you need. Unfortunately I don't know how much current those LEDs need. I think I would look for a trim pot to put in the circuit and use it as a rheostat to adjust the current up from zero to where the LEDs light up.

EDIT: I'm confused! You need 1/10 the current to power 3 LEDs, not voltage. But, you still need the same voltage, or 4.5 volts. So, you need to determine the forward voltage drop across one LED, and the desired current in order to figure out what size resistor is needed. But, it used a 10 ohm resistor for 30X one LED's current, to drop the voltage down to equal the forward voltage drop. So, perhaps (?) you need 100 ohm to get the same voltage drop when using only 3 LEDs (1/10 the current)

Hoppy

Last edited by Hoppy; 01-05-2012 at 04:38 PM.
Hoppy is offline  
Reply

Tags
None

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the The Planted Tank Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome