Help with resistors - DIY LED

[Nicmar]

I am building the following and need to know what size resistor to use eg 1oh 5w. I have conflicting info some saying it is not important and others saying it is.

Driver 1 - ELN-60-48D
12 CREE XP-E BLUE led
I don't think I need it for this one, just a fuse.

Driver 2 - ELN-6048D
12 x 2 in parallel (24 total)
CREE XT-E Royal Blue

Driver 3 - ELN-60-48D
Cool White XP-G 12 and 12 Neutral White XP-G 5W in parallel
12 x 2 (24 total)

 

[byee]

From my understanding current limiting resistor is not required with the drivers.

May want to also ask the customer service/support team at Meanwell to confirm. Replies from them are very quick.

 

[sleepydoc]

LED drivers are typically constant current, not constant voltage. They typically have a minimum and maximum voltage they can supply, but within that voltage range the current stays constant.

Adding a 'current limiting resistor' with a constant current power supply will accomplish nothing unless the power supply is already at it's peak power. The only place where it would make sense is if you are using fewer LEDs than the driver was meant for and need to step down the voltage for a given current.

 

[RocketEngineer]

The resistor is only needed in parallel strings and is NOT for current limiting. The 1ohm resistor allows you to measure current in each string without having to put the multimeter inline with each string. Instead you measure the voltage drop across the measurement resistor and using V=IR where R=1 you get I (current) directly. Easy, simple, no connecting/disconnecting required. This can work for a single string but it's only necessary for parallel so you can balance the strings.

Oh, and it wouldn't hurt to include a fuse in each parallel string so if something goes in one string the other one doesn't get fried as well.

 

[insomniac2k2]

Like RocketEngineer said. Resistor for measurement (balancing your strings). Fuse is necessary IMO. You do not want to blow out a whole string because you cheaped out on a dollar fuse

 

[Nicmar]

@RocketEngineer you understand what I am doing.
I want to use it to balance the strings.
I am just not sure what size to use or does it not matter?

 

[RocketEngineer]

1 Ohm 5Watt is the typical size. I got mine online but you may have to search around for them. The physical dimensions aren't important, just the rated wattage.

 

[insomniac2k2]

Frys has them, but they are a bit big. I used them in my parallel build.

 

[Gorgok]

You can also use a smaller 0.1 ohm resistor, but the value you measure will not be 1:1 anymore (its shifted by a decimal point)... But 0.07 volts instead of 0.7 volts is pretty easy to read still =D. I have sets of those for each channel on my own drivers.

 

[Nicmar]

I have finally wired all my lights up.
The only parallel string using Cree royal blue LEDs isn't working.
When I turn the power on nothing happens, then when I turn it off the turn on for a second then off.
I'm guessing the driver doesn't have enough power to power it.
I have read other people using the same setup though so not sure why it doesn't go.
Does the 5watt 1 ohm resistor play a part in it or do I need to drop from 12 LEDs per string to 11.

 

[Nicmar]

Lol I didn't have the 10v dimmer plugged in!