Help me understand LED diode milliamp ratings

skimjim

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For those following my retro project....

My Driver/Power Supply says on the sticker it provides 550mA continuous power at a dimmable voltage of 60-100v

My 3watt 3.5ish volt LED diodes VARY in milliAmp ratings:
* one batch is 700mA
* a 2nd one 500mA
* a 3rd batch 350mA

What is to be expected when they are all inline running off the power supply?
 
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GabeM

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It has been a while since I've done LEDs but I believe you will see a current through all of the devices at 550mA, overdriving some and underdriving the others. You may be able to lower the 550mA with the dimmer.
 

beaslbob

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Under the assumption that all leds are wired in parallel and have the same voltage, the currents to each add up. But that is a general electrical theory but I don't know about the specific LED behavior.
 

redfishbluefish

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Hey Skim, I'm just a dumb chemist and what I know about amps is what @beaslbob posted above....amps in parallel are additive. My electronics guru has moved out of State, but have to believe we have folks here who can comment. Let me go back through some old posts and see if I can identify some of these folks.

Possible experts:
@Ranjib .
 

Joekovar

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LED marketing is as sketchy as harddisk marketing was years ago.

There's sellers advertising the max pulsed voltage/current which leads the average person to believe they can source that much constantly, when reality they're only designed to operate at that rating for milliseconds at a time.

Another marketing ploy is to sell packs of 10 and list them as 350ma, but not specify that 350ma is the draw of the whole pack, not each individual LED.

The best thing to do is find LEDs with datasheets available. Here's an example of a datasheet that provides a decent amount of information.

An important bit of information you'll find in datasheets, is test conditions. How much power was actually used to get that xxx nm wavelength it's designed to emit? A lot of times the advertised wavelength wasn't generated at the maximum operating specs, and running at specs different than the test conditions is going to give you wavelength closer to the outlying edges of the advertised spectrum.

There's more to it, for instance operating temperatures, but hopefully this is enough to spark some thought on it.
 

Lingwendil

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+1, except the good stuff isn't sketchy at all :)

With all things electronic, first read the datasheet. If no datasheet is available, buy different components from a reputable supplier that provides them. ALL of the big name LED manufacturing houses provide quality data to go off of, such as LumiLEDs, Bridgelux, Cree, SemiLED, Seoul, etc. The no-name stuff off of ebay, alixpress, etc- not so much. Stick to the milliamp rating provided for them, and err on the lower side.


A more direct answer-
Your driver can handle 550mA continuous, so if all of you LEDs are driven in series off of this driver they will all see 550mA. Do not drive them in parallel due to the differences in forward voltages causing unequal current sharing. If the 300mA ones will not take 550mA, run them on a different driver.
 
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hubcap

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If Im not mistaken, different "colored" LEDs have different forward voltages.
If you don't know the forward voltage (Vf) and a data sheet isn't available I (think I) know of two ways to determine Vf
1. use a "Fluke" meter set to the diode setting. If the diode lights, it displays the Vf (its been a while)
2. Hook LED up to a DC source, starting at 0V output and gently up the voltage until it lights. That voltage is the Vf.


Oh, and always have OHMS LAW on standby.
Voltage=Current x Resistance
Helps tremendously, in many electrical situations, if you know the value of two of the three variables.

this link might help with OPs question....

Chime in if Im off-base folks....
 
OP
skimjim

skimjim

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OP here

Back to my original question now reworded a different way

If my driver is forwarding 550mA.... when it gets to my 420nm that's rated at 350mA is that diode being "overdriven" and likely to burn out quickly?

I looked at some data on all my diodes:
* 420nm - 350mA - 5v forwarding
* 440nm - 500mA - 5v forwarding
* 460nm - 700mA - 5v forwarding

I'm just concerned with the 420nm 350mA getting too much current.

I know enough about circuitry to be ignorant & knowledgable
 

oreo5457

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OP here

Back to my original question now reworded a different way

If my driver is forwarding 550mA.... when it gets to my 420nm that's rated at 350mA is that diode being "overdriven" and likely to burn out quickly?

I looked at some data on all my diodes:
* 420nm - 350mA - 5v forwarding
* 440nm - 500mA - 5v forwarding
* 460nm - 700mA - 5v forwarding

I'm just concerned with the 420nm 350mA getting too much current.

I know enough about circuitry to be ignorant & knowledgable
All a bit confusing .

First thing that you didn't ask is all diodes in series @ 550mA need to have an added voltage of at least 60V but no more than 100V
In other words if a particular diode meters 3.6V when supplied w 550mA of current you need at least 17 diodes in series but no more than 27....
Diodes of different V(f)'s aren't an issue.. just add them up as in the above example..

too few (added voltages below 60) and the driver will likely go into limp mode.
Too many and your current won't be regulated.
At least in general.... Point is you need to keep in the range.

Now back to your first problem.. yea you could have issues w/ running 350mA "class" (1W class) diodes at 550mA.
W/ proper heat sinking/fans and good mounting tehnique you "may" get away w/ it but w/ most cheap diodes really listing more of the max current (or at least its a safe assumption) than an average current I'd bet against it.


what's confusing here is is this recommended current? Max current? Average current recommendations?
Typical current voltage relationship..
Shows these things are sliding scales not engraved in stone numbers.



 

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