LED light unit

[Oxfordelectro]

Hi,

I am very new to electronics so please bare with me. I'm currently working on an LED light unit for plant growth. Each unit has 5 separate units running in parallel off a 35-55v power supply, each one of the five unit has 18 LED wired in series, each LED is 3watts and Various voltages depending on colour (I assume). Some of the LEDs on these units have blown due to water ingress and as they are wired in series the whole unit doesn't work. I have identified the faulty LEDs and replaced them for the correct colour, but for some reason on on the units I have changed the LEDs on the particular unit of a lot brighter than the rest, even the original LEDs have become much brighter.

Any ideas of why this is?

Apologies of this makes no sense and not in the correct catagory.

 

[dknguyen]

I would think it was because the LEDs you used to replace the old ones were from a different manufacturer batch (or maybe altogether entirely different manufacturer?) and had a slightly lower voltage drop which causes more current to flow through the entire chain than before.

 

[Oxfordelectro]

I would think it was because the LEDs you used to replace the old ones were from a different manufacturer batch (or maybe altogether entirely different manufacturer?) and had a slightly lower voltage drop which causes more current to flow through the entire chain than before.

Thank you for the reply.

Yes, basically they are cheap Chinese light units and I can't source the "actual" parts. So I would need to find some Leads with a higher forward voltage?

 

[dknguyen]

Yeah. Or you can increase the value of the series resistor to compensate. Measuring the voltage directly across an old LED while they are on should tell you what the forward voltage drop needs to be. You can measure the voltage drop across the old LED will tell you how far it is off by.