I am looking to replace a couple burnt out uv diodes on my xr30 g3 pro. I know ecotech uses 2.5w semiled's for uv but all I can find online are 3w semiled's. Anyone know if it will still work and be ok to use the 3w's instead of the 2.5w's?
Radion xr30 replacement uv diode
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DanyL
Valuable Member
You might be right, and I don’t know how the LEDs are configured on the Radion - but if resistance is different it could affect other LEDs connected in series.
You can probably use the three watt LEDs because no doubt they have constant current drivers and resistors in the path. Going the other direction wouldn't work.
No.
Only thing resistance really matters for is to determine the voltage across the led at the set current.
As an led heats its resistance drops and thus it will take less volts to draw same current.
LED internal resistance is not static.
Thermal runaway is the led heats enough at the voltage to cause a large increase in the current draw and then burning out. That is why one needs to "control" the current.
Anyways here is the relation between current and voltage. Use it to calculate watts.
At 3.5V across it it will pull 300mA or approx 1W for example.
When one uses a step down driver at 300mA it will regulate the voltage. In the above example it will "allow" 3.5V across the led (note though at 25C).Therefore maintaining the current at 300mA. When the led warms the current drain may be say 350mA @ 3.5V. The driver will regulate the voltage down to like 3V in order to keep the current output at 300mA
My understanding of it.
Last edited:
Err, ok. Regardless, not an issue.
DanyL
Valuable Member
I’m actually speaking from experience with a really old (first gen?) Maxpect Razor fixture that had this problem - basically making other LEDs in the chain loose some power due to what I thought was a change in resistance of one of the LEDs in the array.No.
Only thing resistance really matters for is to determine the voltage across the led at the set current.
As an led heats its resistance drops and thus it will take less volts to draw same current.
LED internal resistance is not static.
Thermal runaway is the led heats enough at the voltage to cause a large increase in the current draw and then burning out. That is why one needs to "control" the current.
Anyways here is the relation between current and voltage. Use it to calculate watts.
At 3.5V across it it will pull 300mA or approx 1W for example.
When one uses a step down driver at 300mA it will regulate the voltage. In the above example it will "allow" 3.5V across the led (note though at 25C).Therefore maintaining the current at 300mA. When the led warms the current drain may be say 350mA @ 3.5V. The driver will regulate the voltage down to like 3V in order to keep the current output at 300mA
My understanding of it.
The addition of CC and CV could potentially affect this though, I’m far from being an expert in this field so I don’t know.
The drivers should maintain the set current regardless of the # of leds or their internal resistance.
Could be the leds are just getting old and losing efficiency.
After awhile the output at said current (watts) would decrease.
Or some other oddball thing like a current leak due to whatever (led to heatsink) .
Basics I know.. oddball stuff.. not so much.
accounting for LED resistance
I'm doing a simple lab (I'm a hobby EE) to reinforce my ohm's law math and learn a little about how to do proper measurements with a multimeter. I have simple circuit with a 2.2k ohm resistor conn...
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Gen 3s have an independent circuit for the violet LEDs (their peak is actually not UV (i.e., below 400nm) no matter what they call them). The only effect, if any, would be to the others on that circuit. Since they have such a low output, they won't noticeably affect PAR. They're pretty much just for fluorescent pigments anyway.
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