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Constant current LED drivers - faulty, flashing panels

Cirkit

Oct 28, 2015
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I have come across a few faulty LED drivers which cause the LED panels to flash on and off. Often this occurs after the driver/panel has been left switched on for a while.

I've opened the drivers up and noticed some swelled capacitors - usually on the primary side i.e. the main 400V capacitor.

Instead of constant voltage, these drivers are constant current - typically 33-40V at 1000mA output.

How can I test that replacing the capacitors has solved the problem on the bench without the LED panel? If I connect a standard 240V halogen lamp or an LED version, the lamps just flash on and off.
 
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duke37

Jan 9, 2011
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R = V/I
so 35V 1A,, R = 35
Power = V*A = 35W
so you will need a big fat resistor of say 33Ω or less as your load.
 

BobK

Jan 5, 2010
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What id the forward voltage of the LED string? It sounds like you might be over stressing the driver.

Bob
 

Cirkit

Oct 28, 2015
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so you will need a big fat resistor of say 33Ω or less as your load.

When you say 33Ω or less, how much less? Would a halogen lamp be too low resistance?

What id the forward voltage of the LED string? It sounds like you might be over stressing the driver.

Bob

I'm not sure as it's too large to measure using the diode range on a meter. I'm guessing somewhere between 33-40V typically?
 

BobK

Jan 5, 2010
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Guessing isn't good enough, it must be within the range of voltages specified by the driver.

You can power it on on a working driver and measure the voltage across it with a voltmeter. You should also check the current. If the current is not the rated output current or the voltage is out of the rated range, it is not a suitable driver for that LED panel.

Bob
 

Cirkit

Oct 28, 2015
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Guessing isn't good enough, it must be within the range of voltages specified by the driver.

You can power it on on a working driver and measure the voltage across it with a voltmeter. You should also check the current. If the current is not the rated output current or the voltage is out of the rated range, it is not a suitable driver for that LED panel.

Bob

The drivers are correct as the manufacturer has supplied some identical model replacements and they have been working fine for over a year with the same LED panels.

I just want to determine the cause of the fault and repair the faulty drivers to have as spare.

Most LED panel drivers (across different makes) seem to have the same specification so I assume, the panels are built to a standard - at least in Europe?
 

duke37

Jan 9, 2011
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I have not used current controlled supplies.

A voltage controlled supply should not be fed into a low load which demands too much current.

A current controlled supply should not be fed into a high load which demands too much voltage.

A halogen lamp will go up and down like a yo-yo in resistance as it heats up and cools down. On a voltage controlled supply this stabilises the current. On a current controlled supply, I would think that this would give instability.
 

BobK

Jan 5, 2010
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Let me rephrase.

How did you pick this driver for the this LED panel? The way one would ordinarily do that is to know the rated current and forward voltage and then pick a driver that is compatible. How did you do this without knowing the forward voltage?

Bob
 

Cirkit

Oct 28, 2015
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A current controlled supply should not be fed into a high load which demands too much voltage.

A halogen lamp will go up and down like a yo-yo in resistance as it heats up and cools down. On a voltage controlled supply this stabilises the current. On a current controlled supply, I would think that this would give instability.

I have tried it on both a halogen and LED lamp rated at 240V but both flash on and off. I supose both of these present a high load.

Let me rephrase.

How did you pick this driver for the this LED panel? The way one would ordinarily do that is to know the rated current and forward voltage and then pick a driver that is compatible. How did you do this without knowing the forward voltage?

Bob

The drivers come supplied with the panels. They are designed to work with them.
 

Bluejets

Oct 5, 2014
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I have come across a few faulty LED drivers which cause the LED panels to flash on and off.

We strike this on a weekly basis usually with light fittings with multiple LEDs.
Just put it down to crap (cheap)driver units, even though the fittings cost around $70.
Not worth repairing as the driver is unavailable as a part and it has odd parameters that nothing matches.
Way of things....
 
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