Drivers for flood light keeps failing

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Ainsley Whyte

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Location
Jamaica
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Senior Electrical Engineer
I have been called to troubleshoot led flood lights for a big plant the drivers keeps failing over time very frequently voltage is 220 VAC. the lights are fed from a 220VAC secondary 37 KVA transformer 60HZ. In my country we used 50HZ could this be the reason why the drivers are failing so frequently ?
 
What country are you getting 60Hz 220vac(rms)? Is it a good solid sine wave?
 
Ainsley Whyte said:
Jamaica we used 50 HZ. However I notice the transformer is 60HZ the drivers are 50HZ therefore could this damage the drivers over time ?
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Where is there 60Hz in Jamaica? Do you have a 60Hz xfrmr on 50Hz supply? That's a no-no.

What's the actual voltage on the secondary side of the xfrmr (or on your LED lamp)?

xfrmr's will be same Hz on both sides, input freq = output freq, but a mismatched supply/xfrmr messes up voltage and coil loading (impedance).
 
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FionaZuppa said:
Where is there 60Hz in Jamaica? Do you have a 60Hz xfrmr on 50Hz supply? That's a no-no.
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yes i know that this is a no-no someone installed the wrong cycle transformer a 60 instead of a 50 therefore this must be the reason why the drivers are failing ? you agree
 
Dunno if that's the reason. If the xfrmr is getting saturated then not good stuff happens.

Possibly bad voltage, and possibly some clipping/distortion, the sine wave no longer looks like a good sine wave. I can tell you for sure, a LED drivers that use dc-dc converter inside and it's fed not good sine wave, will usually kill such driver in short time.

What's the actual voltage on the LED lamp driver? Can you scope it?
 
FionaZuppa said:
Where is there 60Hz in Jamaica? Do you have a 60Hz xfrmr on 50Hz supply? That's a no-no.

What's the actual voltage on the secondary side of the xfrmr (or on your LED lamp)?

xfrmr's will be same Hz on both sides, input freq = output freq, but a mismatched supply/xfrmr messes up voltage and coil loading (impedance).
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the voltage on the secondary side of the transformer is in the range from 220-240 vac
 
Ainsley Whyte said:
yes i know that this is a no-no someone installed the wrong cycle transformer a 60 instead of a 50 therefore this must be the reason why the drivers are failing ? you agree
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No. The transformer itself will be overstressed over a wide range of load conditions because the lower frequency at the design voltage will bring the core closer to saturation. That could cause the output waveform to be less than ideal, but not it a way that would be likely to damage the driver.
If the RMS or peak output voltage is critically low and the driver incorporates a constant power output circuit, the higher current at a lower voltage could overstress the input circuitry of the drivers, but it does not feel to me like the cause of your problem.
 
Ainsley Whyte said:
the voltage on the secondary side of the transformer is in the range from 220-240 vac
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In the range? Not likely there's a 20vac(rms) swing, but maybe. Your meter reads what voltage?

The output of the xfrmr is 50Hz if the primary is 50Hz.

Wild guess, the secondary side waveform is not smooth sine wave, and this will mess with various types of loads in bad ways. Need to scope it to be sure, but it may only get bad when the xfrmr is heavily loaded. How much load does that xfrmr see?

Might also venture a guess that the primary side is not matched to the supply voltage. What is the make/model of the xfrmr? A mismatched primary for both voltage AND Hz, bad things can happen.
 
FionaZuppa said:
Dunno if that's the reason. If the xfrmr is getting saturated then not good stuff happens.

Possibly bad voltage, and possibly some clipping/distortion, the sine wave no longer looks like a good sine wave. I can tell you for sure, a LED drivers that use dc-dc converter inside and it's fed not good sine wave, will usually kill such driver in short time.

What's the actual voltage on the LED lamp driver? Can you scope it?
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will let you know but i think is 220vac
 
FionaZuppa said:
In the range? Not likely there's a 20vac(rms) swing, but maybe. Your meter reads what voltage?

The output of the xfrmr is 50Hz if the primary is 50Hz.

Wild guess, the secondary side waveform is not smooth sine wave, and this will mess with various types of loads in bad ways. Need to scope it to be sure, but it may only get bad when the xfrmr is heavily loaded. How much load does that xfrmr see?

Might also venture a guess that the primary side is not matched to the supply voltage. What is the make/model of the xfrmr? A mismatched primary for both voltage AND Hz, bad things can happen.
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so how could you correct this without changing the transformer to a 50 HZ type ?
 
Ainsley Whyte said:
so how could you correct this without changing the transformer to a 50 HZ type ?
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If it's getting saturated, you can't fix it. The only way to know for sure is to scope it.

You could possibly correct the primary impedance, but 1st you need to ID if saturation is happening, which may occur at various times depending on how the load gets applied to the xfrmr.

Correcting primary impedance is not difficult, but not sure if you can do it or if it would be safe to do in your specific situation, you would need to have the supply turned off to do the correcting. And, it will cost some money to make the correction.

Why did they use a 60Hz xfrmr?

If all you need to do is ID the cause, then you need to scope the secondary to see if there's an issue there.
 
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FionaZuppa said:
If it's getting saturated, you can't fix it. The only way to know for sure is to scope it.

You could possibly correct the primary impedance, but 1st you need to ID if saturation is happening, which may occur at various times depending on how the load gets applied to the xfrmr.

Correcting primary impedance is not difficult, but not sure if you can do it or if it would be safe to do in your specific situation, you would need to have the supply turned off to do the correcting. And, it will cost some money to make the correction.

Why did they use a 60Hz xfrmr?

If all you need to do is ID the cause, then you need to scope the secondary to see if there's an issue there.
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How do you test that transformer is saturated
 
Ainsley Whyte said:
How do you test that transformer is saturated
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A few ways, but using an oscilloscope is the best way. You need to know how to do it to be safe.

Amp clamping a primary leg could also be used as a saturation indicator, amps should suddenly jump up when the saturation point is reached, but you need to apply load from zero to max in increments.

If you don't know these methods then it's best you seek out someone local who does.
 
A lot of good discussion about your transformer, but do not overlook other factors.

For example, what is the ambient temperature and how does that compare to the device rating?
 
GoldDigger said:
No. The transformer itself will be overstressed over a wide range of load conditions because the lower frequency at the design voltage will bring the core closer to saturation. That could cause the output waveform to be less than ideal, but not it a way that would be likely to damage the driver.
If the RMS or peak output voltage is critically low and the driver incorporates a constant power output circuit, the higher current at a lower voltage could overstress the input circuitry of the drivers, but it does not feel to me like the cause of your problem.
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I agree with this.
The strength of the magnetic field applied to the core is proportional to the volt-seconds at the primary winding. Obviously there will be 60/50 = 1.2 times more volt-seconds in a 50Hz positive or negative half-cycle than for a 60Hz one. If you integrate the sine wave voltages to get the volt-seconds, a 50Hz waveform will reach the same volt-seconds as a 60Hz half-cycle does in only 132° instead of 180°. So if the transformer was right on the edge of saturating with 60Hz applied, then with 50Hz it would saturate at 132° into the half-cycle and at that point the output voltage would fall to zero until the next half-cycle. Now sin(132°) = 0.745 and so in this case the voltage waveform on the transformer secondary would drop when the sine wave falls about 25% after reaching its peak value. In reality the transformer will have some design margin before it saturates and so the voltage should drop later in the waveform.

I would think an input rectifier in the driver should still tolerate this type of distorted waveform without damage, and possibly without much other effect if the rectifiers are only conducting near the voltage peaks anyway.

The only mechanism I can think of that might cause damage is if there were shunt capacitors at the driver input for EMI filtering or the like, and the fast drop (high dV/dT) in the applied voltage induced relatively high currents in such capacitors. But that's probably a stretch. The only way to know for sure would be to do a failure analysis.
 
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