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# 72 volt led chip

#### KevinW

##### Member
I have an outdoor security light that has a few open led chips that I want to replace but the voltage is 72vdc and I believe .5 watt chip.
Can't seem to find a chip like that on line so I wanted to ask, are some of these chips actually 72vdc ?

A single white LED is almost always around 3 V, but it is very common to have many in series in one package.

Getting hold of odd packages can be difficult.

72 V and 0.5 W is only 7 mA, which is very small. Most LEDs for illumination run at higher currents. How did you measure the voltage? LED driver circuits usually run at approximately constant current, so if the LED goes open circuit the voltage across the LED will increase. If you measure the voltage with failed LEDs, you won't get the correct reading.

The amperage I looked at was around 300mA.
There were leds missing but I can test a lamp that still has all working leds.
There are 8 chips on 6 lamps all together , 48 chips in total.
You can see the metal contacts in the center, that's where I measured the 72vdc.
The plate on the back reads C2440-kw-27W
ac120v , 60Hz , 0.59A ,27W , cct:5000k.

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I can't see the detail, but the LEDs are almost certainly in series. I would guess that the 8 chips are in series, totalling 72 V, so that the is 9 V on each chip. You could confirm that on a working one by measuring the voltage across one LED chip. I have seen LED chips with three separate LEDs, each wired to two terminals, so the assembly has 6 terminals. It could be that you have something like that with all three wired in series.

If the plate on the back is correct, that is 27 W in total, or 4.5 W per lamp, so that is 62.5 mA at 72 V. So you are looking for LED chips that are 9 V (3 LEDs in series) and rated at 62.5 mA (or 560 mW) or more.
It is quite likely that the chips are rated to a higher current than they are being run at, so if you find some higher-rated LEDs chips that are still 9 V, they will be fine.

You are bang on, 9vdc across one led.
I'll start hunting, thank you very much for the help.

Just a question on the wattage, if I have a 27 watt light fixture and a total of 48 leds, is that .563 watts/led ?

Never mind, ... 560 mW
Thanks again.

Thanks Tony.

Those LED modules appear to mainly be used in "Sansi" brand lights, eg.

That's it, a friend had it and the chips were burning out one at a time after two years.
He was going to trash it so I wanted to see if I could save it.
I couldn't test it without soldering wires to it because of its blinding brightness.

FWIW The chips fail from excessive heat and poor heatsink interface

The heatsinks around the lamps are plastic and not metal so that likely doesn't help.

The heatsinks around the lamps are plastic and not metal so that likely doesn't help.

The LED's are over driven, so their life will be short.

The heatsink is ceramic but the lens holder is plastic.
The designer must ensure adequate heatsink on Alum. PCB with convection air flow not above the neighbouring LEDs..

If both are not done, then the unit will fail at a rate of 50% faster every 10'C rise above 25'C from Arhennius effects. So if running at mx 125'C it will fail 1024 times faster than the generic 50kh rating.

5kh is only twice as long as old incandescent bulbs were designed for when used properly with convection air flow and would fail much faster in a sealed ball.

Obviously the designer did not heed the requirements of these LEDs to get "super-long lifespan", which I seriously doubt given the surface area of the sink/W is about 5% of the area needed .

Given that it is motion sensed, it was designed for very short operating life with inadequate air flow.

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Interesting, thanks Tony.

If you look at the Big Clive on YouTube, he often modifies LED lamps to lower power to give them longer lives.

Reducing the current is just increasing the <1 ohm current sensors I*R = Vref (constant)

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