"10 watt" LED

Yup and with flaky chips that laugh at their spec sheet the bell-curve voltage/ma/lumen output relationship can assume the absurdity of Monte Hall, and let's-make-a-deal.

Lin, is whom set me up with SHARP chips. But they cannot compete with scumbag low-cost-at-a-high-price specials in eBay. Many 10-watt chips exhibit multiple colors and intensities throughout the plate.

CREE chips are sensitive and utterly unforgiving about drive current.

A sort-of-clue
A company that offers 365 nanometer grade ultra-violet chips usually is a lot stricter with chip quality. Costs more but the chips are uniformly top notch.

You mentioned the 20-100 watt family of chips. This is where I spend time with my lab power supply between 34-36 volts. The Sharp units seem to prefer 34.7 volts as the top of the bell compromise.

To suggest a Chinese company is going to use top drawer chips then custom power them to an optimum compromise would be really stretching it.

The Karma Sutra of Chinese LED philosophy seems to be "Buy an X wattage chip then drive it at 60% so maximum savings are realized on the cost of heat sinks. Frugality to the point of running the chip above the thermal upper limit.

Down here, one of the pastimes is noting exactly how the new LED streetlights have failed. flashing, mass area blowout, intermittent operation wotta hoot.

Then there are the new cars with interesting faults in LED tail lights.

I'll stick with my severely controlled engineering environment - thank you...

GordonThree wrote:
3s 3p led array

Vf(typ) 3.3vdc per chip, x 3 in series = 9.9 volts. Let's round to 10

Ohms law P=V x I ... So 10=10 x I, so I = 1amp

So let's say 13v supply voltage means a resistor needs to drop 3 volts.

Ohms law V=I x R ... So 3=1 x R, thus R=3.3 ohms (nearest easy value)

Ohms law P=I²R ... So P=1 x 3.3, thus P=3.3 watts

I'm a bit rusty... What did I miss?

Of course you can under drive the module to reduce loss but also output.

Technically, your math is right but your ASSUMPTIONS ARE WRONG bringing the entire equation into error.

Your assuming 3.3V per diode, that is not correct.

White LEDs can be had with voltages ranges from 3.1 up to 4.1V depending on the different materials used to make the diode junctions.

The 10W COB that the OP has, is most likely similar to the ones I have which are specd at 11.1V of the series string, that puts the diode junction at 3.7V.

Now, since I have messed with 10W, 20W, 30W and 50W versions I can't say for sure at this time the exact max current for each, I would have to dig around to find the manufacturers spec sheet and my notes.

I can tell you this, the 10W versions ARE 11.1V for full brightness and current draw. The 20W, 30W, 50W require 34V as a min voltage which to operate from 12V would need a booster power supply.

I did retrofit a couple of my TTs outdoor porch fixtures with the spare 10W versions since I didn't need a boost regulator.

Unfortunately, it IS a very dreary and wet evening tonight and the rain is forecasted through Sat so I am not about to bother getting a ladder out to pop the lens off to verify the resistor I used..

My point to you is a couple of watts heat wasted by a resistor is not in any way shape or form "substantial" compared to the wattage consumed by the COB.

Statistically speaking it can be said that the difference IS NOT STATISTICALLY SIGNIFICANT, since the increase in loss is very small compared to the overall power used by the entire device.

People tend to forget that a switching power supply regulator does indeed WASTE energy in the form of heat. It just does it a a SLIGHTLY LOWER AMOUNT.

Typical switching supplies often have efficiency levels of 80%-85%, some may reach 90%-92% but not very many do. That means a switching regulator will waste 15%-20% of the power that goes into it as heat..

If the power wasted by the resistor was EQUAL OR MORE than the COB then I would consider that to be STATISTICALLY SIGNIFICANT.

And YES, I ERROR on the safer side by UNDER DRIVING THE LED. There is a point where the current increases rapidly and yet the light gain is extremely small, at that point pushing it to max yields very little light gain and severely reduces the operating life..

That is intentional, and vastly increases the life of the LED (or any device for that matter).

This also allows for the fudge factor when things don’t go as planned.

MEXICOWANDERER wrote:
What is missing is compensation for a two volt spread in supply voltage. This is the primary justification for using PWM rather than pure resistance

x2 ... active circuitry, either linear or switching is much better suited to an automotive environment that is an RV. I designed my personal fixtures to handle at least 18 volts input, with 35 volt ceramic caps on the input stage.

Lets not even get started on load dumps and other transients that SAE specs worry about :)

"And furthermore (Jacques Clouseau :)"

May I suggest bench testing samples using a precision power supply?

The 10 watt chips are The Wild West. Take 2 different samples DUT

Apply threshold voltage to illuminate: Note value.

Apply each to a given heat sink...

Note Delta T at recommended drive current...
...then back off the high temp DUT to = temp of the lower chip

Does the illumination seem to be the same?

This exposes (strengths - weakness) in manufacturing techniques

What is missing is compensation for a two volt spread in supply voltage. This is the primary justification for using PWM rather than pure resistance

3s 3p led array

Vf(typ) 3.3vdc per chip, x 3 in series = 9.9 volts. Let's round to 10

Ohms law P=V x I ... So 10=10 x I, so I = 1amp

So let's say 13v supply voltage means a resistor needs to drop 3 volts.

Ohms law V=I x R ... So 3=1 x R, thus R=3.3 ohms (nearest easy value)

Ohms law P=I²R ... So P=1 x 3.3, thus P=3.3 watts

I'm a bit rusty... What did I miss?

Of course you can under drive the module to reduce loss but also output.

GordonThree wrote:
Lol

I am not sure what you are "laughing" about..

After all, it was YOU that made the statement "The downside to a resistor dropper is extreme energy waste, especially for a high power LED."


.7W extra compared to the 4W the COB consumes is not an "extreme energy waste"..

And YES, those switching regulators WASTE .5W as heat as they are not 100% efficient, 90%-92% at best.

I am laughing at YOUR statement, its pretty darn funny when folks think they know electronics..



Thanks for the comic relief, I needed that after dealing with stupid wet behind the ears engineers that make twice the money that I make, fixing their stupidity..

Lol

The LED in that light is known as a "COB" or Chip On Board LED.

Consists of 9 1W LEDs.

You will see that there is three rows of three LEDs, the LEDs in each row are in series and the three rows are in parallel.



So, no, it doesn't "consume" 10W, it only will consume 3-4W but give the light of about 10 watts worth of LEDs in lumens.

The little power supply is a constant current switching supply which gives the light a broad input voltage of 10V-30V DC.

It was never designed to be dimmable and to make it dimmable you would need to replace that power supply with either a resistor or a constant current supply which has a adjustable output.

I have played with a few of these COBs and they actually are pretty darn good, I have two similar 10W to yours mounted on my tractor for flood lights on the backhoe. Have had those about 3-4yrs now and they do get used a lot.

Also have bought a few of the bare COBs in 10W, 20W and 50W versions.

Had a super 8mm film projector that used a super rare and expensive 36V 80W bulb that blew out while I was in process of transferring my parents super 8 home movies.

Bought one bulb at $80 and the filament was not centered properly and only would light the bottom 1/3 of the film..

Returned that bulb and got another one, it still had a issue with the filament not centered, so it didn't fully light the film but was better than the first one..

So, I took a stab at building a bulb from a COB LED.. tried 10W, not bright enough, 20W, 30W better but not bright enough, 50W almost perfect match for brightness, slightly darker than the original bulb but doable.

The 10W and 20W can be run from 12V, the 30W and up require min of 30V to light them so to use those with 12V you need a 12V - 36V booster regulator..

The only downside I have found with the early COB design is the color temp selection was outside the projector bulb color temp. I was able to buy specially made color gel films to correct that..

For my projector project, I also bought a collator lens to focus and intensify the light output.. Made a huge difference in the film brightness.

As with any of these high power LEDs, heatsink IS a must, never attempt to run without the chip firmly planted to a chunk of metal.

As far as a resistor wasting power goes, yeah, it will but in reality it is extremely low..

For instance that 10W COB only needs about 10V to start glowing, and around a max of 11V for full rated brightness, current was specd at .370A.

A 12V RV system can get to about 14.4V while charging so we need to drop about 3.4V.

I used a 10 Ohm resistor to accomplish the drop.

That resistor I selected only will dissipate 1.2W of heat..

The switching regulator that is used in those lights typically will consume about .5W of wasted heat..

So, yeah, big deal, using a resistor will "waste" an additional whopping .7W!!!

I suspect that the regulator has bought the farm, to check this you can simply disconnect the regulator board, sub in a 10 Ohm 2W resistor..

If the COB lights fully then the culprit was the regulator..

The advantage of using a resistor is it is cheap and you now can DIM the LED. Just be aware that the dimming range is pretty small since the COB will need at least 10V to start making light..

You can upgrade the COB to a higher wattage, just be aware that to do so will require a boost regulator and you still won't have dimming.

Seventeen moolahs for a ten watt driver is beyond what my wallet is willing to part with. And yes, a person has to be careful when buying light emitting diodes or accessories off of eBray.

None of the drivers I purchased have failed from the vendor listed above. Near 100% chip failure of integrated housings/chip assemblies.

The SHARP 30 and 50 watt chips I purchased blow the doors off of the chips I purchased from Mickey Mouser. Better sunlight color, cooler running, and more uniform segment illumination.

For 120vac to 36 volt conversion I use ventilated power supplies. That way I can tweak to match ma to specifics. For instance over my new work bench I backed off voltage to 34.4 from 35.8 (4%) on a 50 watt Sharp chip.

So, as far as I am concerned "blanket statements" about LED components are risky. A Truism however seems to be any 120 vac LED lamp assembly from China should be treated like the electrical components are sub-marginal.