Author Topic: 200w LED flood  (Read 6615 times)
Ash
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Re: 200w LED flood « Reply #15 on: June 23, 2015, 12:11:01 PM » Author: Ash
The entire lantern is inadequate, starting with the 1KW MH claims, then going into the glued drivers (want to mount an electronic ballast in a FL light with glue as well ?), and finally the cooling. No surprises here....

The gold pastes are more for looks than for function, actually, they are completely awfull in function. They do not have any advantage over the best silicone-based pastes, but the silicone ones form much thiner layers, dont conduct electricity, and dont stick with the strength of a weld when time comes to replace them

The heat can be expected.... Power drop happens as the LEDs heat up and their forward voltage drop falls, while the driver keeps the current the same
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Medved
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Re: 200w LED flood « Reply #16 on: June 23, 2015, 01:11:59 PM » Author: Medved
@Medved, each LED has its own driver/ballast, there are four of them in each fixture. I will be installing these lights today, after testing I found they are much closer to a 400w MH, maybe even less light than that. After running for an hour or so, the back of the fixture gets VERY hot, to the point where you cannot touch it for more than a couple seconds.

You CAN touch it for second or two means, it is not hotter than about 70degC. And you can not hold it longer, that means above 50degC, so pretty were expected...

Kill-a-watt reads 207w for the entire fixture when first started cold, after an hour of operation that drops to 173w. Why is that?

The ballasts are a constant current sources, so maintain the constant 1.5A current, whatever the actual voltage does. It is electronic controlled and that uses to be really constant.
That means the actual power becomes proportional with the voltage: 25V would lead to 37.5W, 36V would lead to 54W.
Now the LED's are semiconductor diodes in the first place, so their electrical behaviour conform to equations the diodes use to follow, especially the forward voltage having negative temperature coefficient. With silicon this uses to be about 2mV/K, with blue LED's it uses to be about 5mV/K (if I remember well). There are 10 LED's in series, so it means lets say 50mV/K of temperature difference.
Now we have calculated the operating temperature to be around 65degC, what means 40degC above the room temperature on the LED base. I would expect about half of that internally, so total 60degC difference.
So as you conect the power, by heating up the voltage will drop by 60degC*50mV/degC=3V. So when it started at 33V, so 50W, after heating up it ended at about 30V, so 180W.
It does explain at least part of the difference.
The other part may come from the ballast:
To prevent the device from overheating, many LED ballast controllers do contain a feature called "Thermal fold back". What is does: It senses the temperature and when it approaches set limit, it starts to reduce the ballast power, so the generated heat.
The aim is to provide reliable thermal protection, while avoiding complete cut offs (as the classic SMPS thermal shut down does), so it maintain the device operating.
Now as the ballast is operated above it's ambient temperature rating, it may be it is exceeding the 70degC surface temperature (actually the limiting factor would be about 130degC on the ballast IC chip) and so the power reduction kicks in.

Or other reason may be there: The ballast design is made cheap and so instead of proper reference (as part of a dedicated LED ballast control IC they may use some generic DCDC converter chip with simple current control feedback circuit), they use just a Vbe threshold voltage to regulate the current (let a simple NPN to sense the voltage drop across the current sense shunt resistor). And that has the habit of a negative thermal coefficient as well (the famous -2.1mV/K), transferring that to the power decreasing with the temperature increase (about 0.37%/degC, what means about 5/6 of the current when the ballast temperature rises by 50degC; pretty well match your observation). Actually I would see nothing wrong with that approach either, juyst the light output would vary with temperature a bit more than the real constant current and thermal fold back.

For the heat transfer compound: Whatever the color is, the modern ones tend to act as glue, so once you snap the thing off, you have no other choice than clean the surfaces and apply new compound.
The silicon grease alone is not good for this, it has quite high thermal resistance (it works only on really accurate flat surfaces in very thin layers, but here the heatsink surface is very raw). Thermally good are the metal filled compounds (usually sold in computer shops), but those are electrically conductive. Second best are the Zinc oxide based ones, again sometimes sold as accessories for CPU heatsinks or so.
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Lanternbro
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Re: 200w LED flood « Reply #17 on: June 23, 2015, 04:56:40 PM » Author: Lanternbro
@Medved, each LED has its own driver/ballast, there are four of them in each fixture. I will be installing these lights today, after testing I found they are much closer to a 400w MH, maybe even less light than that. After running for an hour or so, the back of the fixture gets VERY hot, to the point where you cannot touch it for more than a couple seconds. Kill-a-watt reads 207w for the entire fixture when first started cold, after an hour of operation that drops to 173w. Why is that?

Might be reacting to temperature increase by reducing power.
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BlueHalide
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Re: 200w LED flood « Reply #18 on: June 24, 2015, 12:13:57 AM » Author: BlueHalide
Thanks for the info, I thought the heat buildup probably affected the power. I installed half (5) of these fixtures today, and all worked except one LED module in one fixture was flashing (driver failure I assume), Ive got a feeling that the one flashing LED is a harbinger of things to come for all the fixtures. Also, I found it interesting that all four LEDs in each fixture are ever so slightly a different color, a camera doesn't pick it up, and its only noticeable to the naked eye if youre looking for it, but some are slightly cooler, or warmer. The manufacturer is shipping out a free driver for the faulty one.
And the sad thing is, this installation may actually be initially brighter than the existing MH setup, simply due to the MH fixtures being so poorly maintained. None of the MH lamps I removed today were even remotely within the average rated life, and one exploded so long ago without being replaced that the ignitor also failed due to continuous running for years trying to strike the ruptured lamp. Two of the 400w lamps were also in that "glow" state where the dim green glow wasn't any brighter than a 25w incandescent. Not to mention the fixture's lenses were super dirty and blocking a lot of the light produced by the EOL greened-out and pink lamps. I plan to save and restore some of these fixtures. Some cleaning and much needed maintenance of these quality MH floods was all this guy needed, but nope, everybody wants cheap, failure-prone, LEDs these days
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Solanaceae
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Re: 200w LED flood « Reply #19 on: June 24, 2015, 02:38:02 AM » Author: Solanaceae
Good to see that they allowed you take some fixtures home with you.  :a_mh:   Also good to see that they're compensating for the broken LEDS driver. I know the slight difference in the led color temps. I noticed that some LEDS in a flash light are bluer and some are pinker than the others. It's like mercury vapor color Change.
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