# Powering a 3W LED circuit or driver?

Freddythunder
I've been doing a lot of searching on the interwebs for the best way to power these 3W epistar high power LEDs. And then I started looking for an alternate I can afford. I hope someone can help me as I'm not too good with electronics.

I got a handful of these LEDs:
https://www.ebay.com/itm/10pcs-x-3Watt-3W-High-Power-led-850nm-940nm-730nm-Infrared-LED-IR-for-Night-Visi/253460571911
And a handful of these LED drivers:
https://www.ebay.com/itm/253527489913

I'm eventually wanting to power with car power, 12-14VDC, but for testing, I'm using a 11.1VDC LiPo battery so I know I've got enough current.

It reads that these drivers can drive "1*3W" LEDs. And I know that unlike other LEDs, the 3W LEDs don't 'necessarily' have forward voltages as it changes with temperature. That could be wrong.

I hooked up the battery to the spike end and the wires still were at 10VDC. I was thinking that maybe the load would take that down to where it supposed to be. I hooked up one LED and was blinded with super bright light. But the lead slipped off. When I could see again, I held the wires to the LED again while not looking directly at it and it seemed to be running okay, maybe dimming a little. Then there was smoke and the oh-so-familiar smell of electrical fire.

I found this driver from Canada, eh. Seems to be a good solution but a little pricey so if there's a way around it, that would be great.

What say you?

Mentor
You linked infrared LEDs. They should be deep red (for 730 nm) or invisible (850nm, 940 nm) but not white. They also need about 1-2 Volt while your LED driver seems to supply 10 V. Something doesn't fit here.

I hooked up the battery to the spike end and the wires still were at 10VDC.
The driver tries to drive 300mA, and that's not really successful through the air gap even at 10V, which is most likely the maximal output voltage. So it is normal.

I hooked up one LED and was blinded with super bright light.
Well, if you bought that as IR LED, then you should bring them back to the seller...

Then there was smoke and the oh-so-familiar smell of electrical fire.
You better run your LEDs with fixed wires and with proper cooling.

CWatters
Homework Helper
Gold Member
They do have a forward voltage, it's listed in the specification on the eBay page.

Did you have the driver connected to the battery with correct polarity?

The driver is <$1 so not that expensive? Freddythunder Thank you for the responses; I don't think I was entirely clear about a couple things.. Sorry. First, I put the wrong link in here.. I do want to get IR LEDs in the future, but need to figure out how they work with visible light first. HERE are the LEDs I'm working with: https://www.ebay.com/itm/1W-3W-High...-10000k-30000k-LED-20mm-star-pcb/321471559197 Same thing, just visible light. The smoke came from the driver and the chip on the driver has burn marks on it. The LED seemed to be working properly, the driver was burning. The polarity was correct. Since the light comes from a diode, if the output polarity was backwards, nothing would work. The ebay page states that the input is AC/DC, and I just checked now, I can hook up my DC battery backwards to the driver and still get positive DC power through the output. These ARE the drivers that are cheap ( <$1 ), I would imagine I would have less problems with the $20 driver. These small "flashlight" drivers don't have much in the way of documentation. I'm 100% sure I have it hooked up correctly because it was operational. I posted my question here because I don't know why the driver started to smoke and I've never powered an LED with 10V before without a resistor (without almost instantly burning out the LED). I'm hoping to find someone with experience with drivers like these to either tell me how they successfully used them, or call me an idiot for trying to use them - then I'll just save my pennies and by two$20 ones for my application.

At this point the driver that smoked still technically works (still registers 10V through DVM). The LED is still operational (I can hook up a 3V CR123 to it to make sure it works - not healthy for the LED long term, but good enough to make sure it still works).

Thanks again

SunThief
Just some thoughts and speculation:

3W LEDs don't 'necessarily' have forward voltages as it changes with temperature

As CWatters pointed out, LEDs do have assigned operating voltage ranges, the ones in your latest post look to be about 3.6-3.8V for the 3W version*. But it's true temperature impacts LEDs (badly). As Rive pointed out, I would get some sort of heat sinks on them. From what I've read, LEDs can easily go into "thermal runaway". They can also be susceptible to problems from turn-on surges.

[Deleted] Was thinking of compliance requirements, but on second thought that's probably not the issue here.

If you do have a few of them--play with them a little. For example, the driver output unloaded was 10V. You could put a few of the LEDs in series with the driver output and see what happens. [But there would be less potential for losing components--if you instead tried to drop several Volts with a power resistor in front of one of the LEDs. But the resistor would need to be a few Watts to handle the heat.]

............
*Note that the drivers are not capable of providing the max 700 mA current for the 3W LEDs you bought.

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Freddythunder
Thank you SunThief. I think your last comment is the most important. I did not notice that the LEDs were 700mA, and if the driver can only do 300mA then that could explain the smoke. I think I was looking at the 1W specs at 350mA.

I was also thinking that 3W at 10V would only pull around 300mA... V=WA, 10 = 3A, A=.33=333mA but I guess the power could be fluctuating too.. If it was pushing 300mA, it was still way bright. I'll try putting a few in series to see what happens I bought 10 drivers and 50 LEDs so I can lose some without crying much

SunThief
Two other thoughts:
• The specs for the driver give two ratings: input voltage DC/AC 12, and rated voltage 6-12VDC. At first I assumed the latter was just giving you the range of possible input voltages. But it doesn't actually define it either way... and it seems odd that it wrote the second voltage only showing "DC" if that were the case.
• More to the point re: your application: Don't know the driver's wiggle room. But if you intend on ultimately using a car battery (particularly if it's connected to the car), as you indicated, the voltage will range up to 14VDC or so.

the LEDs were 700mA, and if the driver can only do 300mA then that could explain the smoke.
No, it can't. If the driver is 300mA, then it'll just drive that 700mA LED with 300mA. You will get less light but that should be all.

The 3W at 300mA indeed suggests that the driver might be able to handle two (maybe: three) LEDs in serial, but... Well, do you have a datasheet? Or: could you please give us the exacty type of that eight pin chip?

Ps.:
The specs for the driver give two ratings: input voltage DC/AC 12, and rated voltage 6-12VDC.
Maybe the second voltage would be the output voltage range? That would be a possible explanation for the smoke...

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SunThief
Freddythunder
I wish. I can't find any more docs than what's on the pages. I'm used to that buying parts from China and figuring stuff out. But I can tell you the chip is MC34063A.

So how do you suppose the chip started to burn?

SunThief
Maybe the second voltage would be the output voltage? That would be an explanation for the smoke...

:-) Was just about to second guess my statement, as maybe they were just pointing out a larger range for the DC, because it doesn't "swing". Don't know...

the chip is MC34063A.
That's just a common switching regulator, not a specific LED driver. All depends on the exact schematics and the will/luck of the designer.

Try a new one with two LEDs. That should be within the 6-12V range... But we really don't have enough information for anything else but a guess.

Don't know...
We need a crystal ball

Mentor
The driver has an output voltage of 10 V = 3W/(0.3A).
If you hook up a single 3 V LED it is close to a short circuit for the driver - it will try to supply 10 V but fail. It is not surprising that the driver failed, and if that would have survived then the LED might have failed quickly afterwards from the high current and corresponding heat.

Gold Member
LED drivers are typically Current sources (the one you linked to has 300mA constant current output) with a defined output voltage compliance range, in the present case that would be 6-12VDC. Trying to drive a 3V LED, you are asking it to operate outside its range. It tried, in fact it almost committed suicide in the effort! Try driving three series connected LEDs, They should all be about the same brightness, and about half as bright as they will be when driven with 700mA.

And you will need a way to cool the LEDs. There are not any dimensions shown so we have no way of guessing the thermal resistance for cooling. A veery rough rule-of-thumb is 2°C rise per Watt with a 1 sq.Ft. surface area for cooling. If the LED module is 1.5 Inches diameter you have ≈ 3.5 sq.In. area, or 1/40 sq.Ft. That would make the LED temperature rise 2°C⋅3W⋅40 = 240°C above ambient. Clearly a cremation temperature for the LED!

Cheers,
Tom

jim hardy