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Author Topic: Exploding resistors  (Read 367 times)

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Offline SirRawThunderMan

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Exploding resistors
« on: November 02, 2020, 04:58:19 AM »
So, I've got a bit of a conundrum at hand. (THE CURSED BUILD CONTINUES)



That was a 1.5ohm, 2W SMD power resistor, connected to the red LED on my tri-cree from a Proffie 2.2. According to three separate LED resistor calculators and my own math (R=(Vs-Vf)/I, so (4.2-2.95)/1: 1.25 ohms, and P=(Vs-Vf)xI, so (4.2-2.95)x1: 1.25W), that was the correct resistance and power for a red tri-cree with a forward voltage of 2.95V at 1A (measured with a power supply, not just read off the data sheet.)  In fact, most recommended a 1.5W resistor, but I couldn't find one in a 2010/5025 package, so I bumped it up to 2W which was available.

And it overheated and blew in about 30 seconds. I'm trying to work out why, and how to fix it.

I replaced that array with a second one, and while that didn't explode, the red resistor did overheat rapidly. 0-95C in ten seconds. I replaced it with a non SMD metal film resistor, which took a little longer (90 seconds, approx, not surprising given the extra mass of a full size resistor) to heat up, but it got to 80C.

if anyone's got any ideas, I'm all ears.
« Last Edit: November 02, 2020, 09:24:13 AM by SirRawThunderMan »
Better late than never.

Offline SirRawThunderMan

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Re: Exploding resistors
« Reply #1 on: November 02, 2020, 07:05:54 AM »
Right, so I measured the amps going through each LED, as well as the voltage, handily letting me calculate the actual wattage. AxV=W, so R: 0.8Ax 3.84v= 3.072W, G:0.6Ax3.84V=2.34W, rB:0.55Ax3.84V=2.112W). And that answered one question: the reason the resistors are overheating and exploding is because the proffie is driving the LED with more power than the resistor is specced to handle.

Now, the next question is why?
Better late than never.

 

retrousse