Burning out a resistor

RCatR · Jul 28, 2006

I have some "limiting" resistors rated for 4Watts @ 1.2 Ohms, I will be using them to limit the power coming from 3 alkaline C cells to a UXOL K2.

Should I heatsink the resistor or will it be OK floating around inside the maglite?

With the resistor 670mA is measured at the tail, without it 1670mA is measured at the tail, so it is essential that I keep the resistor in my design.

chesterqw · Jul 28, 2006

wow....you better heatsink it too.

mpf · Jul 28, 2006

1.2 Ohms at 0.7A is 0.58W
You will not need heat sinking for a 4W resistor just insulate it and let it float.

RCatR · Jul 28, 2006

if i run two resistors in parallel to drop the resistance down to .6 Ohms, will it sitll stay at 4Watts regulation?

mudman cj · Jul 28, 2006

If you mean - will using this configuration keep the resistors dissipating less than their rated 4W each, the answer is yes. Each resistor would only dissipate about 0.3W give or take depending upon the current (0.3W assumes about 1A total or 0.5A through each resistor). Heat dissipated by a resistor (W) = current (A)*current (A)*resistance (Ohms), usually written as P=I^2R.

Handlobraesing · Jul 28, 2006

RCatR said:
I have some "limiting" resistors rated for 4Watts @ 1.2 Ohms, I will be using them to limit the power coming from 3 alkaline C cells to a UXOL K2.

Should I heatsink the resistor or will it be OK floating around inside the maglite?

With the resistor 670mA is measured at the tail, without it 1670mA is measured at the tail, so it is essential that I keep the resistor in my design.

Always design with a factor of safety. 0.67A with resistance of ammeter in series could mean around 0.8A without, depending on the internal resistance of the meter.

If you consider new batteries, it could be even more, so I would design for a factor of safety of 1.5x current.

0.67 x 1.5 = 1A. 1^2 x 1.2 = 1.2 watt. You could use 1.5W-2W resistor to keep it more compact and glue it down to the side so it won't have to be dangling.

Burning out a resistor

RCatR

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chesterqw

Flashlight Enthusiast

mpf

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RCatR

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mudman cj

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Handlobraesing

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