Hi there,
You have helped me out in the past, and I am hoping you can do so again. I have a rather small resistor with only two bands. The power source are 3x 1.5 AAA batteries and it is powering an LED that flickers to make it look like a flickering candle. Below is a picture of the resistor that I am trying to replace. Any thoughts or ideas would be greatly appreciated.
Thank you!
Dan M.
Hi dan.mastro.
Can you show the board where you desoldered the resistor?
Hi Adam,
Thank you for the quick response. There is no circuit board; the resistor is just in line between the on/off switch and the batteries.
Dan M.
Hello,
After some checking around this looks to be an 8Ohm resistor but not real sure the tolerances. From our inventory we had 1 reasonable match with part 541-CW0058R000JE73CT-ND and worth a look. I have this part on the link below.
Thank you
Ryan
Really tough to figure out the value from your images.
Based on that description, it seems likely that it’s just a current limiting resistor meant to protect the LED from being damaged from over-current.
There are a couple of things one can do to try and deduce the value of the resistor.
The simplest would be if you happen to own a bench-top power supply. If so, you could connect the power supply directly to the LED, starting at zero volts, and very slowly and carefully increase the voltage until the LED operates “normally”. Make note of that voltage and the current draw at that voltage.
Then using that current, and the difference between the voltage you measured and the 4.5V max voltage of your three batteries, you can use Ohm’s law to calculate the resistor value that would drop the necessary voltage with the known current.
Just as an example, if the LED required 2.9V and 0.020A, the resistor required would be about 80 Ohms (R = (4.5V - 2.9V) / 0.020 = 80Ω).
The other method that you could try if you don’t have a bench-top supply would be to test with resistors of decreasing value until you find one which allows it to function properly. You always start with a high value so that the current will be on the low side rather than the high side. Once you get down to a value where it just starts to work at full voltage (4.5V), then you drop the resistance by a bit such that it will still work with a somewhat lower supply voltage so that you are able to use a bit more of the batteries’ capacity.
This last method, of course, would require having many resistors on hand to test. Alternatively, if you have a multimeter to measure resistance, you could do the same thing with a potentiometer and just measure the resistance value at which the LED functions, and either keep the potentiometer in circuit or replace with a fixed resistor of the resistance value you measure on the potentiometer.
Thanks, everyone. All of this was very helpful!
