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How to test the forward voltage/amperage of an unknown componant?
Lets say for instance I had a red LED. I don't have any papers about the ratings of the componant so I don't know what volts or amps to put through it to make it run at optimum, while preventing it from being destroyed.
Is there some kind of test that you can do with standard electronic equipment to determine how to run it. This isn't just for LEDs, what about a small electric motor used in vibrating toys or the oldstyle games controllers?
Most motors are rated for a particular voltage, and as long as you keep the supply voltage at that voltage or below, the motor will not draw so much power that it overheats. The power limiting aspect of the motor is the resistance of the windings. P=V squared / R. The problem is that you won't know what that maximum voltage is. Look carefully for writing on the motor.
An LED is different. Some LEDs contain an integrated resistor that will limit the current sufficiently as long as you don't go over the rated voltage, just like the motor.
But most LEDs are designed for an external resistor to limit the current. In that case, other than burning out a few of them, there is no way to measure what power will be too much for the LED. Without an external resistor, an LED will draw more current than it can dissipate and will fry.
Basically, whatever component you are dealing with will draw a certain amount of current when supplied with power. Because of limits in heat dissipation or current carrying, the components will be damaged by too much power. There is no way to measure what that is without burning a few out.
The example that will make this most clear is a fuse. What is the rated amperage of a fuse before it blows? You can't measure it. If you measure the resistance of a 5amp and a 15amp fuse, you won't see a difference. If you put power through the fuses, you won't see a difference in performance, until you put more than 5 amps through the fuses, in which case the 5amp fuse will blow.
What you can do is look for labels and make assumptions. If the motor comes from a toy that holds two AA batteries in series (1.5volts each), then you can be confident that the motor will not burn out at 3 volts.
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