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Say I have an unknown led light, independently several person know it could be 12v or 24v or 110v even 220v
Say It's rated for 9v (and you dont know), let's say you start applying fewer volts until it start turning on and stronger, but how can you know the PROPER and CORRECT voltage?
Does it apply for a small motor? Rated say at 6v but you think it's rated at 12v or 9v.
What's the rule resistance? watts? amps?
Thanks in advance
Here is a sample link which addresses this thing:
https://www.micromo.com/technical-library/dc-motor-tutorials/motor-calculations
And to be considered: For a DC motor which run below its nominal voltage has slower no-load speed and a lower stall torque. This not cause any problems with the motor. If anything, the motor will last longer because it won’t be subject to the same level of stress, heat, friction and general wear as it is when running at the full nominal voltage.
And if it runs above its nominal voltage, it is going to magnetically saturate the steel in the motor’s core. This increases the current drawn causing the motor to run hotter and shorten the motor’s life.
Rated voltage is chosen or defined based on material and/or component properties and also on endurance tests of multiple samples.
Therefore, without knowing what's in the "black box" you cannot know the rated voltage.
Without having a number of samples, you cannot know test/deduce what the rated voltage is.
E.g. different LED's with the same voltage rating (can) have different intensities. If you apply the rated voltage to a ultra bright LED and apply an overvoltage to a 'normal' LED, they may have the same intensity. But the normal LED may get damaged due to the overvoltage.
So, checking the intensity of LED's cannot be used to trace back what the rated voltage would have been.
The current/voltage chart of the LED is somewhat J shaped: LED conducts much more (and emits light) above the certain threshold voltage. This voltage is about 1 V for infra red, 1-2 V for the visible light and can be even higher for UV LED. The operating current of the LED should normally be above that threshold while it is not obvious how much can you drive it up. You can take a current vs voltage chart with a suitable milliamperemeter (0 - 50 mA range should work for the most LEDs) and regulated 0 - 4 voltage supply, start from the 0 voltage and do not overdrive. You can do this safer if you have a second voltmeter: put a 100 ohm resistor between power supply and LED and measure the voltage directly on the LED.
It is more tricky if the thing has multiple LEDs and additional electronics inside. But it this case it is a device, not a component. It should have some name, or number printed on it that may tell more if googled on the web.
