At the TechShop in Chandler, Arizona (techshop.ws) they have a "Junk" bin. As a result of this there are a lot of useful things especially electronic devices. The upside of this is that the part is free but the down side it is difficult to know what the power requirements are. In this instructable I will go over how to test things safely and provide some tips to help you out. Keep in mind that this form of testing really applies to things that you can directly sense with one of your five senses such as LED's.
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Step 1: Turn All Knobs So That the Are All Zero
Keep in mind that you are dealing with a DC power supply so you need to zero out all the knobs before you turn on the device. Failure to do so can cause serious injury or death.
Step 2: Connect Your Device
It might sound weird but you should connect your device (follow the directions regarding your device and ask experts around you). The reason you do this is because everything is zeroed out.
Step 3: Turn on the Device and Start Incrementing
This is the fun part where you try to power up your device. Initially it will be ampere will be zero as well as the voltage. Notice the 'CC' red led is on. This means that you have reached the maximum allowed current that you have defined and in this case it is zero. Turn the current knob until this light is turned off and the 'CV' green led is on. From here slowly turn up the Voltage dial until the desired outcome is reached. Also you might have to adjust the current knob a little bit at a time, because again, as you increase the voltage you also increase the current. Again to be safe increase the current knob until the light changes. Once the desire result is reached note the voltage (current does not matter to much since you need the correct voltage in order for the current to flow anyways).