# How can I find out a components voltage rating and amperage draw?

I bought a whole bunch of components for mounting on a circuit board (I'm new to electronics and I'm just experimenting at the moment) - things like LED's, small microphones, buzzers, very small speakers, motors, displays, IC's, Op Amps, etc.

I'd like to know the method for finding out what the power requirements for each component is. What tests can I do with my multimeter to determine the needs of each component without damaging the component?

The only method that comes to mind (with my limited knowledge) is to attach a DC power supply, such as a 9V battery or a 4.5 V battery pack and run the current through a resistor in series with each component, starting at very high resistors (MΩ) and working my way down to less and less resistance, all the time monitoring the component to see of it is operating. This seems very imprecise and is just trial and error until I get in the ballpark of what each particular device needs.

Is there a better way of doing it? Does it have something to do with measuring the resistance of each device?

I know I can use Ohm's Law for V/R = I where V = voltage of battery pack and R = resistance of component, but that doesn't really tell me the requirements of the component - or does it? The motor for instance runs on 2.8V and 8.2V - just faster in the 2nd case. Things like the displays are much more prone to damage and I can't just run some random voltage through them and hope for the best.

• You look at the components datasheets. Commented Jan 26, 2017 at 11:44
• Read the part numbers and look up the data sheet for each. Would you buy a spice rack without markings on each spice bottle? Commented Jan 26, 2017 at 11:58
• I can only repeat the chant here.....data sheet....data sheet....data sheet. Commented Jan 26, 2017 at 12:33

You are right, measuring a components characteristics has some error, and at best only tells you what that one component at that time and that temperature can do. What you really need to know to design circuits with components is the maximum range of various parameters.

This is why each component should have a accompanying document called a data sheet. The manufacturer of the component creates the datas sheet, and usually makes it available on their web page.

There is no substitute for using the datasheet values in proper circuit design.

For one-off or hobby purposes, you can take a few guesses with parts that are similar across manufacturers. For example, 0805 resistors can usually dissipate about ⅛ W. If you have a bunch of unknown 0805 resistors, you should be quite safe keeping their dissipation to 100 mW and the voltage across them to 50 V.

Just about every LED can handle 20 mA. Modern LEDs are efficient enough that 10 mA is usually plenty for indicator use. That really should be OK with pretty much any LED you're going to find. LED voltage is also a function of the color, due to physics. Common "green" LEDs usually drop about 2.1 V, for example, red ones around 1.6 V, IR about 1.2, etc.

The power dissipation of a component is largely a function of its package and geometry. You can therefore take reasonable guesses about the dissipation capability of simple components in common packages by looking at datasheets of those similar components. Still, that's no guarantee, and would be irresponsible engineering if done professionally or for a production product.

More complex parts are more unique, and there is less you can infer from similar parts from other manufacturers.

Go back to whoever you bought the parts you have from and ask for the data sheets. If a component is marked with a manufacturer and part number, then go to that manufacturer web site and look up the datasheet.