| Electronics > Beginners |
| Some noob questions |
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| Mr D:
***WARNING*** Extreme noob question alert! I've only been messing with electronics for about a week and i'm really struggling to get my head around the basics. I bought myself a Fluke 115 multimeter as a starting point. So, i grabbed a selectable voltage wall-wart i had lying around and started to measure it. If i set it to 3V, i measure around 2 amps of current. If i change the voltage to 12V, i still measure around 2 amps of current. Sooooo, my first (of many) noob questions is: if 3V and 12V both push 2 amps of current down the wire, why would you need any more then 3 volts? ------------------------------------------------- And one other quick, forum related question: is there any way to subscribe to a topic, so that i get an email when there's a reply? I can't see this option anywhere when i post or reply. |
| Ice-Tea:
Most electric stuff has a certain working voltage. A fan, per example, would like 12V and will not work properly at 3V. On the other hand, an IC may have been designed for 3V3 and will let out the magic smoke at 12V. Note also that by measuring the output terminals of your wallwart with your DMM set to measure current you are effectively short-circuiting the terminals. |
| Mr D:
Thanks, but that doesn't answer the question in my noob-brain. The current is what does work in your target device, right? If the current is the same, whether i set it to 3 or 12V, why is 12V necessary? About your other point: why is short-circuiting the wall-wart a problem? |
| Ice-Tea:
Why does a car run on diesel but not on gasoline? Because that was what it was designed for. But to answer your question: one of the things you're not taking into account is power. 2A@3V gives you 6W but 24W at 12V. Short-circuiting *anything* is a problem. In essence, you are using an-almost-zero-ohm resistor as a load (aka short circuit). Electronic sources that are well designed will provide their maximum current (in this case 2A) and the output voltage will drop to almost zero (check ohms law and you'll understand why). Less well designed sources will blow up, overheat, be in hickup mode, catch fire, blow the fuse of your DMM... |
| Old Printer:
From another noob with a bit more time. Current needs to be flowing, doing something. To measure current (amps) you need to have a circuit (complete) where the current can flow and do work, like light a bulb or turn a motor. All you can really measure like you are doing is voltage (potential). |
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