harrison_c Posted March 9, 2007 Report Share Posted March 9, 2007 Hi guys, I would like to know how much maximum current is there normally coming from a 12V car outlet, because I want to connect a resistor and LED with a car charger adapter. By the way, how can we measure the maximum current from a power supply if we don't know the current limit? Thank you.Honford Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 9, 2007 Report Share Posted March 9, 2007 A car outlet? You mean a cigarette lighter socket?It must have a fuse that will blow if wires get shorted in a crash. Then the wiring won't catch on fire. The fuse might be about 20A.A car battery can supply hundreds of Amps to the starter motor when the engine oil and mechanics are cold in winter. Most ordinary wires in a car will catch on fire with such a high current. The fuses blow before wires catch on fire.All power supplies have a max current rating. If it is exceeded then some power supplies blow a fuse or shut down. Other power supplies are destroyed if their max current rating is exceeded. Quote Link to comment Share on other sites More sharing options...
harrison_c Posted March 9, 2007 Author Report Share Posted March 9, 2007 So you mean I can't hook up with a regular led and resistor to the 12V outlet (too much current), right?! Then I will use a 9V battery to light up the led. Just for curiosity, my last question was that if I cover up the display on the power supply, can you measure how much maximum current from the power supply? For example, I didn't know how much current from the 12V outlet, can I measure it? Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 9, 2007 Report Share Posted March 9, 2007 The load determines how much current it takes if the power supply can supply that much current.A load that draws 25mA will draw 25mA from a little 12V battery and draw only 25ma from a huge 12V car battery.An ordinary LED with a current-limiting resistor draws only about 25mA. The cigarette lighter socket in a car can supply up to about 20A so up to 800 LEDs can be lighted.If you keep adding loading to the 12V outlet with a current meter showing how much current is used by the loads then when the fuse blows you will know its max current rating. Quote Link to comment Share on other sites More sharing options...
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