Electronic – DC adapter not supplying current

adaptercurrentdc

I'm trying to get .5 A of current from a mobile phone's DC adapter, which is within its rated specifications. I am able to detect a voltage of ~5 V DC between the power and ground wires, so it seems like the adapter's working. However, when I apply a load between the two wires, I can't detect any current flowing with my multimeter (it's set to mA, and the terminals are in the correct sockets). I've tried putting a rheostat in between (from 0-1 megaohms) the two wires, as well as a very fine nichrome (resistance) wire – no current flows in either case. Am I doing something wrong, or does the cell phone charger have some sort of safety mechanism built in that prevents it from supplying current to only the phone?

thanks

Best Answer

As others suggest, you may have done violence to your metre fuse.
MOST meters will blow their mA range fuse if shorted across a power supply.

Connect, say, 47R across 5V supply.
Measure the voltage.
If the voltage is still about 5V, the supply is just about OK.

  • I = V/R
  • I = 5/47 ~= 106 mA.
    Enough for a test.
  • Power = V2/R = 5 x 5 / 47
    -~~ 0.5 wATTS.
    Use 1W

Or use a smaller still resistor to get larger test currents - but 47R should be enough to check.

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