Measuring output current of a switching power supply ?

Hi,
I'm trying to measure output current of a switching power supply.
input voltage is 220 ac.
output voltage is 22 dc.
the load that is connected to the switching power supply has a resistance about 10 Ohms.
I use a 0.22 ohm resistor for converting the current into voltage and then i measure the voltage and convert it into current.
theorically my output current should be about 2.2 amp, it means that the voltage on 0.22 ohm resistor should be around 0.484 volt.
but when i measure the voltage on the 0.22 ohm resistor i measure more that 0.85 volt on it that it means my output current would be more than 3.5 ampere.
Does anyone know why this happens ?
My circuit is attached.

Whats the voltage across the 10 ohm resistor?

If there is no current limiting on the power supply, it will deliver too much current until is catches fire or blows its fuse. Fuses normally blow at three times their marked value in 10 seconds or so, hopefully before it catches fire.
Frank

Low cost SMPS don't have any current limiting mechanism.Current is incresed until transformer and primary side driving circuit is saturated..
Primary side switching transistor is normally selected so that it can handle more than available current but .. not sure.
It's dangerous..

chuckey said:

If there is no current limiting on the power supply, it will deliver too much current until is catches fire or blows its fuse. Fuses normally blow at three times their marked value in 10 seconds or so, hopefully before it catches fire.
Frank

Click to expand...

exactly... one of the capacitors of the power supply where totally damaged after my rest. and one of the resistors was burned completely.
but how i can find that does it have current limiting or not ?
thanks...

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BigBoss said:

Low cost SMPS don't have any current limiting mechanism.Current is incresed until transformer and primary side driving circuit is saturated..
Primary side switching transistor is normally selected so that it can handle more than available current but .. not sure.
It's dangerous..

Click to expand...

How can i find that does it have current limiting or not ?

Is this an off-the-shelf supply? If so, it seems the data sheet would spell out the limits of over current protection.

bking said:

Is this an off-the-shelf supply? If so, it seems the data sheet would spell out the limits of over current protection.

Click to expand...

I think I can use a current sensor for solving this problem to isolate the power supply ground from my microcoltroller ground. Is that correct ?

Its all ohms law,
if you are not getting the expected readings, then
-either the output voltage is not 22 volt
-or the load is not 10 ohm
-or the sampling resistor is not 0.22 ohm