can somebody teach me how to measure the output current by correct method?
why cannot use the multimeter to measure the output current directly?
is need to place a shunt resistor by series method then measure it??

 

Multimeters have an incredibly high input impedance. If you connect your meter directly to the output of your circuit and ground you will be loading your circuit with this high impedance. If you put a shunt resitor on the output and measure the volt drop across that resistor then by ohms law you can calculate the output current.

hope it helps

Andy

 

well..the multimeter has current metering mode. but the OP should have posted more details

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Gods own Country
Incredible !ndia

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"Give a man a fish, and he will eat for a day. Teach that man to fish, and he will eat for a lifetime."

 

so, how do i place the multimeter? the multimeter is place at front or after the shunt resistor? & y i need to place tat thx ~~

 

Since you have to ask this question i assume your a beginner.

Voltage is measured in parallel

Current is measured in series.

To measure the volt drop place the probes acros either end of the resistor, taking care to get the polarity right or you will get a negative answer.

You may want to buy a book for beginners which illustrates all the basics, i believe there are lots of tutorials on the internet if you do a search on google.

Hope it helps, others may be able to give you their experiences.

Andy

 

current is measured in series . put the multimeter in current measurement mode , and connect it in series .

if yoy have a voltmeter instead of multimeter , use a low value (ref : the power dissipation in the resistor) shunt resistor and measure the voltage ACROSS the shunt resistor

__________________
Gods own Country
Incredible !ndia

www.flickr.com/photos/_akg/

"Give a man a fish, and he will eat for a day. Teach that man to fish, and he will eat for a lifetime."

 

The multimeter already has a shunt resistor inside. If the meter is used to measure current with it then an additional shunt resistor is not required.

__________________
Uncle $crooge

 

Remember if your going to use this method make sure you select the correct range (200mA or 10A) for your application. If you dont know what currents are flowing use the 10A as a safety net.

Ive blown a fair few fuses in my time but my meter still lives....just

Andy

 

been there... I keep an el-cheapo dmm for just this purpose. Last time I blew a fuse, it was 4 day wait to get a replacement.

 

so,if i wan to measure the mobile phone (nokia, label 3.7VDC 350mA) charger's output current & voltage, how can i measure it??
my lecturer always teach me to measure the current , must place the resistor front of the multimeter by series method, is it correct method??

 

that is one way to do it. the other is place the DMM (set to amp mode) in series with the battery charger to measure current.

 

y i measure the output current and the voltage of cell phone charger is 600mA and 9V, but the charger label it is 3.7V and 350mA, y like this??

 

You should measure the voltage with the charger powering the phone. The voltage will read too high without a load.

You should measure the current of the charger connected to the phone when the phone is turned on. You probably just shorted the charger with the ammeter.

If you connected everything correctly, then your meters are very wrong.

__________________
Uncle $crooge

 

so, if i wan to design a cell phone charger connected by DC power ( for example connected by solar panel ), wat output current & voltage i suitable to use under the no load charger( cell phone no connect to charger)??

 

it depends...
on battery type, on battery capacity, on charge time you want.
it depends on how much of the charing chircuit is in the phone.
it depends if there is temperature sensor