A way to test high currents ?!

[edy252]

hi all....

i've been thinking about how to read high currents (25 to 50 amps)....i thought of seperating the input wire into a certain number of wires in parallel (3 wires for example)...then adding an ammeter to one wire....then multiplying the given amperes by this number (3 in this case) to get the total amps....

would this work? (i'm asking because i dont have a big ammeter.....& i'd save some money if i dont buy a big one !!! )

[troy]

Is the current AC or dc?  If AC, there are lots of clamp on digital ampmeters that are both cheap and effective.  Harbor Freight is where I got mine.  The deluxe model was on sale just over 30 bucks.  The basic model often goes on sale for around 15 bucks.  Both model will measure current into the 100's of amps range, IF it's AC.  Also note that the clamp must only go around one of the two wires supplying the current to the load.

Otherwise, your method should give decent approximate results IF your amp meter doesn't introduce much resistance in the isolated wire, AND each wire is identical in gauge, length and temperature.

Good luck and have fun.

troy

[edy252]

hi...and thanks for ur reply...

but i'm asking about dc....it was just a thought depending on the rule that intensity is divided into equal 'amounts' in identical parallel branches....

[Victor]

Dividing the current will not be acurate because

A)  The connections will probably have different  resistances and

B) because the ameter introduces a resistance of it's own

 These two things will cause the currents to be uneven in the wires

 You can Buy a fifty amp shunt pretty cheaply and measure the millivolts across

it.

 OR you can use a piece of # 8 wire for a shunt . A length of I think 21 inches is 1 milliohm and will drop 1 millivolt per ampere . you will need to check on the length. Using 10 gage 1 foot  = 1 milliohm, fifty amps would be pushing #10 though.  The reading will drift with the temp of the wire, but  it is not to much of a problem.

Victor

[Opera House]

You can use a piece of copper wire, 625 feet of #12 copper is one ohm. Figure out a distance for say 100 mv for X amount of current. Problem is as the wire heats up, the resistance changes. I have built a lot of wire shunts for analog meters by making the wire a little bit longer and putting a resistor in series with the meter. I use a load of lamps and adjustable power supply to get a known current of 5A to 10A to calibrate the shunt for a higher value.