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Amperage is measured with an amp meter that is placed in the line that feeds the fuse panel. That means that any load the fuse panel requires must pass through the amp meter. They have been deemed dangerous by some for that very reason and a volt meter is the preferred alternative.

Vince
 

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Discussion Starter · #3 ·
measuring Amperage

Thanks Vince


What I need to know is, once the Ampmeter is set to the correct Amperage , which of the probes are used , is is there one across the main fuse ie posative , neutral either side - across ?

thank you for the assistance


Fahr

Can a votage measurement and a calculation arrive back at Amperage.
 

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Fahr said:
Thanks Vince
What I need to know is, once the Ampmeter is set to the correct Amperage , which of the probes are used , is is there one across the main fuse ie posative , neutral either side - across ?

thank you for the assistance
Fahr.
You must find the main power feed wire to your fuse panel, disconnect it at the source and place the positive amp meter lead where you lifted that wire. Place the negative amp meter lead on the wire you lifted. Now all the current will be flowing through your amp meter.

Warning: make sure the wire size you are using for your amp meter is of sufficient size to handle the anticipated load.
Fahr said:
Can a voltage measurement and a calculation arrive back at Amperage.
You cannot figure amperage with just a voltage measurement you must have one other factor in the formula as follows.


To find voltage, [V = I x R] V(volts) = I (amps) x R(ohms)

To find current, [I = V / R] I(amps) = V (volts) / R(ohms)

To find resistance. [R = V / I] R(ohms) = V (volts) / I(amps)

Vince
 

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Most small hobby "ammeters" measure milliamps, and do not have a scale high enough to use on a car. If you put one inline in the circuit, it will probably fry the ammeter.

Automotive ammeters usually have a shunt arrangement (which has a known resistance) that uses the formulas listed by 302 Z28. The principle is that if you measure the voltage at two points, and have a known resistance between the two points (that is the value of the shunt), the meter can calculate an amperage.

Another option is one of the inductance ammeters, where the meter probes are shaped like two short arcs, and you just surround the wire where you want to measure amperage. They are more expensive meters, but you don't have to disconnect any wires to use them.

Bruce
 

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75gmck25 said:
Another option is one of the inductance ammeters, where the meter probes are shaped like two short arcs, and you just surround the wire where you want to measure amperage. They are more expensive meters, but you don't have to disconnect any wires to use them.
Bruce
In industry those are known as "CT's" (current transducers) and are commonly used on large motors. The CT is placed on the "T" leads of the motor to measure amperage. Three phase motors will typically have one on each phase leg.

Vince
 
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