way to measure high amperage

[jeepguy]

i was watching the video of zff's poor mans shunt and was wondering if you check the ohm load and divide that by voltage would that not give you the amperage as well? 

[z.monkey]

Howdy,

When you measure the load with an ohm meter when it is isolated from the circuit you are not going to get the correct reading.  When you put the power to the load it is going to heat up and the resistance will change.  The only to get a correct reading is with an ammeter.  If you don't have an ammeter run the load at full current.  Then shut off the power and very quickly disconnect one of the power supply leads and connect the ohm meter.  This will give you a reading that is closer to true and a lot closer than a cold load.  But really the only way to do it is with an ammeter...

Blessed Be Brothers...

[jeepguy]

would a dc shunt be more accurate than testing the ohm load on a hot circuit

[Jokker]

The simplest ohms law is about whole circuit ( voltage source) so i guess it is way more complicated that simple ohms law. Simple multimeter can help u out. Although u may want to check tutorial how to measure stuff like voltage current ...

[z.monkey]

Howdy Jeepguy,

A shunt is the best way to measure current in a live circuit.  The ammeter is a shunt.  It is a low value resistor across which you can measure a voltage drop.  Then use ohms law to calculate amperage.  You can get the current reading by measuring the voltage drop across the resistor divided by the value of the resistor.  12 volts divided by 0.1 ohms equals 120 amps.  If you use a 1 ohm precision resistor as the shunt the voltage number on your meter literally is the amperage even though the scale says volts.  Automated test systems use ADCs and microcontrollers to measure current readings on many lines when testing electronic equipment.  Say you wanted to measure currents on a 32 bit bus.  You would set up 32 shunts monitored by 32 ADC channels, and the microcontroller would read the 32 ADC channels and record the results.

OK, have fun with that,

Blessed Be Brothers...