Its not that its "not supposed" to be a load to be tested across.
Any circuit with current flowing in it has voltage dropped across every component of the circuit. And knowing that no good, 8mm section of any circuit in a typical vehicle with less than 50mA running through should ever have more than .0008V on it is actually useful information. So if youve got a vehicle fully powered down and youve got a fuse thats dropping a millivolt(.001V) or more you can be pretty sure theres significant current flowing in that circuit to kill the battery prematurely.
The issue is that with the small sections of circuit, small currents, and even smaller voltages we are dealing with, any inaccuracies in your meter(lots of guys use cheap *** DMMs)any imperfections at the measuring point due to corrosion or other poor contact issues dramatically skews the results.
Its still useful test, its just(like anything)that you need to fully understand what youre measuring and what it means. If your ammeter reads that youve got 35mA to hunt down....youre not gonna find it by voltage drop testing across fuses, however if your ammeter is broken or otherwise unavailable or is attached to a Counselor cart that isnt convenient to roll outside then you can make some quick useful measurements with a high quality resolution DC voltmeter. If youve got 1mV across a circuit you can be pretty confident theres at least 50mA flowing in that circuit.
Any circuit with current flowing in it has voltage dropped across every component of the circuit. And knowing that no good, 8mm section of any circuit in a typical vehicle with less than 50mA running through should ever have more than .0008V on it is actually useful information. So if youve got a vehicle fully powered down and youve got a fuse thats dropping a millivolt(.001V) or more you can be pretty sure theres significant current flowing in that circuit to kill the battery prematurely.
The issue is that with the small sections of circuit, small currents, and even smaller voltages we are dealing with, any inaccuracies in your meter(lots of guys use cheap *** DMMs)any imperfections at the measuring point due to corrosion or other poor contact issues dramatically skews the results.
Its still useful test, its just(like anything)that you need to fully understand what youre measuring and what it means. If your ammeter reads that youve got 35mA to hunt down....youre not gonna find it by voltage drop testing across fuses, however if your ammeter is broken or otherwise unavailable or is attached to a Counselor cart that isnt convenient to roll outside then you can make some quick useful measurements with a high quality resolution DC voltmeter. If youve got 1mV across a circuit you can be pretty confident theres at least 50mA flowing in that circuit.
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