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^ measuring volts in 'series' is meaningless. The input impedance of the meter is typically in megohms and swamps any small 'resistance' it is in series with.
For grins I took a 100 ohm resistor in series with the one of my meters (set to voltage) and saw 12V (exactly what the power supply was set to). 100 ohm and 12V means about 120mA current. I then took a 1k resistor and replaced the 100 ohms and still measured 12V. 1k would be 12mA. This is what I know would occur, but not one to at do a bench test.
So, your method would show no difference between 12mA leakage current or 120mA leakage current. I could have put a 10ohm resistor in series and still seen 12V. Again, the meter's impedance is so high that essentially only uA flow, whether in series with 10 ohm, 100 ohm or 1k ohm.
10ohm would cause 1.2A to flow if it was across the battery - that's pretty high parasitic draw and your method would not be able to identify it being any different that 12mA with 1k ohms.
And this all goes to hell when it's not a pure resistance as the parasitic issue, but instead some active electronics that is misbehaving - which is most likely in our vehicles. With a meter on amps in series with the battery feed, your electronics is actually powering up completely and what you are then measuring is the true current flowing and you can decide if it is a problem or not. With a voltmeter in series you have no idea what the measurement is telling you - is it good, is it bad?
It's real simple. Measure current. Of course the meter in your picture doesn't have that capability... But do note your meter says High Impedance
I prefer using a DC clamp meter (that can resolve mA), it allows me to take measurements without have to undo cables/lugs/connectors. As long as I can put the clamp around the cable of interest I'm good to go.
If you don't have a meter that can measure amps, at least purchase a high power resistor (1 ohm and say 5W) and then you can use it as a shunt and measure the voltage across it. Measure 1V across it and you have 1A flowing through that 1 ohm resistor. Obviously this is for find parasitic levels of leakage current, not measuring high currents. You could use a 0.1ohm resistor and then just multiply your volt reading by 10 to get the amps flowing. etc etc.
The shunt resistance will of course cause a voltage drop (burden), so keep the resistor value low. Multimeters that have current measuring capability will have an internal shunt resistor that the meter measures the voltage across and does the math for you to display amps, mA etc. DC clamp meters are nice since they don't introduce a series resistance to your measurement and you can find models that can handle 100's of Amp.
I = V / R (amps = volts / ohms)
cheers,
george.
For grins I took a 100 ohm resistor in series with the one of my meters (set to voltage) and saw 12V (exactly what the power supply was set to). 100 ohm and 12V means about 120mA current. I then took a 1k resistor and replaced the 100 ohms and still measured 12V. 1k would be 12mA. This is what I know would occur, but not one to at do a bench test.
So, your method would show no difference between 12mA leakage current or 120mA leakage current. I could have put a 10ohm resistor in series and still seen 12V. Again, the meter's impedance is so high that essentially only uA flow, whether in series with 10 ohm, 100 ohm or 1k ohm.
10ohm would cause 1.2A to flow if it was across the battery - that's pretty high parasitic draw and your method would not be able to identify it being any different that 12mA with 1k ohms.
And this all goes to hell when it's not a pure resistance as the parasitic issue, but instead some active electronics that is misbehaving - which is most likely in our vehicles. With a meter on amps in series with the battery feed, your electronics is actually powering up completely and what you are then measuring is the true current flowing and you can decide if it is a problem or not. With a voltmeter in series you have no idea what the measurement is telling you - is it good, is it bad?
It's real simple. Measure current. Of course the meter in your picture doesn't have that capability... But do note your meter says High Impedance
I prefer using a DC clamp meter (that can resolve mA), it allows me to take measurements without have to undo cables/lugs/connectors. As long as I can put the clamp around the cable of interest I'm good to go.
If you don't have a meter that can measure amps, at least purchase a high power resistor (1 ohm and say 5W) and then you can use it as a shunt and measure the voltage across it. Measure 1V across it and you have 1A flowing through that 1 ohm resistor. Obviously this is for find parasitic levels of leakage current, not measuring high currents. You could use a 0.1ohm resistor and then just multiply your volt reading by 10 to get the amps flowing. etc etc.
The shunt resistance will of course cause a voltage drop (burden), so keep the resistor value low. Multimeters that have current measuring capability will have an internal shunt resistor that the meter measures the voltage across and does the math for you to display amps, mA etc. DC clamp meters are nice since they don't introduce a series resistance to your measurement and you can find models that can handle 100's of Amp.
I = V / R (amps = volts / ohms)
cheers,
george.
