Hi Steve,
Better get new batteries for that multimeter, or else use it as ballast.
No selfrespecting digital multimeter would ever give a reading as high
as 4 ohms with test leads shorted. I just repeated your tests on my test
arrangement here, with these results:
The setup is a Flamethrower II coil with a 0.05 ohm, 1% accuracy power
resistor hooked up in series (that is so I can measure coil current with
a live ignition system running, by recording the voltage across the
resistor when the coil is charging, using an oscilloscope).
Meter with test leads shorted: 0.3 ohms
Meter connected across the 0.05 ohm resistor only: 0.3 ohms
Meter connected across the coil only: 0.9 ohms
Meter connected across a 1 ohm, 5% accuracy resistor (I use these in the
tach modules): 1.2 ohms.
Meter connected across two 1 ohm resistors in parallel: 0.7 ohms.
Meter connected across three 1 ohm resistors in parallel: 0.5 ohms
So here, if we subtract the 0.3 ohm "zero reading" from all these
measurements, we end up with 0.6 ohms for the coil, 0.9 ohms for the
single resistor, 0.4 for the pair in parallel, and 0.2 ohms for the
three-resistor combination. If we assume a 0.1 ohm basic accuracy (since
that is the smallest digit it will tell me), we can see that allowing
for a 0.1 ohm offset, all the numbers come out pretty much exactly as
expected for the known resistances, and the coil then measures at 0.6
ohms, plus or minus 0.1.
Your resistance ratios may still be accurate, but the magnitudes are off
by about one order, and that will also affect the theoretical power
dissipated in the coil and/or resistor by a factor of 10.
Theo
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