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Old 10-23-2012, 11:21 AM
numindast numindast is offline
Properly chastised re: Xi
Location: Chicago
 
Join Date: Apr 2008
Posts: 1,007
Mein Auto: 2005 325xi
Quote:
Originally Posted by klixtokw View Post
not necessarily if you have a meter with the proper current range. I did check for parasitic currents and also checked for the large starting current of 600 a using a hook on meter rated for 1000a.
Just to be clear here: a typical multimeter (digital or analog) can probably handle measuring DC amperage (current) up to a few amps. The fuse inside the meter is to prevent overloading the measurement circuit which can and will blow out the electronics in the meter. Typical multimeters are used to measure current in small quantities like milliamps. To take such a measurement the meter is connected in series to the circuit. Thus this is good for testing parasitic draw, as noted. The moment you fire up anything that can draw more than a few amps, such as power window, power vert top, or headlights, BAM there goes the meter's fuse. Or it goes up in flames.

A clamp-on DC current meter (ammeter) works by sensing the magnetic field surrounding the wire when current flows through it. (Electricity 101: current flowing through a wire induces a magnetic field along the wire. Placing small coils of wire in a magnetic field produces electric current in the coils, which is measured by the meter.) The clamp on meters usually don't do milliamps very well simply because clamp-on ammeters are meant to measure big draws, not little ones. There are many factors including geography and surrounding equipment/electrical that make the clamp-on ammeter more or less useless to measure small amounts of current. Note this is not in the circuit being measured at all, neither parallel nor series. Just don't take a DC ammeter and clamp it around a 1500 volt AC transmission line

Using a clamp-on ammeter, if the current reading does not change when turning the ignition key, then a) the interlocks are preventing the circuit from closing, and/or b) the power is not being delivered to the solenoid/starter. Power delivery can be interrupted by loose wire connections and poor ground straps. At the weak points (loose connections) the temperature would go up significantly due to resistive heating, unless the resistance due to poor connections is so high that hardly any current can flow. (Witness the failed ground connection on E46 taillight assemblies; they melt because of poor connection and underrated connectors.)

I hope this background helps when learning how these tests reveal important clues.
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Quote:
Originally Posted by Fast Bob View Post
...the last thing you need is unpredictable rubber
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