[Healeys] Multimeter Question

[Bob Spidell]

re: "... What is going on here?  Why is the meter behaving this way?"

I'll take a SWAG (worth what you paid for it): Measuring DC current is 
more difficult than measuring AC current, which is usually done with an 
inductive pickup. Because DC doesn't create inductance--except 
initially--it usually has to be measured inline; i.e. you have to break 
the circuit and insert the leads between ends. I suspect the DVM passes 
the current through a known-sized resistor, and measures voltage drop. 
The DVMs I've seen/used can only measure a few milliamps, anything more 
/could/ cause the meter to go bonkers, and just a few milliamps would 
take more than a couple days to drain a fully-charged starting battery 
(my Mustang has electrical stuff running even when 'off,' and I've gone 
several weeks without a dead battery). Again, just a guess.

Bob


On 2/12/2021 4:52 AM, jim via Healeys wrote:
> not helping on meter question, but 12 volt lights with clip-leads 
> attached will show current flow quite nicely....remove fuse...clip 
> light bulb across removed fuse...if circuit is conducting current, the 
> light bulb will "glow"    (simetimes called a "bug-lite" by the old 
> Telephone Company Central-Office-Techs)
>
>
> Jim
>
> On Wednesday, February 10, 2021, 4:04:57 PM PST, llennep--- via 
> Healeys <healeys at autox.team.net> wrote:
>
>
> Hello Listers,
> I am seeking to tap the knowledge of the list on this general auto matter.
> I bought a hot rod last year and from the get go I have had a battery 
> drain.  If system is left on the batt will get too weak to start 
> engine in a couple days or so.  Recently I have been chasing the 
> problem in earnest.  I did find one issue and resolved that with the 
> hope that the drain was fixed. No.  Still there.
> So yesterday I began preparing for the standard search method - 
> pulling fuses one at a time and noting the drop in amps running 
> through the system.  However I needed a dependable multimeter.  I have 
> 3 but do not trust the amperage reading on any of them.  I secured a 
> known good meter today and here is what I am observing.
> The reading starts out reading a few tenths amp fluctuating wildly and 
> then drops to almost 0 in 2-3 seconds.  This happens time after time. 
>  What is going on here?  Why is the meter behaving this way?
> Any help much appreciated.
> Keith
>

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