3 ms·

> It should be fine with the car not "on" No. Not if the meter is in "Ammeter" mode (or is purely an ammeter only). An ammeter presents a very low resistance

by pwg 4y ago

> It should be fine with the car not "on" No. Not if the meter is in "Ammeter" mode (or is purely an ammeter only). An ammeter presents a very low resistance to the circuit you are attaching it to, low enough that for almost all circuits, it is effectively a "short". If one connects an ammeter across a low resistance voltage source (i.e., across the car battery) the ammeter will appear as a short circuit to the battery, and one or more bad things will happen. The 'least bad' will be blowing a rather expensive fuse in the ammeter that protects it from this kind of accidental use. Several of the "most bad" will involve hot molten metal and/or extreme heat.

mlyle 4y ago
> If one connects an ammeter across a low resistance voltage source (i.e., across the car battery) the ammeter will appear as a short circuit to the battery Yes. My first comment on this thread says not to do that, and suggesting an alternative is "Ammeter between a battery's terminal and the car's electrical system." instead. https://news.ycombinator.com/item?id=35514652 https://news.ycombinator.com/item?id=35514652 I was replying to "anywhere near large enough capacity" in the next post. The typical 10A range is massive overkill for typical parasitic loads in a car, and even things like the fuel pump deciding to kick on and run in most cars.
- johnwalkr 4y ago
  Using an ammeter as you describe would work fine, but the topics this thread including mine should come with a footnote[1] at least. Especially when this thread shows a simple mistake can cause a lot of confusion about what to do. My thought process with my comment about capacity was that muscle memory makes it likely you'll eventually start the car if you're touching the ignition switch/button during troubleshooting, although on further thought and reading the other comments I'd do the following: pull the starter fuse, then use a 10A ammeter function of a common multimeter, connected inline between the negative harness and the negative terminal and not on the positive side.[1] [1]This is just what I would do. Only do this based on a reputable guide if you don't have experience working around car batteries.

by pwg 4y ago

mlyle 4y ago

> If one connects an ammeter across a low resistance voltage source (i.e., across the car battery) the ammeter will appear as a short circuit to the battery Yes. My first comment on this thread says not to do that, and suggesting an alternative is "Ammeter between a battery's terminal and the car's electrical system." instead. https://news.ycombinator.com/item?id=35514652 https://news.ycombinator.com/item?id=35514652 I was replying to "anywhere near large enough capacity" in the next post. The typical 10A range is massive overkill for typical parasitic loads in a car, and even things like the fuel pump deciding to kick on and run in most cars.

johnwalkr 4y ago
Using an ammeter as you describe would work fine, but the topics this thread including mine should come with a footnote[1] at least. Especially when this thread shows a simple mistake can cause a lot of confusion about what to do. My thought process with my comment about capacity was that muscle memory makes it likely you'll eventually start the car if you're touching the ignition switch/button during troubleshooting, although on further thought and reading the other comments I'd do the following: pull the starter fuse, then use a 10A ammeter function of a common multimeter, connected inline between the negative harness and the negative terminal and not on the positive side.[1] [1]This is just what I would do. Only do this based on a reputable guide if you don't have experience working around car batteries.