Re: Ammeters vs Voltmeters ???

Posted by jdemaris on December 12, 2004 at 19:09:32 from (209.23.31.233):

In Reply to: Re: Ammeters vs Voltmeters ??? posted by Rod (NH) on December 12, 2004 at 07:40:43:

The "guru" mentioned in the article you linked to, makes a few errors. First of all, an ammeter does NOT have to carry full charge current - he is absolutely wrong. It is a common practice, especially in automobiles, to use shunt-ammeters. This type of ammeter measures votage drop across a small shunt bar and is hooked with small wires that do NOT carry high current.
Further, for him to state "there is no chance for misinterpreting a voltmeter's readings as can happen with an ammeter" is a little silly. Anything can be misinterpreted, nothing is foolproof, and there are definite advantages and disadvantages to both instruments. That's why I like having both. A voltmeter will not instantly tell you there is an exceptionally high draw on the electrical system when the engine is not running; a ammeter will - e.g. like leaving the lights on by accident. A voltmeter will not tell you your overloaded system is at a discharge every time the engine is idled down like an ammeter will - unless you have a VERY accurate voltmeter and a small battery. Most automotive voltmeters are somewhat vague and most batteries are large enough so they act a buffers to fast readings. On the other hand, a voltmeter is nice since it will report battery condition before the engine is running which an ammeter will not. But, even this can be misleading since, if there is a draw on the system, the volt reading might be an indicator of some other problem like excess current draw - which an ammeter would tell you right away.

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