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Date:         Sun, 11 Nov 2007 15:17:18 -0800
Reply-To:     Michael Elliott <camping.elliott@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Michael Elliott <camping.elliott@GMAIL.COM>
Subject:      Re: Electrical Glitch causiing a dead Aux battery...more..
Comments: To: Don Hanson <dhanson@GORGE.NET>
In-Reply-To:  <001001c824b2$2a1d48c0$68b2d8d1@laptop>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 11/11/2007 2:28 PM Don Hanson wrote:

> Why the hell does a multimeter even have a fuse, any > how?

Great question! Simply put, your basic multimeter is a voltmeter. In order to measure current, a small resistance is typically placed in series with the current flow and the voltage that the current develops across that resistor is read on the meter. For example, a 1 ohm resistor will develop 1 volt across it when 1 amp is flowing through it. But anyway, the resistors can only handle so much current without frying so a fuse is put inline to keep from smoking the resistive bits. If the resistor was made into a high value to limit current the current measurement would be inaccurate. So low resistance for accuracy, which means high current is possible, which means that smoke can happen. Smoke is evil, so we fuse.

When using the meter as a voltmeter, you switch it into high-resistance mode so there is almost no current flowing through it because we don't want to disturb any currents or voltages, just measure the existing voltages. In this case no fusing is needed.

There. An answer that only someone who already knows electricity could understand, while leaving those who don't still in the dark. My work is done. (Dusts off hands and walks casually out of the room, whistling tunelessly.)

Most of my meters have blown fuses. Usually some awkwardly odd size that can never be found locally.

-- Mike "Rocket J Squirrel" Elliott 71 Type 2: the Wonderbus 84 Westfalia: Mellow Yellow ("The Electrical Banana") 74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano KG6RCR


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