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Date:         Sun, 22 Aug 2010 20:31:24 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Q&D High-current ammeter
Content-Type: text/plain; charset="us-ascii"; format=flowed

Here's a link that shows you how to make and use an ammeter shunt. http://www.motorcycleproject.com/motorcycle/text/shunt.html

It should be good for maybe as much as 200 amps for measurements a few seconds long -- if the clips make excellent contact on each end.

Because it's made of copper this shunt is highly temperature-dependent -- for every 10C/18F rise from room temperature the reading will rise by ~4%. But it's cheap and easy and will certainly give you a good ball-park reading. For accuracy I would also add a small wire sticking out of the back end of each clip to attach the meter to. It's the length between attachment points that matters. To slow the temperature rise for high currents you could make it serpentine and clamp it between a couple hefty chunks of aluminum.

To read lower currents you can double the length between measuring points, so that you get two mv per amp instead of one.

Yours, David


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