if I need to measure amperage in the higher ranges..
say up to 60 amps,
I just use an old dash gauge ..
one that reads plus and minus , with zero in the middle ..
like you might run on an old generator car.

sometimes for short finding I might put an automatic circuit breaker in
series with it..
so if a dead short does occur during testing, the automatic circuit breaker
breaks contact and nothing melts or gets damaged.   'Low tech whenever
possible.'
Scott
turbovans

----- Original Message -----
From: "David Beierl" <dbeierl@ATTGLOBAL.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Sunday, August 22, 2010 5:31 PM
Subject: Q&D High-current ammeter

> 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