On Sat, 29 Mar 2008 08:55:50 -0700, Gunner
wrote:

On Sat, 29 Mar 2008 08:18:49 -0500, "Pete C."
wrote:


Bob Engelhardt wrote:

Gunner wrote:
Unless you have a DC amp clamp..you cant do it. Most ammeters using
inductince to read current, are AC only. ...

My Fluke does DC amps. Has a "Max" mode too, where it remembers the max
current - you wouldn't need a helper to read the meter while you're welding.

Bob

I found a rather nice hall effect AC/DC clamp probe by TPI at FRy's for
about $60 (plug into any DMM), and it's rated for 1,600A AC / 2,000A DC.
A whole lot cheaper than the Fluke equivalent and seems to work just
fine.


Really? Fry's Electronics
Big box store to the nerds?

Ill check there myself. Id like to have one.
Gunner

You could make one for well under 10 bux. You'd need to calibrate it.
Might not be quite as accurate as a commercial instrument, though most
DC amp clamps aren't all that accurate either. Ya don't usually need
to know welding current to 1%. 5% or even 10% is probably often
close enough.

Some minor metalworking required, and you'd need to stick 3 or 4
electronic parts together.

The clamp ring could easily be tailored to have a max range of 200
amps, 500 amps or 1000 amps just by changing the width of an air gap.

Linear Hall sensors are available for $1.26 from Digi-Key.
http://search.digikey.com/scripts/Dk...me=620-1020-ND
A Hall sensor produces a voltage proportional to a magnetic field,
which in turn is proportional to current flowing thru a wire that is
encircled with an iron or steel structure. The steel structure might
be an openable (hinged) ring maybe 1" ID and 2" OD (or whatever) with
an air gap. The hall sensor goes in the air gap, perhaps surrounded
with aluminum, brass, plastic or epoxy so the air gap is the same
every time. Turns out the permeability of the iron or steel really
doesn't matter much at all, and since you're interested in DC it
wouldn't need to be laminations. Solid mild (soft) steel or iron
should work fine.

The elex parts might be the little Hall sensor, a 5-volt regulator
as LM78L05 (about 40 cents), a small cap and a 9-volt battery. You'd
measure the output voltage with an ordinary DVM.

On the other hand, time is money and 60 bux ain't much of it.