Measuring DC Arc Welder AMPS

I am doubtful of the Amp slide indicator accuracy on my 110 VAC welder that I converted to DC.
It is a Merlin 150BC and the indicator goes up to 150 AMPs.

I use 3/32 6011, 6013, and 7014 rods and they will burn from about 60 to 150 AMPS 'Indicated".
(BTW - I cut almost the entire rear panel open and attached a cooling fan and it does a god job of burning rod after rod. I plug it into a 110 VAC 40 amp receptacle.)
How does one measure the DC arc current?
Is it the same as the shorted rod current?
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"BoyntonStu" (clip) How does one measure the DC arc current? Is it the same as the shorted rod current? ^^^^^^^^^^^^^^^^ You need a BIG ammeter. The short circuit current will be a little higher than the arc current. In college lab, we use a millivolt meter and shunt to measure high currents.
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Leo Lichtman wrote:

Or a hall-effect sensor.
Steve
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BoyntonStu wrote:

You need a clamp-on type DC current probe with averaging and digital readout. Note, most clamp-on current probes are for AC current and they will give incorrect readings. Once you have the correct tool, then it's easy - clamp the meter over one of the welding leads (either electrode lead or ground lead, doesn't matter) and have someone read the meter while you run a bead.
Maybe you can borrow or rent one. You might ask a staff member at your local technical college's welding school, those guys often have one, or maybe a guy who works at a welder repair shop.
GWE
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Grant Erwin wrote:

You could measure primary current and scale it back through the transformer to secondary current ? Its probably closer than the knob on the equipment ! Steve
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"Grant Erwin" You need a clamp-on type DC current probe (clip) ^^^^^^^^^^^^^^^^ Good one, Grant. I read your entire post, looking for the punch line--didn't find it. Since clamp-on ammeters are basically transformers, the work on AC only.
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Leo Lichtman wrote:

No, there are clamp ons for DC too, they use hall-effect sensors and can read both AC and DC.
Steve
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On Fri, 11 Nov 2005 21:27:21 +0000, the renowned Steve

Yes. I've got these on eBay, but have never tried them on a welder:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&itemu62347255
You get the idea. Because of the Hall sensor, they power up with an offset that needs to be nulled by pushing the orange button.
Best regards, Spehro Pefhany
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Spehro Pefhany wrote:

Hi Spehro,
Often been tempted, but never really been able to justify it. Ah well. Steve
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^^^^^^^^^^^^^^^ When did they come out with that? Next, you'll be telling me they have light emitting diodes, flat screen TVs and digital phonograph records. :-)
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http://www.hotektech.com/GMCMetraclip70.htm
Digital Display 7 segment characters, 4 digits Sampling Rate 500 ms Direct and Alternating Current, A DC and A ACeff Direct and Alternating Voltage, V DC and V ACeff Frequency range 45 Hz ... 450 Hz Input impedance 10 MOhm Resistance Measurement Maximum open-circuit voltage 0.5 V Maximum short-circuit current 0.37 mA Frequency
http://www.swainmeter.com/pl.html
Real ammeters -- both AC and DC -- are now available in non-contact or clamp-on form. These Sea Clips and Sea Clamps? measure the actual CP current in a line at the spot where you put them. In one form or another, they measure 5 milliamperes to 500 amperes in conductors from inch to 5 feet in diameter. Resolution of 1 milliampere DC (0.1 mA AC) can be provided from " to 30" diameter with sensitivity accuracy typically 1% of reading. Adjacent conductor interference and zero offset error due to residual local magnetism are reduced by new technology.
Five figures are presented to illustrate the use of these ammeters. Specific data refers to the ammeters I know best: DC and AC Amp Clips and Clamps manufactured by the William H. Swain Co. under the marks Sea Clip, Sea Clamp, and MER? -- the new Magnetic Error Reduction form for improving accuracy.
wrote:

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Leo Lichtman wrote:

Don't tell that to Fluke
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"cl" wrote: Don't tell that to Fluke ^^^^^^^^^^^^^^ I learn something new every day. Does Fluke make a clamp-on plug-in attachment for their digital meters, like their temperature probe attachment?
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Leo Lichtman wrote:

Yes, they do or did. I have a Y8100 that does 0-20A or 0-200A AC or DC. It's pretty temperature sensitive and has to be re-zero'ed periodically with a thumb wheel pot on the handle. I bought it at a surplus sale about 15 years ago. I am not sure whether it's Hall effect or the differential saturation setup that someone else described.
Bob
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There may be clamp on DC ampmeters that use hall effect sensors, but there are also some that are more like transformers. As I remember they are call transductors.
The way they work is by having two square loop cores and an AC supply that drives the windings on the two cores. On one half cycle the AC current aids the DC current on say core A. And core A saturates and does not have any effect on the AC current. But on Core B the currents oppose each other. So now the DC current causes the AC current to be in proportion to the DC current. On the next half cycle it is core A that controls the AC current. So the AC current is alway proportional to the DC current, and you just measure the AC current.
Dan
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I'd just hook my clamp on amp meter on the output of the transformer in front of the diodes. Diodes won't drop the current any, only voltage. Meter goes to 600 amps so that shouldn't be a problem. Not sure what it does with the crazy phase angle at that point.
BoyntonStu wrote:

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That should work OK. I don't think there is any problem due to any phase angle since the meter is measuring current and cares less about what the corresponding voltage is.
It would be interesting to compare the readings at the transformer and after the diodes. The diodes don't affect the current but the waveform is now different. The average value of the after-diode waveform has a value whereas in the transformer location it was zero (cancelled by the equal positive and negative current values over 1 cycle). One might suspect the rms value which is the heating equivalent to a DC circuit would be the same since the bottom half of the waveform has just been folded up to mesh between the peaks of the top half. Problem is that most analog ammeters are calibrated for a specific waveform (usually sinewave) and are inaccurate for others. Need a true-rms meter.
How important is this in the real world? I just adjust the lever until I get a good weld and I don't care whether or not is 91.000 amps or 94.532 amps as long as the scale gets me in the ballpark. In fact my scale has been fudged by me to have marks for 3/32 6013, 1/8 7014, etc. To put my comment in perspective I should add that I am a hobbyist welder who does everything with mild steel. billh

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BoyntonStu wrote:

I've used battery powered clamp on attachments (yes for DC)that are intended for DVMs and give a fixed output typically 1mv/amp. I have also used shunts and hall effect transducers (CR Magnetics). All worked equally well. In a pinch you could measure the voltage drop across a long length of known resistance wire.
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