Electrical losses

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I am trying to find info on electrical losses for resistance welding. Specifically I am interested in finding inductive losses info, what ratio of total electrical losses they represent typically for various cables and geometries. Do inductive losses change in respect to triggering angle of SCR's. How to predict inductivity of electrode/cable/busbar loop. Also for Ohmic losses interested in finding study material for different contact surfaces.

-- Sinisa Jezdic (sjezdic@hotmail.com), November 23, 2001


I am familiar with the resistance of the secondaries, which varies from 100 micro Ohms for a small "transgun" to 800 micro Ohms for a manual gun with a 10 foot kickless cable. Some cable's resistances: 18 inch 1000 MCM = 21 micro Ohm 32 inch 1000 MCM = 33 20 inch 750 MCM = 33 Each side of a 10' kickless 500 MCM is 211 micro Ohm. The transformer has resistance also, and oddly enough has internal voltage losses due to this. A 12 volt transformer may only put out 8 volts under load, at the lugs. Inductive reactance doesn't cause heat loss, but it generally runs about the same magnitude as the resistance values do. The kickless cable is very low inductance compaired to separate jumpers. The weld averages 100 micro Ohms, so you see our losses are about ten times the value of the energy doing the work. Not the most efficient process, but still the cheapest... Weld gun companies are well versed at calculating impedance, they may help. Savair, Milco, Grossel are some in the Detroit area. There is a small difference in inductive effect depending on where the SCR is fired. Generally the sooner you fire it, the longer it takes to reach "drop out" current after voltage zero crossing, for a given inductance. Some automatic power factor patents call this the "drive-coast ratio" Do a patent search on "Pertron" or "Gary A Jones" to find this. If you changed the tap switch then adjusted the firing angle of the SCR to give the same equivalent (RMS) heat, this could change the losses, as one way has higher peak currents, produced by higher peak voltages, the other is lower on both. I haven't thought this through completely, but it feels like there would be additional losses on the high tap.

-- David Bacon (dbacon@updatetechnology.com), April 19, 2002.

About those contact surfaces, most are 3-4 micro Ohms. They can be 1 micro Ohm if silver plated, 10 micro Ohms if they need service.

-- David Bacon (dbacon@updatetechnology.com), April 19, 2002.

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