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Your engine starts and runs. When you try your grinder, it idles up and the grinder runs normally. But she won't weld, or you get what we call a sparkle on the end of the stinger.
When any SA200 or SA 250 welder comes into our shop, it has auxiliary power (it will run a grinder), and the customers tell me, "ran great yesterday, but this morning, no weld. Or it was welding fine, and it died in the middle of a weld. Typically, it is one of two problems.
Check Your Rheostat (They will die of old age.)
`The rheostat knob should move up and down, back and forth, smoothly with no catches.
1. A defective rheostat, also known as the "heat" control. Do a visual check; look for broken wires,
broken white porcelain, and whether the wiper moves freely.
2. Check the resistance with an ohmmeter, lift the wiper arm, and lift it with a piece of paper or
a wooden shim, as shown in the far right image. The two outside terminals should read 64 ohms +/- 10%.
3. Remove the shim and test the resistance between the wiper tab (in the center) and either tab on the side. It should read 0 to 64 ohms smoothly, with no breaks, up and down.
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If money is tight, you can buy a Chinese El Cheapo M5090C from Amazon with this link. You can't use your original Lincoln knob, but it will work. Click on the image to order.
Testing your shunt coils, the Right Way
The procedure that we use in our shop to evaluate a customer's machine. Coming out of the welding stator, you will see five large welding cables that go up to your range switch.
Along with these cables, there will be two or more small wires. They originally were brown and blue.
If you trace them out, one will go to the rheostat, and the other one will go either to the exciter, down in the machine, or to the PCI board. Once you have identified these wires in a location that would be easy to reconnect if necessary.
Strip 1/2 inch of insulation from the two wires going into the stator housing. The resistance reading between the two wires should be 40 ohms plus or minus 10%. (36 to 44 ohms). So many people call and ask about these resistance readings. If you're using a cheap "Harbor Freight" multimeter, don't be surprised if you get a screwy reading. These are two large coils, and they should be checked with an industrial meter. I prefer an analog type meter like a Simpson or a Triplet. Resistance in good coils will even change with temperature. They need to be checked at 60°F or above. Normally, you'll get some type of resistance, or there'll be open infinite resistance. If you're using a digital meter, clip the meter leads on the wire and let them sit for a couple of minutes. The meter will need to saturate the coils to get a proper reading. Check the images below.
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Replacing your shunt coils is a major job, a pain in the ass; you only want to do it once.
1. Have a reputable shop for the job. Make sure you get a warranty, in writing, and pay for it with a credit card. It gives you leverage in a dispute.
If you have any doubts about the shop that will work on your stator, ask questions.
1. Ask them how they remove and replace the shunt coils? If they say they pound them out and pound them back in, go somewhere else.
Here at Weld-Mart, we have a specific procedure for removing and replacing shunt coils. First, we clean all the dirt, oil, and crap out of the stator housing. Before we do all the coils to make sure there's nothing shorted to ground. People ask me whether I check the coils' resistance. The answer is no. Their resistance is so low that you really can't tell anything. And replace any defective cables and fix any problems we can't identify. We remove and replace the defective shunt coils. The housing is then dried out and rechecked with a high-voltage tester to ensure there's nothing going to ground. We coat the whole interior of the stator housing with an industrial red epoxy. We have never had a warranty claim on any of our shunt coil installations. The warranty is lifetime for the original purchasers.
2. Remove the stator housing yourself, take it to a motor shop that can R &*R the shunt coils. You need the experience of servicing your machine. If you buy your shunt coils from us, we will provide you with unlimited telephone support. Check around, nobody seems to know anything today. I call it the "Age of Incompetence". I recommend that all my customers get as comfortable with their machine as they are with their wife, girlfriend, or favorite goat!
Please call or email us for more details
Suppose you do not have a motor shop close. Pull the stator housing, bolt it onto a pallet, and ship it to us. We will evaluate the item, repair any necessary issues, clean and dry it out, and coat it with epoxy if we install Weldmart coils. This installation comes with a lifetime guarantee against defects in materials and installation. We have been installing and selling our coils for over thirty years, with no known failures.
The image above is of obsolete Lincoln OEM shunt coils. The coils were wound on a sheet metal form insulated with paper.
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