Lincoln Wirematic 250 problem

You haven't mentioned much about what or how he's welding except that it involves a wire feeder, but if he is using solid steel wire with gas shielding, he could be losing the shield from either an electrical or mechanical problem. That will give a sputtering, bubbly and ugly weld.

You may need to answer a few of the following to get more specific help.

Is it mild steel or aluminum, you are welding? Are you using solid wire, flux core? Are you indoors or out in the wind?

Before you go too far with the hard stuff, check out the obvious. You need a steady flow of shielding gas for welding with solid wire. Too fast of a rate can cause suction of air into the flow. Clean metal helps a lot.

There are others that frequent this newsgroup that can probably be more helpful but I have a couple of suggestions. If you haven't already checked, make sure the gun and the ground cable have firm, clean connections. If not they can easily heat up and cause problems. Also, have you checked that the wire is feeding smoothly? If it's skipping or hanging up in the liner it can cause problems.

Also, if he's using gas make sure he has consistent flow.

Best Regards, Keith Marshall snipped-for-privacy@progressivelogic.com

"Keith Marshall" wrote in news:%4v9b.747$ snipped-for-privacy@twister.southeast.rr.com:

Alex i had the same problem at work the voltage was fine then it would change five volts next time i put down the weld. It turn out to be the scr but how they describe it is one regulate the voltage in and one regulate voltage out. but if the voltage going in is not right it will confuse the voltage going out. example: 32 volts in standered, but actually it is 28 then the output should be 24 but in reality it is 20 volts. I dont know if this helps. im dont work on welding machines but i do know what happen to me.

shipyard worker

Oh, almost forgot , you want to keep the proper distance from the work piece! I added that because you did'nt indicate whether he was an experienced welder! I have both welding and electronics background and most of the machines i,ve worked on usually ends up to be your consumables , tips, liners, wire, etc! And the user! The 2 major component i've have to replace are contactors and diodes! You can usually burnish the contacts inside the contactor!!

sounds simple bit check the welding wire for rust or feed problems doug

Hello everyone...

First of all, I'd like to thank each and every >You may need to answer a few of the following to get more specific help.

We tried both.

Mmmm... I don't know.

Indoors.

Keith Marshall writes:

liner it

From what I could tell, the wire is feeding smoothly. He would know better and I'm sure he'd see it first as he is a proffessional welder.

This suggestion came up a few times. I'm trying to remember whether or not he tried using a different tank. But I will check this next time I'm in his shop.

Shipyard Worker writes:

would

One thing I should mention, and I forgot in my original posting, is that I had my voltmeter sitting on the filter caps. The measured voltage was about the same as the one on the dial. While he was welding, the voltage held up pretty good until the weld started to sputter and burp. I've noticed DC voltage variations and quite an AC ripple (about 6VAC). To me this indicates an excessive current flow or the fact that the microprocessor is firing the SCRs at the wrong time thus not regulating the output voltage properly.

mylo writes:

The contactor is at the back of the unit? Or are you talking about the power switch?

I'm sure he would have noticed it. He is a very experienced welder.

Good idea.

We tried three different rolls.... :(

This suggestion came up a few times... hmmmmm...

Well.. apparently he used another welding machine on the same circuit and it worked fine for him.

OK...let me ask you this: if there was a problem with the gas feed to the gun, would this cause voltage variations and the control board's inability to properly regulate the output voltage? I checked the SCRs using a low power load, they worked fine but I wonder if their behaviour would be different under load? Have you ever seen control board failures?

Once again, thank you all very much for your help. I really appreciate it.

Alex VE3GOP

This sounds to me like you've got either an obstruction in the regulator or the tank valve isn't allowing adequate flow.. it sounds like the shield gas is accumulating in the system but the reg. isn't supplying enough volume, it's not keeping up with the demand. It recovers between attempts to weld and again stores that 5 second amount of gas. This is assuming that you're stopping to look and dial the machine each time it go wacky and then the thing works for a bit again, but I'd say that there's little in the machine and the supply of power that'll give what sounds like the typical case of a lack of shield gas.

Does the machine have a real flowmeter (with a little tube and a ball in it to indicate volume) or is it one that has a gauge to indicate flow? If it's the gauge type you might find that there's an orifice on the inlet, this could do exactly what you're describing.. as could foreign matter in the regulator inlet

John

back of the unit, the contactor should be located right after the voltage selection terminal! At least all the machine i've worked on had a contactor lincoln, linde, ltec and miller! How old is this machine? I did'nt see it on

It took me a few minutes to find the manual, but its on the lincoln web site !!! I've have'nt looked at it yet , but if I come up with something I'll past it on too!!!!!!!!!!!

the schematic, it don't have a contactor it uses scr's to switch power to the work as you already indicated!! At any rate the schematic for the control board is included in the manual!!

the schematic,

It is very unlikely to be a microprocessor problem with those symptoms.

To me it indicates a high resistance developing as some poor connection heats up in the circuitry feeding the filter capacitors. If you have an IR temperature gun, look for hot spots when the welder malfunctions. (If you don't have a noncontact temperature probe, unplug the welder and *immediately* feel around for hot spots when it acts up.)

Likely places to look would be the bolted connections to the SCRs, primary or secondary connections to the transformer, the circuit breaker, etc.

I know you said you checked the filter capacitors, but they could still be at fault. One or more of them could be developing a high ESR as they heat up under full load. But I'm betting on a loose or corroded bolted connection somewhere in the circuit before the capacitors.

Gary

Mylo... there is no relay. All I've seen is a knife type power switch. I did consider cleaning that thing off at one point but if the switch was dirty, I would most likely have problems with the logic +5 volts on the control board. The +5v is solid as a rock...with no ripple. The machine is about 13 years old, you can find the block diagram at

thanks Alex

Hi Doug...

Being an experienced welder, I'm pretty sure he would have noticed feed problems but this sure is worth exploring. We tried three different spools of wire with the same effect.

Alex

John...

if I recall correctly, the weld goes from good to wacky to good to wacky in a rather predictable cycle. During all that, I've been measuring the voltage accross the bank of capacitors and while the weld was good, the voltage measured a steady DC voltage with small amount of AC ripple on it. As soon as the weld begun to screw up, the DC voltage varied all over the map and the AC component was about 6 VAC. To me this indicates poor regulation due to an overcurrent condition or the inability of the control board to regulate the output voltage or even perhaps one of the SCRs going wanky. Both SCRs were bench tested good although I was only able to test them at much lower current. I wonder whether or not the problem with the gas supply might have something to do with voltage regulation but I can't really see why it would. I don't know what sort of a flowmeter this machine has. I took a quick peek at the user's manual at

Alex

Hello Alex, I would like to suggest that you fault find this unit as though it was a normal electronic power supply.

To do that you would connect up a load resistor to the output terminals and monitor the current flowing in the resistor with an ammeter and monitor the DC Voltage across the resistor with an Oscilloscope.

Now you can take all the time you need without worrying about wasting wire and gas as you would have removed the wire and turned the gas off.

From your junk box you could probably find resistors of a few ohms to test the unit with a light load of a few amps. Then parallel your resistors to obtain a load current of several amps. If the intermittent or rhythmic problem does not show up with low current then test with a higher current.

Finding a cheap high current load is going to be a problem. Maybe you could scrounge a few yards of thin stainless steel mig wire from somewhere and wrap it tightly round a house brick. Use some screw tight electrical connections to hold some thick copper insulated cable to the stainless wire and submerge the brick dummy load into a bucket of water.

Maybe you will need a few buckets with brick loads, in series and then in parallel to experiment with different heavy load currents.

With your load current flowing you now have plenty of time to poke, prod, look for hot bad joints and make measurements.

That would be my approach Alex, Regards, John Crighton Sydney

I think you just need the bucket of water as a load resistor. Measure the resistance pure and add salt or baking soda as needed to reduce resistance to the desired experimental level. To get even "fancier", put screws into the bucket sides below water level to use as electrodes! Replace them as needed.

I'd think that if the weld goes wacky it would definitely affect the voltage. During normal welding the wire is shorting to the puddle in a high speed smooth manner. But when loosing shielding gas the weld becomes much rougher with the wire shorting in a unpredictable manner. The welder can only do so much trying to keep the voltage up. At some point it has to drop.

Wayne Cook Shamrock, TX

Good idea Gary. I'll keep that in mind.

SCRs were taken off for testing. Transformer is a likely suspect. Circuit breaker can probably be ruled out as he was using another welding machine on the same circuit. Although the power switch of the welding machine in question might have something to do with it.

The capacitor issue. I had the same feeling. I mean after 13 years of high current operation and they still maintain their original capacitance? We might just change the caps as well as the SCRs on spec. Just because...

But sure enough we will check all the connections...

Thanks Gary!

Alex