Relay or circut board

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I have a century 225amp mig welder.  It worked fine and then I loaned it to a friend for a project and now it does not work.  The fan turns on the gun works (wire feeds) and the gas works.  But I can not get it to arc.  I have taken apart the ground wires and they were clean and tight.  The owners manual states that the Triac realy and or the circuit board needs to be replace.  Both are about 150 to 175.  Does anyone know if there a way to test the relay?  I have not been able to find anything on the web as of yet.  I figured I would ask the experts while I continue looking.ThanksBRB
Reply:I would check the connection at the plug for the gun.  Whatever your friend did to it was probly something simple.  Of course, if your machine has tapped volt settings and he turned the knob while welding, he may have fried something in the machine.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:What model welder?  Can you get a schematic for it?  Who makes Century?Is the "relay" or triac used just for on/off switching of the welding current or is it used for phase control, i.e., to dynamically control the power delivered?At that price, I'd want to be sure I knew which part failed (and, if possible, why) before investing in a replacement part.  Testing is feasible, possibly even easy, but advising on how would be MUCH easier if we could see a schematic diagram of the welder.If getting a schematic is impossible, at least detailed, clear photos of the interior of the welder (often a rat's nest), the relay/triac and its wiring, and the circuit board would help a lot.Have you done a careful, close-up inspection of the guts of the welder to look for overheated, melted parts?  can you smell any odors indicative of overheating?  Sometimes a really close examination with a magnifying glass reveals burned components.If it is a transformer welder, measure the windings for continuity, end-to-end and shorts to ground.  It's probably not worth trying to repair a welder with an open or shorted transformer winding.  That's not likely to be your problem, but it's worth eliminating as a possible problem before spending a lot of time or money.Can you see any manufacturer's part numbers on the triac or relay?  Does it look like a transistor or a potted box?  If it is used simply as a "static switch" (i.e., an on/off switch) it can probably be replaced or substituted for fairly cheaply and easily.  If it is used as a phase controller (dynamic power control) things get trickier.  But I suspect it is simply a static switch.awright
Reply:awrightThanks for the guidance.  I am working on getting the schematics reduced so I can scan them into a file.  I have some pictures but they are not very clear.  I don’t know if it is any help but the relay has 2 wires in and two out.  The wires coming in are   1- is from the transformer and the other 2- is from the power switch.   The two wires on the out side of the relay are 3- goes to a rectifier & circuit breaker and the 4- wire goes to the control circuit board.  I am working on getting a copy of the schematic and some pictures for you. Thanks for the assistanceBRBIntegrity is doing the right thing when no one is looking!
Reply:Lets give this a try.  here a two pictures of the relay.  I should have schematic reduced so I can scan in by Thursday Attached ImagesIntegrity is doing the right thing when no one is looking!
Reply:OK.  That's a lot of informatio, but the photos could be a bit better by more clearly showing the ratings and the model number.  It is clearly a static switch.  That is, it is either on or off.  It is not a variable output phase control device.  Crydom is a major manufacturer of SSRs (Solid State Relays) like this.  Can you confirm that it is a model 2490-10 and the output is rated at 90 amps, 240 volts?Here's how to test it to find out if it should be replaced.Unplug the welder.  Connect a voltmeter across the output terminals of the Crydom 2490.  (BE SURE YOUR METER IS SET FOR MEASURING AC VOLTAGE ON A RANGE ABOVE 240 VOLTS AND IS NOT SET FOR MEASURING CURRENT.  Some DVMs are autoranging and do not have to be set for range.)   If you have a second meter, connect it across the control terminals of the Crydom 2490 and set it for measuring DC voltage on a range above 32 volts.  If you don't have a second meter you can do the two measurements sequentially.Plug in the welder and turn it on so it is ready to weld.  You should see about 240 volts across the output terminals of the Crydom.  Pull the trigger of the gun.  You should see a DC voltage between 3 and 32 volts appear on the control terminals and you should see the voltage across the output terminals go to almost zero.  Turn off the machine and unplug it, then disconnect your meters.If the control voltage appeared and the output voltage went to zero, your Crydom is OK and you have to look elsewhere for the problem.  If these two things happen, your control circuit is also probably fine and something is wrong downstream of the Crydom, i.e. in the transformer or its connections or the ground or gun cable.  Examine the connections closely.  There are additional tests to find out where the problem is.If you see control voltage between 3 and 32 volts but the voltage across the output terminals stays at 240 volts, the Crydom is shot and must be replaced.  Since the Crydom appears to be expensive, it would be good to try to find out why it failed before replacing it.  If you don't see a control voltage between 3 and 32 volts when you pull the gun trigger, the Crydom is probably OK and you have to look at the control board for the problem.That Crydom has a pretty high current rating if I'm reading the 90 amp rating correctly.  SSRs with ratings up to 45 amps/240 volts are readily available for $10 or $20 at surplus, but I've never seen a 90 amp unit in my surplus scrounging.   You COULD replace it with a surplus dual SCR module for $5 or $10, depending upon your surplus scrounging skills, but it would take some fussy detail work and a little extra circuitry to make it work with your available control voltage.  You would be much better off finding a replacement Crydom 2490-10(?).Start by going to the Crydom web site and search for distributors in your area or mail order distributors.  Here's one source of new units for a little over $70:http://search.digikey.com/scripts/Dk...0-10&x=25&y=15Here's another mail -order source, a little over $60 but 2 or more weeks lead time:http://www.mouser.com/Search/Refine....user_WildcardsLet us know what you find in your tests.Good luck.awrightPS  As an aside to you and others, we could have saved you a lot of time if you had listed the manufacturer and part number and the ratings printed on the SSR in your first post.Last edited by awright; 05-01-2008 at 02:04 PM.
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