|
|
Hi Everybody !I recently picked up an SP200 mig welder from a body shop. They hadn't used it in a while since they purchased a newer welder. When I got it home I powered it up and tried the trigger, it fed some wire and arced when I put it against the ground clamp.I didn't have a bottle of gas to try to run a bead. The wire that was in it was pretty nasty and there wasn't much left so I didn't run much of it.I went to the welding supply and picked up a roll of wire,bottle of wire lube and a liner just in case the old wire had messed up the old one.I loaded the new roll of wire, turned up the wire speed to run it through the gun. I pulled the trigger and it started to feed ,,, then a cloud of nasty brown gas started coming out of the vents. I shut it down and pulled the cover to see what it was. I turned it back on and pulled the trigger and one of the capacitors was blowing this brown stuff out of a small hole in the top. I shut it down , checked for stored juice in the bank of capacitors and pulled the faulty one out. I then plugged it back in and pulled the trigger again briefly trying to run the wire the rest of the way out, and another capacitor blew. It has 7 capacitors in paralell. What is causing this ? What do I look for ?Thank You !!Tom
Reply:Cap bolts are loose
Reply:CruizerPlease explain ,,,,, what cap bolts ? If you mean the small bolts in the terminals of the capacitors,, they are all very tight.Thank you Tom
Reply:Loose cap bolts are generally the cause for a cap blowing up, or debris on the rails that hold the caps into place shorts, and the whole bank becomes weak. So one after the other fail.
Reply:CruizerThe inside of this machine was very dirty,,as I said it came out of a body shop and was full of dust.I didn't see anything that would be shorting them out on the rails,, do you think the heavy dust accumulation could be to blame ?So do you think I will be able to get by with replacing the two capacitors that are blown,, or will I end up replacing all 7 ?Do I need to look for anything else before replacing the capacitors ?Besides Lincoln is their a source for these capacitors ? Any idea of cost per ?Can you vary any on the specs of the capacitors ?Thank You Cruizer !TomLast edited by Iowax475; 11-22-2008 at 08:33 PM.Reason: incomplete information
Reply:Probably just over heated them, might want to check the voltage going on these rails and compare the voltage specs on the caps. And no its not a good idea to change to a different spec cap.Change one, and its best to change them all out at the same time. Look on Ebay for the same cap.
Reply:CruizerAfter looking on Ebay, and contacting several capacitor suppliers I talked with my local welding supply and I can get all seven caps for under $250. This still keeps this welder "A good deal" considering the price I paid for it and the price of the new ones with similar capabilities.I'm in San Diego right now ,, but will be home the 19th and will pick up the new caps and see how that works out.Is there anything else that I should check out before installing the new caps ? Any other reason for blowing caps other than age and possible overheating in it's history ?Could you or someone on here tell me when this machine was built ?SP200 serial number : AC-561059 CODE 8765Cruizer, thanks again for your help on this issue !Tom
Reply:According to your serial number it was mfg in 1983. Still one of the best mig welders ever made in my opinion.Gary Haunemail [email protected] http://haunsystemsrepair.com
Reply:Thank you Welderdoctor !I was curious as to how old it was and that would probably be a good reason why the caps are going bad ..The man I bought it from told me that the welder came with the body shop business when he bought it and that they hadn't used it much at all since he got it,,,, so it has been sitting.I couldn't believe how much paint dust and bondo dust was inside of it.When I started blowing it out my wife came out to see if I was ok. She said that from the house it looked like a cloud of smoke coming from the shop.Thank you for the build date ,,, I think the new caps and a little fine tuning will make for a good old welder !Tom
Reply:Got the new capacitors installed in the SP200 !!Welded with it a little bit,, it seems to do alright !Thank You to all that helped with the diagnosis and all the other information supplied !!!Now I need a project to really put it to the test !!Thanks again everybody !!Tom
Reply:What are all the numbers on the case of the capacitors? There should be at least capacitance, working voltage, and temperature rating and possibly a date code.Do you have a schematic diagram that you could post?Electrolytic capacitors have high capacitance for their volume by using, not a physical plastic or oiled paper film as the insulating layer between electrodes or "plates" inside the capacitor can, but rather by the electrolyte (the stuff that puffs out when the capacitor fails) forming an insulating dielectric chemical reaction layer on the surface of the aluminum foil in the capacitor. The capacitance is high for a given volume because the dielectric chemical layer is extremely thin - much thinner than can be achieved with physical film dielectrics - and capacitance is inversely proportional to dielectric thickness (and dielectric constant).The voltage across the capacitor in normal use maintains the integrity of the dielectric chemical layer. When an electrolytic capacitor is unused (i.e., has no voltage across it) for a long period of time this dielectric layer can deteriorate, resulting in reduced insulating properties. Then when the equipment is returned to use and rated voltage is suddenly applied to the capacitor, it can conduct excessive current or short internally catastrophically.The solution is to "reform" the capacitors by applying much less than rated voltage when the equipment is initially returned to use after an idle period of many years and increasing the voltage gradually over many hours (how many I can't tell you, but capacitor manufacturers can) while monitoring and limiting the current into the capacitors. The safest way to perform this reforming is with an external adjustable, current limited power supply but, provided the equipment can tolerate application of reduced voltage (depends on the design and sophistication of the electronic controls), the reforming might also be accomplished by powering the equipment from an adjustable AC power source like a variable autotransformer (Variac).When normal operating voltage is applied to the capacitor bank with weakened dielectric layers, excessive current can flow resulting in either overheating and venting the electrolyte through the little (typically red) rubber pressure release vent on the top of the capacitor, or in catastrophic failure as the entire capacitor bank discharges abruptly through the point of breakdown inside one of the capacitors. If you didn't observe a dramatic burnout, but only venting of "smoke," from one or two caps sequentially, possibly you are lucky and only the capacitors that vented are damaged. Once venting occurs, the capacitors that vented are ruined and must be replaced because they have lost, and possibly changed, the electrolyte. The others MAY be OK or may have been weakened by overheating, but at the price you mentioned, I'd consider trying to resurrect the remaining caps by carefully reforming them. Examine the red rubber button on the remaining caps. if they are broken or cracked or if there is a deposit around them, the cap should be replaced. If they look OK after cleaning dirt and crud off them (soap and water is OK, followed by a thorough rinse and drying), consider reforming them. (You can't restore a capacitor that has vented by cleaning it up.)Reforming is not a difficult process and we may be able to talk you through it, but since I gather that you are not very familiar electronics, I'd recommend finding someone locally to help you out. One possible source of assistance is a ham radio operator - not the current crop of appliance operators but an old-timer that built his own transmitters. Try contacting a local ham radio club or an electronics teacher at a local high school, night school, or community college. They'd probably be very pleased to strut their stuff and help you out at the same time.With a bunch of capacitors in parallel (and with the entire areas of the "plates" inside the individual capacitors effectively in parallel), the point of the entire array with the lowest breakdown voltage will fail first, shorting out the entire capacitor bank and possibly protecting the rest of the array if a fuse opens or if the operator shuts down the equipment.I'm not saying this is definitely the mode of failure of the capacitor bank, but it seems likely to me with a machine that had been idle for years.It's difficult to say how critical the values of the capacitors must be without seeing a schematic, but I'm guessing not very. Electrolytic caps normally have a very large tolerance on capacitance anyway - the tolerance ("+XX% -YY%) should be shown on the capacitor case. You can definitely use caps with HIGHER than original working voltage and temperature ratings, although the higher rated units may be a little larger. You can probably use caps with values varying by +/- 20 or 30% and possibly more from the originals, especially when they are part of a bank of 7 caps (assuming you can still use the originals after reforming). I'm guessing that these caps are storing the energy of the rectified line voltage in which case the values would not be critical. While EACH cap in the bank must have high enough ratings for the application, there is no matching required. HIGHER voltage and temperature rated caps can be intermixed with the originals with no negative effect whatsoever.You might be able to find suitable caps in electronic surplus outlets, but you risk getting units that need reforming. Old caps are ALMOST always OK for immediate use, but no guarantees. You might inquire about a recent date code before buying. (All my old huge caps are in storage and I can't actually say they have date codes.)Have fun.awrightLast edited by awright; 12-31-2008 at 03:32 AM.
Reply:Here are the welder and cap specsserial number : AC-561059 CODE 8765 According to welderdoctor it was built in 1983. Mallory capacitor: type CGR11000 MFD 50VDCPOS +85CMAX SURGE 75VDC513490-78235-8326H 2" diameter3.125" tallI was able to find a few caps that probably would have worked,,, the problem was the physical dimensions. They were either taller,or bigger diameter which wouldn't work in this application.All 7 caps sit side by side in a row with 2 angle iron rails that attach to the terminals on top. The rails have insulated brackets that hold everything in place. All the caps I found had at least one dimension that wouldn't allow mounting in the original configuration.I wasn't interested in making all new mounts and connections. The price of the 7 new caps still allowed me to have a good older welder for a price that is under what a much smaller unit would cost. The previous owner aquired the welder when he bought the building and it had not been used in several years so what you were saying about caps sitting unused and then having full power applied makes sense. I still have 5 good (???) caps that have not " vented ". I may try your suggestions when I have more time. I only get home a few days at a time,, so time is precious to me. I hope to get off the road and find work locally but,, with the economy as it is,,, that might take a while.I appreciate the information and will try your suggestions as to " reviving " the remaining caps sometime in the future.Thank You !Tom
Reply:Well, the low rated voltage of the caps means that my guess about the probable function of the caps in the SP200 was wrong. It would be very helpful to see a schematic.Remember that you might be able to stuff capacitors in odd corners and connect them to the existing capacitor bank with heavy stranded wires. This would be problematic only in the case that the caps are part of a fast-switching inverter in which the inductance of the leads could introduce a problem.To reiterate, you probably don't have to match the exact capacitors. You probably only need about the same total capacitance and adequate voltage and temp ratings in however many caps it takes. Here are a few that I found in a quick search of some surplus outlets that I am familiar with. These are listed at Apex Electronics in North Hollywood, CA, a veritable treasure trove of junk:http://www.apexelectronic.com/e-lytic_capacitors.htmIMallory 4300 MFD 50 VDCItem # EC12-CW $2.00 USD Sangamo 7300 MFD 75 VDCItem # EC15-CW $2.00 USD Sprague 2600 MFD 50 VDCItem # EC29-CW $2.00 USD GE 6800 MFD 50 VDCItem # EC44-W-8B $2.00 USD Subtotal: $8.00 USD If you are attracted by the prices here (or elsewhere) it would be beneficial to investigate more carefully the specific properties of the selected caps on the manufacturer's website. Note that the 77,000 MFD of your present 50 VDC bank MIGHT be replaceable with ten or eleven of the 7300 MFD 75 VDC caps above for about $30 plus some creative fabrication, hassle, and wiring. This is just one random example. A little searching would probably turn up some caps closer in value and maybe size to your originals.awright
Reply:In high current power supplies, the equivalent series resistance of the capacitors is very important. This is not always listed in the specs. I would operate the unit for a while and see if you can hold your hand on the caps. They shouldn't get much over 100 degrees if things are OK.
Reply:Hi everyone ! Have been on the road since I last posted so have not had a chance to do anymore with the SP200.I have a question !!I recently read an ad for an SP200 and the person stated that you could run stick off of this welder,,,, that doesn't sound right to me so I thought I'd ask the experts here !!!SO,,, can you stick weld with an SP200 ?Thank You !!Tom |
|
发表于 2021-8-31 22:23:35