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02-23-2019, 01:51 PM | #1 |
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Capacitor testing
I know there are some members with solid electrical backgrounds and I need some help troubleshooting my mig welder. It is a 100 amp unit, 110v. Lately it is not working well. It seems to not be generating a hot arc like it used to, it also feeds the wire slowly. The symptoms seem to have appeared abruptly between uses but I don’t use it very regularly. I don't see any loose connections and the main capacitor does not appear to be swollen or leaking.
Is it possible to check the capacitor with a multimeter sufficiently? How is that done? I googled but what I saw does not seem like it would be an accurate measure for this large a capacitor. It has been unplugged a week but I have not tried to unload it and am reluctant to short across it. Thanks. |
02-23-2019, 08:51 PM | #2 |
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Re: Capacitor testing
You need a common analog multi tester to check it.
FIRST, put the meter on "DC VOLTS" scale. 100v or more. Put the red lead on the "+" terminal of the cap and touch the black to the other terminal to see if there is any charge left in the cap. If it shows anything over 100 volts, let it sit some more till it goes below 20. When it gets that low, you can short it. Shorting a large cap with a big charge in it can burn the leads off inside the cap. If it shows no voltage, short the cap with an old screwdriver to be sure it is safe. THEN, put the multimeter on a mid to high ohms scale. Put the red lead on the "+" terminal of the cap. put the black lead on the "-" terminal and note any meter movement. If the cap is good, the meter will deflect up momentarily and slowly go back toward zero. If it does not go clear back to zero, the cap is leaky. If it goes up and stays at some level, the cap is shorted. If the capacitor terminals are not marked, try the test one way and then reverse the leads to get results. |
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02-24-2019, 12:20 AM | #3 | |
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Re: Capacitor testing
Quote:
Do you have a schematic? Do you have the Make and Model of the welder? Let's go from there. It might be easier to swap a new cap into the unit rather than testing that nasty cap. |
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02-24-2019, 10:28 AM | #4 |
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Location: San Antonio, Texas
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Re: Capacitor testing
It may not be a cap causing your problem. Check this link. https://weldingweb.com/showthread.ph...What-are-signs
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02-24-2019, 10:42 AM | #5 |
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Re: Capacitor testing
Also check weldingtipsandtricks.com, I have a millermatic 180 and the wire tension knob usually needs adjustment after heavy use.
If it is a new spool of wire the drive roll grooves need to match the wire diameter, cheaper wire may not be of the proper spec. |
02-24-2019, 02:12 PM | #6 |
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Re: Capacitor testing
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I appreciate the help. |
02-24-2019, 02:27 PM | #7 | |
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Re: Capacitor testing
Quote:
It is NOT shorted. |
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02-24-2019, 03:01 PM | #8 |
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Join Date: Jun 2014
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Re: Capacitor testing
Quick follow-up, I read the thread on cleaning the feed wheels, tension and inspecting the cable housing suggested by rotor wrench and 39portlander. There was some schmutz and I cleaned everything, rotated the housing even though I couldn’t see any wear, and put it back together. No joy. The arc is still weak and unstable. I hate swapping parts for troubleshooting but don’t see an alternative at the moment.
Pete, I did not see your response until after I added this comment. I don’t have a wiring diagram as suggested by Red. Any ideas on how/where I can get this tested to nail it down? |
02-24-2019, 03:18 PM | #9 |
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Join Date: Dec 2013
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Re: Capacitor testing
Have you tried Digi-Key? I get most of my electronic components from them. They seem to have the best prices and fastest shipping. Their product selection is huge, and you have to know what you're doing just to get around their website, but it might be worth a try.
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02-24-2019, 03:36 PM | #10 |
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Re: Capacitor testing
I have gotten those big value caps from Fair Radio Sales. They are usually under 5 bucks.
Sometimes you have to gang 2 or 3 up to get the value you need. |
02-24-2019, 06:50 PM | #11 |
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Re: Capacitor testing
See > https://www.weldingandcutting.com/Ca...s13490-109.htm
59,000mf, 40Vdc Capacitor for Century (213-035-666) and other welders. 9SS13490-109 Description $86.33
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03-11-2019, 01:34 PM | #12 |
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Re: Capacitor testing
Just a follow-up, I replaced the capacitor, using the one shown above. This was the only result I found googling. The welder seems to be working ok but I am withholding judgement until I use it a while since it was intermittent. I didn’t try stacking smaller (cheaper) caps because if it didn’t work I am not smart enough to know if it was a welder problem or modification problem. One more thing, turns out there is a wiring diagram on the inside of the side panel. I didn’t notice until I was putting it back together, not sure if I am getting less observant or less interested. Thanks everyone.
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03-11-2019, 02:28 PM | #13 |
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Re: Capacitor testing
When the welder at work got weak I found connections at the transformer had corrosion, aluminum windings to copper connections
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