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Thread: Same MIG new problem
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18th Mar 2020, 08:33 AM #16Most Valued Member
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I stand corrected now I’m looking at the diagram on a larger screen, missed the connection to welding voltage plus on the right side of the diagram and just assumed the circuit was feedback of some description..
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18th Mar 2020, 10:14 AM #17Most Valued Member
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Hey I never worked it out
Current theory is caps.
242V at house
242V at welder(though granted no load as yet)
Took the top off, three of the caps have a pimple in the top as per pic, one doesn't. Of course its possible they were always like that.
Just came back to the house for my LCR-T4 which claims to be able to read caps up to 100000 µF.
Last edited by Stustoys; 18th Mar 2020 at 11:27 AM. Reason: remove the bit about diodes, turns out there are 6
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18th Mar 2020, 11:27 AM #18Most Valued Member
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Well that's disappointing.
If I have my valves correct, while in fact all four caps don't look great they test ok.
80.67mF
21.57mF
19.55mF
21.35mf
19.83mF
Next
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18th Mar 2020, 08:43 PM #19Most Valued Member
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Evening guys,
My back sure doesn't like bending over this thing lol
242V to the contactor. The insides don't exactly look pretty but would that be the issue?(I'm thinking not.. but hey I don't know)
I could move the wires from the worst set of contacts to the unused set.(that thought would have been handy 6 hours ago lol)
Diodes seem to test fine.(or should I be testing the one at a time? which would mean much more disassembly)
Haven't tested the transformers at all, of course they look ok and smell ok.
Might not get time to look further tomorrow.
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18th Mar 2020, 09:24 PM #20
Hi Stuart,
Those capacitors don't look good ! There shouldn't be any of the damage to the tops at all, and the ESR reading is quite high, I would have expected much less.
The transformer windings must be disconnected from the diodes before you test them, and each diode should be tested individually.
The contactor looks to have been hammered somewhat. Though the contacts can be cleaned up with a bit of fine abrasive paper wrapped on a stick.
I'm guessing but those capacitors look to be favourite, the 80,000 could be a typo with one too many noughts. I did say that it was a big capacitor. Each one will have the capacitance marked on it, so you will know. Just add the values on them together to get the total.
HTH.Best Regards:
Baron J.
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18th Mar 2020, 10:02 PM #21Most Valued Member
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Hi Baron,
No they don't. I pretty sure they shouldn't ones I got them out. I know what ESR stands for but other than that it is pretty much out of my depth.
80k isnt a typo. It wasn't very clear but thats what the values near 20mF were, the individual caps. picture time.
I just wasn't 100% sure I had my micro, nanos and picos in the right order. Though it would have to be a pretty staggering failure of them to all fail almost exactly one scale low or some such.
They are only tested at 9V so I guess they could break down at welding V?
Would powering it up without the caps in place to see if the fault goes away be a bad idea?(I really wish the welding V wasn't feeding the PCB)
My thinking was, if the if the diode failed open it cant be the problem. If if failed short all three would fail the test.
I'll have another look at disassembly and testing again.
I might price a new one. I'm a little more pushed for time ATM.
I'll have a look around for caps to though I doubt they are so cheap as to "replace regardless", but you never know.
Hope that all makes sense.
Thank you.
I'll read the thread/pm again and check what I have missed when I get a chance.
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19th Mar 2020, 02:40 AM #22
Hi Stuart,
They shouldn't be too hard to replace, 20K uf (uf Microfarad) used to be a very common value, particularly in large computer power supplies. Now a confession, about a year ago, I took a box of 48 brand new 22K uf 40 volt capacitors to the scrapyard and weighed them in for scrap aluminium. I got a measly £2.00p for them.
Would powering it up without the caps in place to see if the fault goes away be a bad idea?(I really wish the welding V wasn't feeding the PCB)
My thinking was, if the if the diode failed open it cant be the problem. If if failed short all three would fail the test. I'll have another look at disassembly and testing again.
I might price a new one. I'm a little more pushed for time ATM.
I'll have a look around for caps to though I doubt they are so cheap as to "replace regardless", but you never know.
If there is room in there you can put in bigger value capacitors or multiple smaller ones, just don't go down in voltage rating. The important rating for those capacitors is ripple current rating, the higher the better ! The high ESR value reduces the ripple current ratings of the capacitors. I would expect less than 1 ohm. It is the ESR current that causes the capacitors to heat up and like one of yours, burst and leak electrolyte, that nasty yellowish stuff on the edge.
Hope that all makes sense.
Thank you.
I'll read the thread/pm again and check what I have missed when I get a chance.Best Regards:
Baron J.
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19th Mar 2020, 08:08 AM #23Most Valued Member
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Apply rules 1 and 2, replace the contactor and your welder will work. The loss of incoming line voltage is being caused by the high resistance joints across what is left of the terminals. 240V on the line side of the contactor will be a lot less on the load side once it makes its way through what’s left of those contacts.
Preventative maintenance rule #1... if it ain’t broken don’t fix it....
Despite the cosmetics of the capacitors not being supermodel pretty, they are functioning and test at correct value. I wouldn’t be replacing them for funsies.
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19th Mar 2020, 09:04 AM #24Most Valued Member
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Morning,
Well get down there and get them back It's ok, it always seems to be the way. I tell SWMBO "I know I'll never use 90% of this stuff, but which 90%?"
Yes, that's what I figured but thought I would ask.
But that's my point(I think) if one of the diodes fails short, then my handy dandy tester wouldn't call the "circuit" a diode.
There isnt a great deal of room. A short search hasn't turned up any can neg caps, but I assume they must be out there.
Yes I will start looking for a contactor. It was the problem last time after all.
Would have been nice to test the V on the other side but digital meters dont get time to give a reading.
Have spade connectors gone out of fashion? All the contactors I'm seeing have screw terminals*. Not the end of the world but a direct replacement would be nice.
Or at the very least only replace one thing at a time.
Given they have lasted 35 years and even the cheapest caps my search bought up that "might" do the job will cost me $25 each, I'm in no hurry to replace them... but they might not be long for this world.
Thank you
*OK granted most of the connectors I have ever seen have had screw terminals, but that's not the point
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19th Mar 2020, 09:44 AM #25Most Valued Member
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What model meter is it? Most digital multimeters these days have a minimum and peak hold function that allows capture of a dip or spike.
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19th Mar 2020, 09:51 AM #26Most Valued Member
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If it makes you feel better, my 3year old BossWeld 186 is getting loaded into the back of the Ute and taken to the service agent today for exactly the same fault. 99% certain the relay is fried in a similar fashion to your contractor, but don’t have a schematic, company won’t supply one, or parts for that matter, to home gamers. Expecting a bill for a new control board.
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19th Mar 2020, 10:58 AM #27Most Valued Member
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My best is a Extech EX300. Certainly not the greatest. It's "hold" function holds what is on the screen at the time.
Yeah..dont get me started.. thats a whole other rabbit hole! Its all about "SAFETY" or at least that's what they will say.
I follow some of the "right to repair" that's going on in USA ATM, maybe something will come of it. Some of the things some manufactures are getting up to is pretty shady. Looks like you got me started
How I got a bucket load of brownie points from SWMBO last week was her ASKO front loader was taking far to long on most wash cycles. Short version, heater wasn't coming on, not the element or the thermistor because of course you can buy those. Problem was on the board which of course you cant buy, as luck would have it I pulled it out thinking maybe it was the relay. It was a "dry joint" on the relay! Now I assume it wasn't really a dry joint it was a failed joint from switching 10Amp for all these years. Exactly while it failed I don't know, bad design or perhaps its a sign that the relay is on the way out and perhaps I should replace it(the sure sounds like a good idea now that I think about it)
p.s. and yes it does make me feel a little better ty
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19th Mar 2020, 07:09 PM #28
Hi Stuart, Guys,
Re soldered joints.
With the advent of banning lead in solder, joints that carry a high current commonly go open circuit ! Just resolder it with ordinary tin/lead fluxed cored solder and it will be OK for a long time to come. The lifetime for lead free soldered joints is three to six years before they start failing. Its common practice to simply go around all soldered joints with a flux pen and 60/40 cored solder. I've salvaged a number of flat screen TV's and monitors simply doing this and nothing else.
I don't think that I've ever seen spade connectors on contactors unless they have been fitted by whoever was installing them. Their high current reliability is quite poor.
As far as your tester is concerned, if it detects any difference in forward and reverse readings then as far as it is concerned then it is a diode even if it has shorted out. This is actually a little deceptive, because even after a diode has failed and no longer has the ability to rectify properly there is still a silicon junction of sorts in there. A proper ohmmeter can tell the difference simply because it will apply a higher voltage and more current when testing them.
I hadn't realised that your welder was 35 years old ! Those capacitors have done well to stand up to the high current charge/discharge cycle over the years. As far as I'm aware all large aluminium can capacitors the cans are the negative terminal, even some wire ended ones. At the age that those capacitors are, it is likely that they are oiled paper ones, though the damage to the seals on top is typical of electrolytic capacitors.
By all means continue to use them, but be aware that they are potentially failed !
RacingtadpoleIf it makes you feel better, my 3year old BossWeld 186 is getting loaded into the back of the Ute and taken to the service agent today for exactly the same fault. 99% certain the relay is fried in a similar fashion to your contractor, but don’t have a schematic, company won’t supply one, or parts for that matter, to home gamers. Expecting a bill for a new control board.
If you are sure that the contactor/relay in your welder has failed in a similar way, then why don't you set to check and replace it ! Its got to be cheaper than paying out for someone else to do it !Best Regards:
Baron J.
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19th Mar 2020, 08:49 PM #29Most Valued Member
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Sometimes being to busy to work on things I would like to pays off, it seems I think slow
Sure I cant test the contactor with the welder, but its easy to put a load that's not going to trip the breaker on it and I can test until the cows come home, unless the breaker still trips which is also an answer. So in the interests of science I will test it then clean up the contacts and test again.(which is strange given "coz I don't have time to play" I just spent $65 on a wire hose clamp tool that I could knock up in the shed in less time than it will take me to play around with this contactor, but sometimes I'm a little crazy)
hmm I'd heard of the dislike of lead-free, but I've not heard it in those terms before. Thank you, certainly something to watch out for.
Well ok then. Best practice to use ferrules under the clamps?
Ok, something else to watch out for.
Ty
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20th Mar 2020, 03:27 AM #30
Hi Stuart,
Well ok then. Best practice to use ferrules under the clamps?
cable end.jpg
Like these, but the ones that I was talking about have the end of the fork turned up at 90 degrees for a short distance.Best Regards:
Baron J.
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