[DennisCA]

I bought a new to me welder recently, a 300A machine of the brand Kemppi, it's an older machine, 1990s era, DC only. It's got stick and TIG functions and some advanced functions (slope, tig spot function, minilog, pre-post flows, lift-arc and HF etc).

But it does have a strange quality, it squeals when you weld with it and the noise changes based on the arc length, same in both stick and TIG mode. I sorta find it helpful as I can use the noise as additional feedback on my arc, but also a bit annoying...

BUT, I've googled it and from what I can see a lot of these Kemppi machines are squealers and it's part of normal function. My question is why? It seems to apply mainly to older machines, does it have something todo with older inverter technology used in these machines perhaps? Does the fact that it's a 3-phase machine result in some design quirks that lead to this noise?

I found one reference to a kemppi being a squealer:
http://weldingweb.com/showthread.php?34 ... vice/page2

It's just flat out a "stud" and if you ever see what the slower frequency inverters (squealers) do when tig-ing or stick welding sluggish fillers it's amazing. (it will even "pulse" SMAW which is just evil with Ni-rod).

So is this perhaps the reason? If I get this right older models of inverters where slower frequency and have a tendency to squeal, so is this the reason? And they apparently have nice welding qualities? If so why aren't they around any more?

[Poland308]

It's due to the inverter harmonics. It happens to most of the older 3 phase inverters. I've herd Lincoln's and Miller's do it as well. Lots of motor freq drives make squeezing noises as well. With them you can vary the pitch by changing the frequency. I know with the freq drives for motors that some manufacturers offer a sorfware update that seams to help. I believe it changes the rate and order of the switching of the internal components.

[DennisCA]

Taanks for clearing that up! I am currently working on the machine, the LCD display that shows the current isn't working properly, only seeing part of it and it doesn't even seem to change with the potentiometer. So I took it apart:





Here's the display itself, mounted on a circuit board.








All in all the insides of the machine look very clean, aside from the board that has the display, it looks dirty and mybe that's the culprit. I've been advised to clean it using compressed air and/or isopropyl alcohol, perhaps move the LCD itself and see if I can clean the contacts.

[Lightning]

I used to use a Miller XMT (forget the exact model) on single-phase power, and it squealed too, mainly when starting the arc. I was told it was normal for inverters.

[soutthpaw]

The older SCR inverters like the Powcon brand and probably the new Arcon brand are known for squealing like a pig. It's normal

[DennisCA]

I did some googling on PowCon and apparently some of them where just rebranded kemppis!

[Arno]

All in all the insides of the machine look very clean, aside from the board that has the display, it looks dirty and mybe that's the culprit. I've been advised to clean it using compressed air and/or isopropyl alcohol, perhaps move the LCD itself and see if I can clean the contacts.

The LCD looks like its a fairly common module in itself. If it turns out to be bad likely there's a type number on the back and you can probably find replacements on Ebay and the like.

A few ideas..

While you have it open and are cleaning things out, visually check all the electrolytic capacitors (the blue cans on the ciruit boards) for signs or damage like bulging, inflation or burst open tops.

As electronics age and especially all types of power supplies (which this basically is ) these are the components that tend to wear out and fail. The rest is fairly stable age-wise. Some resistors can drift value-wise as they age, but for this application it's likely not that important.

Replacement of capacitors can be time consuming if you have to strip down a machine and solder in new ones, but capacitors are not that expensive so the amount of money is usually limited.

Late 80's and early 90's stuff is still OK as far as capacitor lifespan goes, but there was a major supply problem with badly made capacitors (also counterfeit ones..) flooding the market in mid/late 90's which caused major problems in many devices.

Examine any back sides of circuit boards you can see with a bright light and check for any solder joints that may be developing cracks around the pins. Usually visible as a circle/ring around the pin that sticks through the cicuit board. A simple re-flow usually takes care of that.

Also unplug and re-plug interconnections between boards and perhaps threat them with a good contact cleaner and then treat with a corrosion inhibitor. Helps to remove any oxidation that's built up over time and restore good contact.

Bye, Arno.

[DennisCA]

Thanks for the tips!

This one is made in 1994 going by the PCB date. I had a look at the ones in the PCB I took out and they looked fine as far as I could tell. The broken LCD had a visual crack in it near some connectors, so probably what is wrong.

EDIT: The underside of the LCD says Hamlin 8938-390-236-592-000 but I cannot find anything for that.
I was able to identify the graphics driver though:
https://datasheets.maximintegrated.com/ ... CL7117.pdf

[soutthpaw]

I did some googling on PowCon and apparently some of them where just rebranded kemppis!

I know they sourced some feeders and other parts from others but the guy that basically invented the inverter welder started Powcon. 100% made in USA. He started Arcon after Miller bought Powcon. You can call and talk with him. I've owned 1/2 dozen of the Powcon machines

[DennisCA]

I stand by what I said. Some of the Powcon machines, were kemppis, you can easily recognize them because they are just a Kemppi with another paintjob and basically have 100% parts compatibility, like this example which has the same shape and the easily recognized kemppi style front:
http://i.ebayimg.com/00/s/MTUxMlgxMzUz/ ... l/$_35.JPG

This model is a Kempotig 250 AC/DC in different colors:


(edit: bbcode error)

[soutthpaw]

I believe anything not in the standard Powcon box with handles was made by someone else. But all the ones that look like this are USA made and designed by Powcon. Those are 2 I used to own. Same machine except the tall one had dedicated 6010 ports.

[DennisCA]

Yes those are definitely powcons through and through.