Reactor in a portable Miller Big 40 welder?

I had an hour today and i did get it to work. I pulled the diodes out and checked, they appeared to read good, all were very close in reading. I scoped the output dc and had minimal ac on the line. The fine current adjust was checked with a fluke and also appears to be good, a couple bad spots in it where we always have it set at, but not causing the problem. I then had someone weld with it and it welded, with both the range switch and fine current set to minimum. This was with a large electrode, so i could not get a nice thin weld as it used to do. I then took off each lead # 17, 27 and 37 one at a time and tried the welder out at the above mentioned settings. # 37 did the trick and the unit operates as it should. This is without one of the three coils of the reactor. Can i now assume that even tho the coils all read the same, the one associated with #37 has some varnish worn off and allowing part of the windings to short together? I did not have time to read individual coil windings and am not even sure it is possible. Will it badly damage the welder to operate it this way? We are lucky in the fact that we have 4 other welders that are newer and nicer than this one, i just did not want to trash this one......again, thanks to all of you!!!

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Originally Posted by inillinois2

I then took off each lead # 17, 27 and 37 one at a time and tried the welder out at the above mentioned settings. # 37 did the trick and the unit operates as it should.

Can i now assume that even tho the coils all read the same

with an ohmmeter?

, the one associated with #37 has some varnish worn off and allowing part of the windings to short together?

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It has somehow lost inductance. If you pass 60 Hz through each coil of Z1 with a transformer you should see a difference in #37. If you don't, I am stumped. The problem is that the coil permeability probably changes with current so you might have to pass 100A of AC through the coil to read its design impedance value.

And with Z1 set at low current and a constant load on the welder the scope should show one of the three phases higher than the others and not adjustable.

If R equals the DC coil's resistance and X equals the coil's impedance and XL equals the coil's inductive reactance, then X² = R² + (XL)². If the coil is primarily inductive reactance, an ohmmeter won't tell you much.

If you have the schematics for the other welders and they are still working, I'd start measuring whatever components in each one that doesn't show a schematic value for resistance or inductance. For this one I see 10 unmarked coils.
BTW, the resistance of VR1 will vary with the voltage applied to it.

BTW, MIG welders are described as Constant Voltage sources, so arc welders might be more like Constant Current sources, with the SR3 diode bridge acting like a current summing network and VR1 acting to limit open circuit voltage, which is theoretically infinite for a CC source. That's probably why the SR3 diodes have such a high PIV.

Wires #11,21,31 are the AC inputs to the Z-1. You can put a voltmeter on those and read that voltages phase to phase. It should be close on all 3. You can also put a meter on 17,27,37 phase to phase and see if those readings are close. Weather does effect those coils and whoever diagnosed the machine as having a bad reactor seems to have made the right diagnosis OR you have a wire shorted across another wire in the S-3 range switch.......Most Miller SM's have a voltage and resistance chart for testing. It would give you test points and the proper voltages you should see in all ranges. I will take a look tomorrow at work on my Miller website connection to see if I have anything more helpfull. That is an older machine and many of the old machines have limited info available and parts like that reactor are often unavailable new from Miller.....If it was available it would be quite a job to change and very expensive. I have changed similar transformers on at least one or two similar machines in the past....

With a constant 200A or 300A load on the welder a clamp-on ammeter should show higher AC current in wire 37.
If you do need a new coil maybe a motor rewind shop can help.

It is extremely unlikely anyone can make a reactor for this machine and or repair the one you have.

There is a full SM available and it is T-450 for those machines. You can buy one from Miller for $15.00

Millers have a serial number on the front panel. 2 letters and 6 numbers. It is stamped into the front panel. That number is needed to be sure to get the right part.

There are 3 different S-3 switches listed and 2 different Z-1 reactors. One is not available from Miller. S-3's range in price from about $450 to $675. The Z-1 available from Miller is $1650.

I make my living repairing electrical equipment like this. Miller and Lincoln welders and generators from Onan, Briggs and all the big standby manufacturers.

You cannot repair equipment like this with without buying the proper parts from the OEM. Your wasting your time theorizing about this and that. Get a SM.....test the parts and replace what is necessary to do the proper repair or replace the equipment. Or take it to an Authorized Miller service repair facility......

You can fix it yourself. No problem. Take a look at this African Welder.

http://imgur.com/MTzja.jpg

Very nice welding there JugDish. Where are your gloves and shield? Oh you don't need those, righhhhht! Mr Miller would be proud of your ingenuity....thats what he did back in the 20's or 30's

I think you can get a coil wound right in the back of most any Dunkin Donuts or Quick Check....WalMart super centers also might have a dedicated group of coil winders in the back.........:rolleyes:


It's all in good fun here gents.....

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Originally Posted by jimbo

You can fix it yourself. No problem. Take a look at this African Welder.

http://imgur.com/MTzja.jpg

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I wonder how they make their Hi-Def TVs. . .:eek:

I guess you could leave wire 37 disconnected, if the inconvenience of this 'costs' you less in dollars per week or dollars per usage of this welder, than the one-time cost in dollars to repair.

Please post back how you decided this issue.:p

Am leavin the welder as is with one lead of coil unhooked. Usage is pry only about 20 hrs a year and have brand new Miller Bearcat 300 to use plus 3 other portable (propane) welders. Thank you all for your help on this matter, maybe look u up when the TMC 150 Thermatool) goes haywire, but can usually handle it! Thanx again !!!!

Now if an OP comes along with a bad MIG welder, we can all reverse-engineer that thing. :p

Mig welder = AC input power....main tranformer.....main rectifier.....cap bank.....stabilizer (Z-1 again)......control section......solid state for new style.....contactor, relay and pots for old stuff......wire feed motor drive and gas solinoid and a gun......No reverse engineering needed on those just bring it to me and I will fix it.......




P.S. I have never heard of a Miller Bearcat? They make Bobcats, Trailblazers and have one machine called a Wildcat but no Bear cat that I am aware of anyway.......Whats in a name anyway? They are engine driven welder-generators and some are also Inverters........I have worked on most everything they make from big to small...Mig-Tig-Stick-Inverter.....


P.S.2 for my friend ThatGuy the engineer........If you want a real challenge....try an Inverter based machine....good luck! LOL.... and be sure to be carefull there.......the cap bank on some of those machines has over 900volts of stored energy after the power is OFF! You could reverse engineer yourself right into the hospital with one false move......

Excuse me for the name mix-up, bobcat. Is brand new and right out of the box. haven't really even looked at it...........thanx for your input tho.

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Originally Posted by Rich B

the cap bank on some of those machines has over 900volts of stored energy after the power is OFF! You could reverse engineer yourself right into the hospital with one false move......

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I'm surprised I don't hear about people being killed while fixing microwave ovens. Supposedly, over 1 joule of stored energy can be fatal.

I have never touched a Microwave and know zero about them. I have a Litton that is probably 25 years old and works fine. I don't use it much anyway. If it failed I'd throw it out in a heartbeat especially after reading some of this...



http://www.repairfaq.org/sam/micfaq.htm#micsaf