Wanted-Miller Coil

Date 03-13-2008 13:34

I think you are describing the three coils that connect with about 15 wires to the range switch. If one of these coils is burned, it usually means a diode shorted. Get the serial number and we can check for one here. weldersales

By Grinder4400 (*)

Date 03-13-2008 17:27

Yes....I have had the local miller tech check this welder. He said the Diodes were ok. At the time he checked this the welder wouldn't start. Had some bad gas in it from sitting. I cleaned tank out ,filter, and carb ...run fine....I checked them myself with a multi meter. Making sure current would only pass in one direction. I measured about 5 ohms on each. Seemed like one measured 3.5 ohms. I unbolted the lead off the diode to isolate it from the rest of the circuit. tested. I do realize these diodes can test ok at a small current but fail at operating levels. The reactor (triple Coil) has suffered a short. Visual inspection of this revealed the center coil darker than the others and you can see burnt rosin on the back. The service manual removal procedure has reactor and blade switch coming out as one unit. This would help me not having to keep track of those 15 leads.

Miller 40G\
Red Seal Continental engine
# JD726595

!Note! There were two different reactors in this year! Part # 036 259 Reactor(prior to JD698329)
Part # 084-814 Reactor(Eff/ with JD698329)
I am not sure how many years this reactor was used after 1983 this is what Miller came up with

1983/July JD698329 JD26
1984/Jan. JE732465 JE1
1984/July JE783729 JE27
1985/Jan. JF835606 JF1
1985/July JF905000 JF26
1986/Jan. JG000500 JG1
1986/July JG071437 JG26

The closer to 83 the better.....

By NMWELDING (**)

Date 03-20-2008 03:11

I also have a Miller Big 40 same model year with the same problem. Center coil burnt. I have other welders but I still would like to get this one fixed. Back when it happened,about five years ago I priced a new one and was told it was $1200.00. Mine takes # 036-259. Welder serial # is JB569796.

By Grinder4400 (*)

Date 03-21-2008 06:04 Edited 03-21-2008 06:06

Yes...Miller has this part and I too remember those prices...Wholesale on that part was in the $800.00 Range....and retail was in the $1200's now its 1200-1600...they still have it on the shelf....But they must like it with that price on it. I have been told by different people that they have seen those get so hot they have about caught fire...mine hasnt opened acording to to my meter. Miller used to sell the individual coils...but say that for $afty reasons they have stopped. With a safty shut down on the water temp and oil pressure not sure why this welder would have a $ 60.00 part eat a 1600.00 reactor in the time it takes to clean the slag off your weld. however I caught it when it first started happening....did turn one lead off the center tap insulation dark. As stated I had local Miller tec check this welder and he said the diodes were fine. I have found one of the strait polarity diodes to be shorted. I removed reactor (sigh) and coated with thermal spray reinstalled and ordered a diode. I will replace all diodes if the rest of my tests are positive. Have 90+ volts between phases. Windings seem ok. Diodes are $61.00 each and there are (6) of them. If i can help please dont hesitate to ask....Good luck with old blue!

By NMWELDING (**)

Date 03-24-2008 21:20

My big 40 now sets in the shop,I don`t use it much. I`m only able to use it because I disconnected the center coil from the range selector switch. With it connected it would not weld, acted like it was under constant load,as in a coil shorted,which I assume it is. I disconnected the center coil from the range switch and now it will weld on the top three ranges,not the first two,also doesn`t seem as hot with this disconnected. Thought I`d try this and it does work,I just would not use it this way and depend on it for a welding job.I did not check out any diodes or anything else,just figured with smoke rolling out from the center coil and with it burn`t looking ,that was my problem. Still would like to fix it someday. Thanks for input.

By Grinder4400 (*)

Date 03-31-2008 13:31

I too had a smoking reactor. One of my strait polarity diodes was bad. I replaced this Diode and checked out everything to make sure the three phase generator was good....about 90 volts between phases. Those reactors are tough...the insulation resin that they are dipped in gets hot when your diode shorts. You can use a regular ohm meter to check to see which diode has gone bad. Im going to replace all the diodes here shortly....If your able to weld in the other positions it would lead me to beleive that your one coil has shorted or posibly even opened. If I run across a used reactor Ill get the 411 on it and send it to you. (these are fun to change btw....:) Let us know how it turns out.
Grinder 4400