Miller 300D Low hours with no A/C output

[Syleng1]

Good morning and thank you for allowing me to post -newbie

I have in one of my welding trucks a 2000' Miller 300D Trailblazer with the Diesel that is fully loaded (and super loud.) It is basically a 50/50 machine. It runs 50% of the time for the electrical and 50% for welding. Welding is 1/8" rod (110amp) and runs a Profax spool gun direct wires thru the 14pin amp plug with E70s .035".

My issue is the A/C power side is cold when I tested it with a meter. About 5 years ago I had to have the rotor and brushes replaced because the brushes wore thru the slip rings and shorted the machine. The bill was over $2000.00 with the past ABCO welding supply. They did a great job but is now owned by Airgas so the answers do not flow as easily as the family run company did. This happened because I was told the machine was "brushless technology" by the Miller rep. He did not tell me the whole truth.

I pulled the side cover and checked the brushes - still have life and the slip rings are not shot but a bit glossy for my likes. The usual draw is a 4hp 240v 1ph compressor motor that has been on this machine since 2003 and a Thermal Dynamics TD-50 plasma cutter and or hand grinders / drills or drop lamps. All normal over the shelf stuff. This machine has a split rotor producing welding power separate from generator power. Right now I have no power from the 240v plug or the 4 @120v outlets. When I probed with a mulitmeter I got about 22-24v a/c thru one leg of the 240 plug. That's all.

Does anyone have a electrical schematic or service manual on this machine? Being over 10years old, information from Miller is hard to come by. I am leaving for a week of vacation tomorrow (Monday) and would like to be able to diagnose it today so the parts are in when I return so I can go to work. I hate to carry this energy with me on the vacation. For me, if the machine is shot (not that it is) I can order a new machine and move on with life. Not knowing is a very heavy weight to carry when the family needs me to be relaxed for a week.
Thank you for your help.
Joe

[tprothma]

The first thing I always do is to clean the slip rings.
Use 500 grit sandpaper and clean by hand, sometimes 400 grit but never below and if I use 400 I go very, very slow.
Clean 1 side, turn the motor a little, clean again.
Repeat until you get them looking like a shiny penny.
Tim

[duaneb55]

Got a unit SN? There are 4 different manual SN ranges for the 2000 model year.

[duaneb55]

And it still welds?

[duaneb55]

Owners Manual can be had here if you don't have it:

http://www.millerwelds.com/service/l...&submit=Search

[Syleng1]

Thanks Duaneb55,
I am at home and heading there soon and will get the s/n from this thing. All I remember when I bought it new was the salesman from Miller did not even have one to show me and when I ordered it; it came directly from Miller plant. It was made for me. Sadly, when the rotor and brushes were replaced the unit had to have the rotor built because it was a 1st generation machine.

Yes it still welds, and if I had to do it all over again I would but I would had installed a darn 2nd muffler as this thing screams loud.

I found the owners manual and of course when I bought this thing new I did not write down the number but it is a 300D NT and I will use the trouble shooting list to eliminate a few items before I head to the dealer.

Tprothma: These should be the 3 slip rings if facing the control panel are right behind the right side service panel correct?

Thanks,
Joe

[Syleng1]

Duaneb55,

I need to retract a statement, I was misinformed as mine was an original. Going by the list you sent me of owners manuals, mine is Feb2000 printing of the manual and they list this machine back to 98' Kind of frustrating that I bought this unit and was told it was a brand new model. Dang sales people. Same guy who told me it was "brushless." I was buying a new machine for a new truck and just before I did I had a Legend with the 20hp Onan do the same thing on me so "Brushless" sounded awesome.

Anyone reading this better realize that the internet in the year 2000 was not at all like it is now. There were no forums or information sites like this back then sadly.

Joe

[duaneb55]

Brushless huh? Salesman must have been a greenhorn.

If it still welds but no AC auxiliary power I'd be looking at circuit breakers CB1 and CB2. Check for 240V AC power coming into them at wires #51 and #53. If no power there, you're going to have to check auxiliary power stator windings.

[Syleng1]

I was wondering about those if they do go bad. I've only popped them once or twice when it was very cold and the compressor did not unload air pressure (motor trying to compress -compressed air.) Not good. Chances are they are ok and its something major. Then again the main plug for the 240v (the big 50amp dryer looking plug) for the last month or so I have to "twist" it every so often to get the compressor or plasma cutter to work. Both units are wired in the truck to a circuit breaker panel in the truck. Then it goes to both units with their own plugs and circuits. The generator portion will run both at once but plasma output is low when the compressor runs. I unusually just stop and let the compressor cycle and shut off and go back to cutting. I also need to check the fuses first as they can and will go bad or vibrate out.

It's all good I just hate to spend another $10k if I don't have too on a welder. If I do I want something really quiet. But I can buy a good set of ear muffs for that much money if I can fix this unit. For $14k I can buy the unit with the built in air compressor and forget about the power draw all together. My choice is to save that money for employee paychecks and keep them happy.
joe

[Syleng1]

I wanted to post an update on what my findings were AFTER I returned home from vacation; had to start my day repairing my own stuff before I could go to real work.

I pulled the side covers and inspected the brushes - all looked good approx. 7/16" left in length. I checked all the fuses and circuit breakers for operations and all was fine. I double checked all the grounds and the ohm check of the rotor was good. I decided to pull the brushes and found the furthest one in #3 the cable from the brush to the stud torn? So I went ahead to sand the slip rings on the rotor (where the brushes ride) with the recommended 800 grit sand paper and slip ring #1 (furthest from the engine) cleaned up like new. When I went to clean #2 the slip ring was loose! #3 also was loose. I actually started to shake when I ran the engine with the starter and fuel shut off.

I decided to bring the unit to Airgas (a major customer of mine) and dropped off the machine. Nice part as the rotor with slip rings was replaced approx. 5 years ago and 400hrs ago to the tune of $2,000.00 for the worn out slip rings. These guys are good and I've trusted them with a lot of my other machines. So fingers crossed as a $2k bill is better than a $10k for a new machine.

Thank you for your help!
Joe