I am looking for some info on a "reactor" that is in a potrtable welder. This reactor is basically a transformer, I believe, and the welding current is controlled by the windings. I would just like to confirm that this is my problem. The welder runs fine except for the fact that the weld power cannot be adjusted to lower settings, is always putting out too much power no matter where the switch is set. Does someone know how to positively check this "reactor" as a new one is quite expensive. I am a maintenance electrician but just have never dealt with this particular unit. Thanks in advance for any assistance......
Last edited by inillinois2; 10-27-2009 at 08:37 PM. Reason: Link to schematic
Last edited by Thatguy; 10-27-2009 at 06:06 PM.
There is a lot in the circuit besides the reactor ( transformer ) itself. If the reactor was bad, it likely would actually show burned. If it is an open winding, that could be determined with an ohmeter, using the schematic.
Beyond the basic open/shorted resistance measurements, this type of device could only actually be tested in a laboratory environment. However, you should be able to arrive at a decision short of that. Basic VISUAL troubleshooting always is first, and will solve half the cases. Then basic voltage tests on the other components involved. Remember that high voltages are involved, and beyond the visual and ohm readings, this job might best be left to factory service. Of course they will replace major components and send you a large bill!
Is CT1 on the diagram the reactor you referred to? To me it seems to be a current transformer that outputs a signal to PC1.
I can't find the 300w 34 ohm fine adjustment rheostat (R1) on this diagram. Scratch that, it is in the upper left corner and varies the gen. field current.
Basically it looks like a 3Φ weld generator in series with a tapped current limiting inductor Z1 feeding a 3 phase diode bridge. A current transformer CT1 feeds back signals to PC1 and RC1 (which goes who knows where?)
For troubleshooting you might need to simulate a very steady arc, unless you can weld and troubleshoot at the same time. 40v @ 80A is 3200W at 0.5 ohm. You can get a half ohm using a few yards of skinny copper or iron wire but to prevent melting it would have to be submerged in 3 gals. of water or oil.
That's a problem yet to be solved.
What options did you get, if any?
Last edited by Thatguy; 10-28-2009 at 10:24 AM.
Figure 2-4 in your link tells me that the impedance of each of the three sections of Z1 should be 3 ohms at the low welding current setting.
Power off the welder.
Set Z1 to lowest current setting.
Disconnect Z1 and hook a section to a 24 vac transformer (assuming the welder runs at 60 Hz from the generator).
Measure the voltage across and the current through that section.
V/I should equal ~3.
With a 40 VA 'former the output V will probably drop to ~17 vac. Don't leave it on too long.
Repeat for the other two sections.
Last edited by Thatguy; 10-28-2009 at 05:38 PM.
I really have not yet gotten a chance to work on this but did turn welder on myself today. I am confident the reactor is not the problem as i did a visual and i sure did not smell coils burnt. What is going on is that if i have the welder turned all the way down i can still strike an arc. I talked to another of the guys at work and he told me he was using it last week and the welding rod "burnt up".
Tells me it turned a cherry red. I am assuming the welder shorted out. I have a load tester and the generator responds as it should as i ramp up the power, just too much current. I also did a check and the generator is putting out 48 volts phase to phase vice the 42 the print says it should. I do have a Fluke Scopemeter and am as of now going to assume that the welder has blown diodes. Am I on the right track?
Note that VR1/R4 may clip the tops of the waveform if there is no load on the welder.
To check a 275A 300 PIV diode, hook it in series with the 48 vac from your welder and an assembly of a few 100w incandescent lamps in parallel. With the scope you should see half-wave-rectified DC with a peak value of about 67v. You could also use 120vac from your house but with a 300 PIV diode you might be pushing your luck.
The incand. lamps provide current limiting.
A similar diode has a forward voltage drop of 1.3v maximum at rated current and about 1 mA reverse current at 200vdc.
If it is a bad diode, I assume it failed for internal causes and not 'cause it was overstressed, but who knows? These power levels are enormous.
You'll need heat sink compound if you mount a new diode.
Can you post a link to your load tester?
Last edited by Thatguy; 10-29-2009 at 06:05 PM.
With this and a scope we should be able to isolate the problem down to a single component.
(48v/42v)^2 = 1.3 equals 30% more power into the weld, if the arc acts like a resistor, but I don't see how a bad gen can ever put out more power than normal. Maybe R2 or R3 are shorted.
Last edited by Thatguy; 10-30-2009 at 03:09 PM.
I am a Miller Certified Service Technician. A Big 40 is usually a Continental 4 cylinder engine driven welder. All Miller welders produce AC weld output and use a rectifier for DC weld output. The rectifier on one of those is maybe an arrangement of stud diodes mounted on the endplate or more likely a set of diodes mounted in a grid of flat plates as a complete unit. A reactor is a term Miller uses for an AC circuit transformer....if it were used on the DC circuit side they would call it a stabilizer. Bad diodes usually would be low output or no output or sparks flying from a shorted diode. If your output is too hot and will not adjust properly you need to check your fine adjust R-1 rheostat . It is on the control panel and is marked from min to max with numbers. You can use an ohmeter to check it on the backside. If it has 3 wires......check from the center to one side and it should go in one direction ohmwise and from the center to the other wire it will go in the other direction. The values for it are printed right on the side of it. I worked on those all the time in the past but don't recall it being common for one to go to max output. Usually they lose output when that item goes bad. That machine is old school techonolgy...no circuit boards. Normal OCV(open circuit volts) for that machine across the weld output studs is usually about 70-80 volts if I recall right. Another possibility is that someone moved some wires because something came off due to deterioration. All Millers have a circuit drawing on the insde of the machines cover. I have access to all of that at work on my computer via Miller's Extranet........A scope is not going to help you here trust me......I have been repairing electrcial equipment like this for over 15 years........Component test everything first......Little square items with 4 wires are bridge rectifiers and you should have at least one on there. Adjutsable slide resistors are on there as well....2 as I recall. Components must be checked out of the circuit.......means you have to remove some wires to test it and you need to know what your testing and what the values are supposed to be.....I don't usually look at this area of this forum often, but maybe I can help you find the trouble......
Last edited by Rich B; 10-31-2009 at 04:02 AM.
I did not realize you posted a link to the SM......I looked it over. That machine has stud diodes mounted in the end but as I said I doubt that is your probelm. Look at R-1...that is your fine adjust rheostat. Zero to 34 ohms. SR-1 and SR-2 are full wave bridge recitfiers. They are little black square units with 4 wire terminals. One corner is cut with a small diagonal. That is the DC + side. DC - is opposite and the AC's are diagonal from the DC's. They need to be Diode tested......with wires marked and removed. The other adjustable slide ring resistors are probably not your problem but they can be tested as well. Use your parts breakdown to ID each unit and read it's value if it is shown. The print shows all the wire numbers and where they go. All Millers have mostly black wires and they are numbered with white lettering. You can verify what your looking at by using that circuit diagram and checking the wire numbers. I use a Fluke DVM and print out the circuit diagram on 2 pages and tape them together......so my old eys can read them easier.....Check your wiring and the R-1 and the SR's (silicone rectifiers)
Last edited by Rich B; 10-31-2009 at 04:04 AM.
FWIW, each functioning diode takes about 200w from the power delivered to the arc.
By default, from most likely to fail to least likely to fail,
FWIW, I think SR1 & 2 failing by shorting or opening can only reduce the weld output power, by reducing the DC field current to the weld gen.
Last edited by Thatguy; 10-31-2009 at 05:10 PM.
This is a DC only output machine. AC is produced by the alternator and that is the design Miller has used for many years. A similar LINCOLN machine is a generator design and produces straight DC with a segmented commutator on it's armature. A Miller uses a rotor with slip rings and brushes and produces AC. Output is rectified in the main rectifier by the stud diodes (6). Z-1 is the reactor on this machine and since it is before the main rectifier it is AC. Miller sometime confuses things by calling it Z-1 which is usually a DC circuit tranformer used to dampen AC pulses. On this machine Z-1 is the AC reactor and that is their term for an AC transformer. It is a multitap tranformer and responsible for supplying the 5 ranges of weld output. S-3 is the range switch and that is how output is selected from high to low. R-1 is the fine adjust control(34ohm rheostat). It is a wire wound ceramic unit and often goes bad on these older machine. Usually output is lost if it opens or is dirty. Both the range selector switch and the R-1 are mounted on the front panel. Shorted diodes will usually blow open and then power is reduced. If a diode is shorted the machine will act as if it is under a load. The output will be dead shorted the same as welding and the rod sticks. Bad diodes can only reduce ouput not increase it. VR-1 is a very small resistor that dampens the OCV so an arc can be struck a little softer than if it were not across the output circuit. If it is bad OCV will be higher than normal. 95 volts is the Max OCV on these machines.
Here is one important thing that has not been mentioned.....engine speed needs to be checked. If the engine speed is to high output will be high. Engine speed can be tested by way of the AC output using a Fluke meter with frequency or Hz reading capability or an engine meter. Should be 1860 rpm Max no load. Most Millers have a 100hz 120 VAC outlet available while welding. If it has that, that is where you can check engine speed with a HZ meter.100 HZ is the proper number at weld speed for those models. It may have 60hz 120VAC available at that outlet. Either way that is where you can check engine speed. If it is not close to one of those numbers it needs to be...at weld speed....Those old carburetors and engine governors are often a mess.....
The PC board is for the idler control, nothing else. It controls a solenoid that pulls the carb to idle with no load if the switch on the front panel is set for idle.
The more I think about it...the more I think it's an engine speed issue......nothing else on those machines usually makes for to much weld output.......usually to little or none....
Last edited by Rich B; 10-31-2009 at 06:09 PM.