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Roughneck 1 Low Excitation DC Voltage, No Output At All - HELP!

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  • Roughneck 1 Low Excitation DC Voltage, No Output At All - HELP!

    Recently acquired a Roughneck 1f with a 12hp Kohler petrol engine pullstart. Ive been trying to troubleshoot this welder for a couple of days with my limited knowledge and so far my findings are as follows... im getting nothing at all from weld or power on this machine by the way.
    To start off I found the wire coming from behind the flywheel of the engine which im lead to believe if what provides power to the SR2 excitation board. Given that there is only 1 lead coming from the back of the flywheel im of the belief that this is a dc voltage, and I reada positive of between 4-9v DC bouncing around.
    Ive tested voltage at the brushes and nothing at all.
    Ive checked all switches and connections and everything else looks spot on...

  • #2
    Please post your serial number so we can look at the correct diagrams.

    Comment


    • #3
      Roughneck 1f
      hj130197

      Comment


      • #4
        Was this machine sitting unused for a long time? Sounds like it may have lost residual magnetism in the rotating field and needs the field flashed. I think diode D5 is supposed to do that automatically, but if the voltage from the engine is low, or the diode is open, it may not be working as it should.

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        • #5
          Thanks for your replies Aeronca
          am i reading this correctly... is the voltage from the engine coil DC or AC. ITs confusing because isnt board SR2 an arangement of diodes setup to convert AC to DC.
          The machine had sat for some time, but only because it suddenly stopped outputting so im told from the guy who gave it to me.
          I had tested the output from the engine coil wire which is a single wire, thats why i was guessing it must be a DC output. I grounded my meter on the frame and tested the single wire coming from the engines coil and i was getting fluctuating reading from 4-7volts DC. Like i say its confusing as i was aware that generator coils would put out AC, so is there a hidden bridge rectifier somewhere between the engine coil and board SR2.
          Im desperate to get this machine up and running quickly.... Im needing a portable machine to do a job thats come up.

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          • #6
            Best I recall that machine from 15 years back, the wire coming from behind the flywheel taps the ignition coil there and delivers either pulsed or interrupted AC when the magnet passes the coil. That AC goes to a rectifier on a very early board manufactured by Miller Electric long before Miller was bought by Intercontinentalsuprglobal. That line of machines was dropped like hot rocks not long after Miller Electric was bought.

            The board was not available in 2003, and Lloyd a Miller holdover told me no parts were available.

            The board rectified the AC and charged capacitors which activated the exciter. Generally the failure began in the exciter and took out the board.
            Before you invest too much time I suggest verifying the exciter with both an ohmmeter and Megger.

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            • #7
              The board rectified the AC and charged capacitors which activated the exciter. Generally the failure began in the exciter and took out the board.
              Before you invest too much time I suggest verifying the exciter with both an ohmmeter and Megger. [/QUOTE]

              I have a Megger tester... This may sound like a stupid question, but im not an electrical engineer... Where is the Exciter? Can you explain to me pls where the exciter is and how I do this test with Meter and my Megger...
              Im desperate to get this up and running

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              • #8
                For your purpose, the exciter will be the coil of wire wound onto the spinning shaft connected to the engine of the machine

                You need to verify everything from the spinning shaft coils to the board.

                Don't employ the Megger with the board still in circuit!!!!

                Comment


                • #9
                  The exciter is basically the left half of the generator windings on the schematic diagram, along with their associated diodes.

                  I assume you have checked fuse F1 on the circuit board? It's item 54 on page 4 of the parts list.

                  Important question--when you are seeing the pulsing DC voltage from the engine ignition, is the wire still connected to the welder portion of the machine, or is it disconnected from the generator and connected only to the meter?

                  I'm just going to ramble a bit here, I'm looking at the top diagram, Manual Start Model, on page 19 of OM-419. I am not a welder expert, just an old half-brain-dead systems engineer, but bear with me as I ramble. The pulse coil lead from the engine ignition module is only to provide power for the flashing diode (not flashing like a light), but to "flash" the revolving field in the event it has lost residual magnetism from sitting a long time. Really old welders didn't even have this circuit, and you had to start them up and then flash them from a 6V lantern battery, or, if you were really quick, a car battery, (actually the last time I saw this done, car batteries were 6 volts!) but you had to be careful not to burn up the windings, or get scared by the rather large flash it made when you connected--I guess that's why they called it "flashing". Anyway, this should be a positive DC voltage, but it pulses as explained by Franz, and should be stablilzed by capacitor C4. When the engine starts, a small "bootstrap" current should flow from this source through the top (on the diagram) slip ring, through the revolving field, and out the other slip ring to ground. Actually, the electrons flow the other direction, but the result is the same. As soon as that small current gets flowing and the generator is rotating, it will self-excite and start working. If the machine was working, and now won't all of a sudden, it is very unlikely that residual magnetism in the rotating field has been lost, and this circuit should not really matter....unless C4 or D5 are shorted, potentially sorting out the exciter winding.

                  You've probably already done this, but the first thing I would do is be sure the brushes are able to move very freely in their holders, and they are not worn down to the point that the available brush spring tension is inadequate to provide good contact. That is the single most common failure.

                  Next, I would check resistance of the rotating field windings with just an ohmmeter between the two slip rings. You should read some relatively low DC resistance, but I don't know exactly what it should be. I would be looking for an ohm or two, but don't know for sure if that's correct. I wouldn't be surprised at 3 or 4 ohms either. The key is, it should not be zero, and it shouldn't be infinite. DuaneB has posted the numbers for a Bobcat in a thread some time ago, but I don't have time to dig it out, and don't know if it's applicable to your machine or not. Then, you need to check resistance from either, or both, slip rings to the metal shaft of the rotating field to see if a winding is shorted. If you don't read infinity (OL on a digital meter), you have a shorted field winding and your welder is probably junk unless are are going to venture into rewinding the rotor, a pretty formidable task. You could also do this check more thoroughly with a megger as Franz said (be sure the brushes are out and you're only touching a slip ring and the shaft with the probes, or you might fry all the diodes). Again, I don't know specifically what the insulation resistance value should be for that machine. Should be a pretty high value, many hundreds of K ohms or megohms.

                  If the rotor measurements check out, you can also check for a shorted stator winding while you have the meters out. In my mind, a single bad stator winding is not going to affect both power and weld, unless it is the exciter stator. So, I would only worry about that one. FIRST, UNPLUG THE CIRCUIT CARD if you use the megger-- you don't want to toast all the diodes. Then check resistance to ground (chassis) from either wire 3, 12, or 13. Really doesn't matter which one. Again, you are looking for a very high resistance.

                  I would next check the WELD/POWER switch, making sure you see zero ohms between the terminals with wires 2 and 5 with the switch in WELD . Next, check R1, the current control. Put your ohmmeter on wires 5 and 12, and rotate the control from one end to the other. An old analog ohmmeter is really nice for this check, but you can use a digital if that's all you have. it should vary from 0 to 16 ohms (high setting to low setting) as you rotate it, with a smooth change.

                  If all of that checks out, I suspect you have a bad diode on the board or a shorted capacitor. This board is pretty straightforward. You will probably have to unsolder and lift one end of the diodes to check them so you don't get any parallel paths. Do you know how to check diodes with an ohmmeter? If not, I can lead you through it. Also, many digital meters can also check capacitors; just disconnect one end before testing. If your meter doesn't do capacitors, you can check with an ohmmeter to see if they are shorted or badly leaking. If you have an old analog ohmmeter, you can actually see them charge up, which gives some idea that they are not completely failed.

                  Keep us posted!
                  Check PMs.

                  Comment


                  • #10
                    The exciter is basically the left half of the generator windings on the schematic diagram, along with their associated diodes.

                    I assume you have checked fuse F1 on the circuit board? It's item 54 on page 4 of the parts list.

                    Important question--when you are seeing the pulsing DC voltage from the engine ignition, is the wire still connected to the welder portion of the machine, or is it disconnected from the generator and connected only to the meter?

                    Yes the fuse on the circuit board is fine.
                    Ive not seen the schematic, but in guessing this left half of windings shown in the schematic would be representative of the coil within the flywheel. That's the one I tested and I di have everything still in circuit, I hadnrt disconnected anything. I shall disconnect the winding in the morning and retest its output voltage and get back to you folks.
                    Good point... it never dawned on me to disconnect the **** thing from circuit. the wire comes out of the back of the flywheel and its first contact into the machine and circuit is a spade connection into what looks like a large AAA battery which when I tested my tester told me it was a capacitor which shown just under 1uf, which makes sense because the only writing on this thing is 1mf and then a ton of numbers, nothing really to indicate what it is. then it goes out of this small capacitor and into the board as wire no. 9 then following where it goes on the board in circuit it goes thru a bunch of diodes, 4 of them infact numbered D3 D4 D5 D12, which im guessing is the bridge rectifier, so if this is a bridge rectifier shouldn't the input be an AC one from the flywheel coil. I figured four diodes arranged like this are used to convert and AC input source to a DC output one.
                    Check PMs.
                    Can I also just note, Aeronca sent me a PM and requested that I sent him my board for him to troubleshoot and possibly repair FOR ABSOLUTELY NOTHING... Its the first time in as long back as I can remember that someone has offered to do anything for me without it involving them wanting paying for there service. What a lovely lovely fella. If only far more folk were like this in this world.
                    I mean just take a look at this guys replies on this thread, the guy gives a **** what more can i say... Top Top Fella....
                    Last edited by honi; 09-05-2019, 05:34 PM.

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                    • #11
                      You nailed it, buddy.

                      Comment


                      • #12
                        Some misunderstanding on the exciter. The coil on the engine is in the block on the schematic (page 19) labeled "ENGINE IGNITION", and it is not the exciter. The exciter is part of the welding generator itself, further down the page, the windings near the slip rings and the associated diode bridges.
                        The exciter winding on the generator stator is wires 3, 12 and 13. Wires 14,15, 17, and 19 are the power winding, and wires 11 and 16 are the weld windings. What you assumed is quite logical, but unfortunately incorrect. The concept of the exciter in a welder is often confusing, since it seems "excitement" has to come from an outside source. But, that's not generally true so long as there is residual magnetism in the field to jump-start the process. Controlling the exciter current is what controls the strength of the magnetic field in the field windings, as evidenced by the fact that the fine current control on the panel, R1 on the schematic, simply varies the current in the exciter winding as you turn it. Depending upon the design of the generator, that's why some older machines require the current control to be set to max for power--it provides the proper strength of magnetic field to generate the proper line voltage at the plug.

                        No real need to disconnect the wire to test it--I was just wondering if you did, in which case there would be no load on it, and the pulse coil may not be able to actually deliver current, and you wouldn't know. So, you tested it the right way; It is capable of delivering current, and that's what's important.

                        The large "AAA Batttery thing " is indeed a capacitor, probably C4. It is possible it is still bad; when you check the capacitance with a multimeter, it can read OK, but can have high ESR (equivalent series resistance) and therefore not filter very well, but I really can't imagine that would be a big deal in this circuit, and it requires a $60 ESR meter to check it. I doubt that's your problem.

                        As to the diodes, you have two bridge rectifiers, SR1 and SR2. SR1 consists of D1 through D4, and SR2 is made up of D7 through D10. They both get their AC input from stator windings on the generator--SR1 from stator wires 3 and 12, SR3 from the series welding reactor Z, which in turn is fed by wire 11

                        D5 is the flashing diode, and the machine will run fine without it. D12 prevents the flashing voltage from feeding back to the bridges, and it appears D6 is a protection diode - in case one of the bridge diodes fails, it will clamp the positive brush voltage to ground potential instead of letting it go negative---hey--maybe that's shorted! Check it out!

                        As to fixing your board--only reason I could offer that was that it is a very simple board, and requires only an ohmmeter, capacitor checker, and an ESR meter to test. I am not yet set up to test anything more complex in a reasonable amount of time. Still have to build my home-brew design version of a Huntron Tracker to allow testing components efficiently. Even then, complex boards from newer machines are not logical to try to repair without service documents. But buying a tracker is just way more bucks than I am willing to pay, (the capabilities I want start at around $1K and go up from there) and I can probably build an even more capable one with stuff lyiing in my junk box and feed it with an existing function generator and power supplies for virtually no cost. Maybe by spring!

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                        • #13
                          can anyone send me a copy or thenink to the schematice diagram of this machine. it may he me make some sense of whats been talked about as almost everything being recommended here by you kind folks is in reference to whats within this schematic. cheers folks

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                          • #15
                            I done a little testing.. I tested 39.5ohms between both slip rings on my meter... a bit higher than just a couple of ohms, but not high. is this still ok then?
                            i also tried testing betwen each slip ring and the steel rotor shaft. my meter didnt change at all, regardless of what the ohn range setting, i also tried testing on continuity for a short between the windings and the rotor shaft and got nothing.
                            the main large oil filled capacitor tested out fine on my capacitor tester as a 20Uf capacitor, also tested the small AAA sized battery type capacitor which is inline with the engine coil and that shows just unnder 1uf which makes sense because stamped on it is 1mf and a bunch of other numbers. the output from this small capacitor goes out into board SR2 as wire no9 and also another output branching off this small capacitor goes to the large 20uf capacitor.

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