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  • 200 airpak diesel

    Hello folks

    I bought a Bobcat 200 air pak diesel. I am disappointed that the speed of the engine is not completely variable. The auto throttle is on \ off. When using the generator the engine runs at 3600rpm even with a very small load. The design is rather oridary. I expected the low torque of the diesel engine to be exploited. But not ... Do you know if the software can be calibrated otherwise?

  • #2
    I'm guessing that the 3600 RPM has to do with providing 60Hz power rather than how much load is on the generator. If it ran down at 2400 RPM, the power would be at 40Hz and all sorts of other problems would ensue.

    Maybe if the machine was inverter based this would be possible, albeit at an efficiency penalty.


    • #3
      Egg Zackery Fix.

      3600, 1800, 1200 and 900 rpm = 60hz

      Slower they turn more expensive they get to build.

      Inverter types like Honda get real expensive real fast.


      • #4
        Yep-I'll second the comments by Fix and Franz. Great summaries in a few words. It's all about designing and building to a price point.


        • #5
          Ok I understand but the output of the welder is inverter based. Before having the bobcat I had a honda inverter. So I'm pretty disappointed in the generator function of the bobcat. Is it possible to add the option of excel outlet? Another thing that tells me that it is inverter based is that when I plug in a cellphone charger for example, the motor stays at 2400rpm and it works.

          Thanks guys


          • #6
            Looking at the schematic of the newest serial number, The welder is inverter based, however the welder gets it's power from the generator which is a simple electromechanical machine so RPM = frequency.

            A cell phone charger plugged into one of the generator outlets is not likely enough of a draw (through CT1 and into PC3 Main Control Board) to trigger the engine to kick up off the 2400 RPM idle. A cell phone charger will take in almost anything "AC" and spit out 5v dc to charge a phone. I'd bet that if you took your multimeter and looked at the A/C frequency on the 120v outlets at 2400 RPM, you'd find that it's 40Hz instead of 60Hz when its at 3600 RPM.

            I'm not sure what an "excel outlet" is - could you explain?

            Are you still within the return period on this machine? I can understand being disappointed, however if this was your expectation/requirement, it would be pretty easy to determine that this machine wouldn't meet that before you bought it. It just does not have the hardware to perform like you want it to - no amount of reprogramming can fix missing hardware .


            • #7
              If you have a meter than can measure frequency, I'd be really interested to see if Fix Until Broke is correct. I think he is, and I agree with him, but would really like to verify, just for knowin'.


              • #8
                Not allowing for magnetic slip in a 2 pole alternator it's 48hz output.
                Allow for slip 46-47 is realistic.

                The joy of low cost based on ignorance and shine is oft forgotten when performance is viewed.
                Reminds me of a beer factory where many machines had update kits and speed improvement kits and BREAKDOWNS that more than compensated for increased product output.


                • #9
                  Franz, you are an amazing guy. First person I ever met outside of an engineering environment who even knew there was such a thing as magnetic slip.


                  • #10
                    Fix and Franz you're right. At 2400 rpm I have 40hz and exactly 60.00hz at 3600. I thought this new model was going to be much more techonologically advanced. At $ 15000 Canadian I was expecting more.
                    The excel outlet is a plug some machine have. It gives A \ C power at idle.


                    • #11
                      Far be it from me to criticize young women recently graduated from Enginincompoop School working to balance a BIG company EEOC chart till they can find a fool to marry who will pay their student loan, but it looks to me like the excel thing is another of the long series of "we really screwed that, lets call the fix an accessory" and hope for bonuses.

                      In the age of digital electronics inputting 40hz and pulling 60hz out of a box is probably a walk in the park, and a good income product for a company thatmisrepresented a machine, not that I'm saying Supergianttransglobal and ocean front would ever do such.
                      He!! America consumed train loads plus ship loads of 60hz power that left generators as 25hz power. Probably still a few stations making 25hz and converting it.

                      I wouldn't be shocked if some old Revenue Cutter rider could find a plan and sell kits to make the boxes.

                      You want something to be disappointed aboot(C) consider the additional piston trips to idle that machine at 2400rpm. At 1800 it could produce 30hz electrons and my thinking is a doubler would be easy to build to deliver 60hz. As the situation stands, you gotta convert whatever frequency to DC and then convert that DC to a stable 60hz just like Honda does. It's almost building one of them inverturd welders.


                      • #12
                        Just for everyone's knowledge leveling - "Excel" seems to be a miller only option on the Trailblazers


                        Originally posted by Miller Website
                        Excel™ power (option) Power at idle — a Miller exclusive. Unlike competitive machines that provide auxiliary power only at 3,600 rpm (max), Excel power delivers a full 2,400 watts (20 A) of 120-volt inverter-based, pure sine wave power at 2,400 rpm while not welding. With Excel power you can operate jobsite tools like grinders at quiet, fuel-saving speeds. Refueling time and operating costs are reduced with Excel power, which means more productivity and profitability. Plus everyone on the jobsite gets a better working environment because noise levels and exhaust emissions are lowered. Excel power — available only from Miller.
                        My take on it is a bit different than Franz's though. It might be that the Excel option is an efficient way to idle the engine and still provide clean 60Hz power for lower power requirements while retaining the energy and cost efficient, not to mention reliable, method to deliver full power capability of a traditional electro-mechanical machine.

                        The welding side of the Trailblazer looks to be full inverter which explains why it can run at a variety of RPM's

                        Originally posted by Miller Website
                        Weld Speed Auto-Speed™ 1,800, 2,400, 2,800, 3,200 or 3,600 rpm


                        • #13
                          As Franz and Fix already said earlier, frequency at a give RPM is simply based upon the number of poles in the generator. Add more poles (more complex core material, more complex wiring, potentially more rotor balance concerns, higher labor costs....all that stuff), and the engine can run slower, as has already been noted. 2 poles must rotate at 3600 RPM to get 60 hz. If you buy an industrial quality generator, like a high-priced Onan (Cummins), Kohler, etc, it will have 4 poles and run at 1800 to get 60 Hz. Put in 6 poles, and you can run it at 1200. Etc. So why so few poles? Cost. And, the saga continues to include engine power and torque curves. It takes something like an old Caterpillar RD6, huge bore, long stroke, lots of iron to generate a lot of torque at low RPM, and the required horsepower. Cool explanatory video.

                          Check the torque and power curves on car engines today as opposed the past. Make 'em small, turn 'em fast, get lots of power and torque, and it's way cheaper to build. Less iron (or aluminum), easier to move around on the plant floor during production, lower materials cost, less weight to pay to transport during the build process and delivery to dealers..... So, which of these things would drive a generator (or welder) manufacturer to build a slower turning conventional machine? More costly generator to build? Larger, heavier engine? Just no incentive. Oh, wait, people are complaining about the noise and potential wear? Well, I'm guessing it is now becoming cheaper to rectify power from whatever frequency that results from whatever speed you want to turn it at, and put in an all-electronic inverter, perhaps procured from a subcontractor who can generate economy of scale--not always, but I'd bet often. And for the engine, as oil has dramatically improved and it has become cost effective to hold ever-tighter tolerance when building it....the thought is it will last as long as the old, heavy, slow ones. And they do. I remember when a car with 100K miles was considered junk. As Franz said, that's how you do it now, because it's easy and comparatively cheap when you look at the big picture. So, at the bottom line, other than "environmental considerations", a manufacturer has absolutely no incentive to build a slower-turning machine. And, if they can still get 15K Canadian for a Bobcat, where's the problem, from their viewpoint? An ugly and unpleasant truth.

                          As to the 25 Hz applications, works fine when you aren't much worried about weight....transformers are WAY heaver for the same power capacity at 25 Hz as opposed to 60 Hz. Inductive reactance, one of the key transformer design parameters, = 2 pi * frequency * inductance of the coil, which is related to wire size, number of turns, core material, etc. For a given inductive reactance value, cut the frequency in half, and you have to double the inductance to get the same result. More wire, more core material, more weight. I can't think of any transformer design equation that gets better results at lower frequencies. That's why airplanes use 400 Hz--much, much smaller electronics packages, and if you've ever worked around airplane design, there are weight budgets for every single thing from the engines to the potty. Exceeding your budget will bring down substantial wrath from above, because it translates into reduced range and reduced lifting capacity. So, as much as I hate it, when I need 60 Hz power from my Trailblazer, it's screaming at 3600 RPM.

                          I know they converted 25 Hz to 60 Hz, but have not researched how they did it. I suspect it was rotary converters, similar to what you might do to run a 3-phase machine at home with only single-phase power, but I don't know.

                          Rambling complete.


                          • #14
                            25 was a wonderful frequency, easy to make with hydro turbines given the quality of machining they had in 1920. Bear in mind those old spinners were wound with cotton covered varnished magnet wire because that was state of the art. Interesting coincidence, municipal electric and electric welding are about the same age. First muni systems evolved from Electric Railways running small steam plants and hydros where available. First Hydro muni here was generated by the Genesee river as DC. Even with Edison Cable you can only deliver DC about a mile, so the rail systems built bigger dams and 25hz machines. Converter stations every few miles with a man turning the MG set on and off.

                            Muni here began as a shared venture between an interurban and an investor group with rights to river power and grew from there. 25 allowed power beyond center of the city, and was actually easy to sinc with additional stations. Many industrial users still made their own electric. 1926 the PoCo challenge anyone to make power cheaper for 30 straight days than they could buy it. Only 1 customer won a free supply of coal in that and the PoCo gained customers. With better wire insulation 50 and 60hz became easily possible and smaller spinning generators produced more electrons. The US settled on 60hz, and converters got installed to keep 25hz stations pumping into the system during the Depression.

                            Converter is just a vertical M/G set with a drop dead ball below the bottom bearing, just in case a bearing fails. Hopefully it keeps the machine from a total crash.