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Building a generator

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  • Building a generator

    Hello folks,

    I usually just lurk around on this site, hope it's not considered rude to just pop in and ask a question. If so just pitch me out.
    Anyway I have aquired what I believe is a "belt driven generator" It is a Dayton but apparently old enough that the model numbers don't coincide with anything at Graingers.
    It's specs are 20000 watts. 83.3 amps and is to be driven at 3600 RPM.
    The tag on it indicates that it was tested/rebuilt in 1983 and the plastic put on the shaft to mask for painting is still there. I've toyed with the idea of running a generator off my tractor PTO so I grabbed this thing when it was offered.We live out in the country and power outages are not uncommon. Thought maybe I could build this thing into a little shed and just back the tractor up, hook up and get the lights back on.
    I have seen PTO generators that seem to have some type of transmission. I'm thinking I'd have to build some sort of gear drive to get from 540 rpm to the 3600 needed.
    The tractor has 26.9 HP at the pto shaft.
    I know this isn't a direct machining topic but I've seen similar projects posted here and you folks seem to be in the know about this type of thing.
    So I'm hoping some of you will help an old carpenter out and comment on how you'd approach a project like this.


  • #2
    You could make a chain driven set up with some large sprockets and chain, some plate and bearings.

    knowing how Inventive farmers can be you might already have the stuff sitting around to use now.

    Make a trip to the junk yard and find the more expensize parts as cheap as possible and build down from there.


    • #3
      Get your neighbors to help you! When they see your place lit up like Christmas they'll all be over to borrow some power Make'em earn it up front...
      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

      It is true, there is nothing free about freedom, don't be so quick to give it away.


      • #4
        Look around for a gearbox specifically designed to do the step up. Graninger and others sold em.

        If you can find such, I suggest you run with a timing belt drive. I believe you will have a practical machine.

        Step the 540 up to 3600 with a 6.666/ ratio, - - -
        Well, whatever you can find slightly over that.

        Just a SWAG but you may get 18 kw plus or minus a bit.

        Suggest you use a minimum of two stage step up.

        Avoid a wild over-hung load moment on the input shaft.

        Good luck Ag


        • #5
          Agrip has some good advice, a timing belt has many advantages. Long life, no chain case, no lube, light weight.
          Have a look at the generator section at this site for more info on setting up your gen head.
          Welcome aboard I'm sure you will enjoy the circus.
          Home, down in the valley behind the Red Angus
          Bad Decisions Make Good Stories​

          Location: British Columbia


          • #6
            I just finished building an emergency generator a couple weeks ago. It has a 10KW generator head (Harbor Freight) that supposedly wants to see 20HP to run at maximum output. If you only have about 27HP you might not be able to run yours at full power, but you still will have a whole bunch of power that you would not otherwise have.

            In my case I am running it with an engine from an 87 Honda CRX. Welded up a frame to mount engine, gas tank, generator and other assorted parts. Threw away the transmission but saved the input shaft. Turned off the case hardened gear teeth so as to mount a dual “V” belt pulley to drive the generator. Probably would have been easier to make a new shaft from scratch, but at least it had the “correct” splines to match the clutch. Got the pulleys from “Surplus Center” and they give about a 2:1 setup. Thus engine runs at a quiet 2000 RPM.

            Got a change to test it last Thursday. Had the dogs out for what they consider to be their mandatory afternoon walk, it was overcast and just starting to rain. Get them back in the house and sit down for about 5 maybe 10 minutes before noticing “boy” its really dark outside. About then I also noticed that we had lost power. So I step into the garage to have a look, and its raining like hell leaves and small branches everywhere, across the street the neighbor has three trees down. Well not quite down one was resting on the roof of his front porch. These were 12-14” diameter and broken off at the base. Behind him more trees are down. The neighbor to the right of me also has two trees down. I lost one branch on one tree.

            With heavy rain and no power to run the sump pumps my basement will flood rather quickly, as my shop is in the basement this is not acceptable. Start generator and connect to sump pumps, freezers, and refrigerator. Neighbor to left of me brings over an extension cord to run his sump pumps.

            Rained on and off for the next couple days, flooding and downed trees taking out power line all over the area, the power company was totally overwhelmed. Power was not restored until Sunday morning.

            With the exception of a minor tweaking to the speed control governor the generator ran flawlessly the whole time.


            • #7
              Mad Scientist it sounds like it has already saved you from losing your shop and food in the freezer.

              If my power went down I would be screwed, I would have to go buy dry ice to keep the freezer cold. A half a beef rotting away would piss me off.

              A generator is on the TO DO list now.


              • #8
                I'm just finishing putting together a small one right now. I'll post some pics when I have it running.

                As for running that monster alternator the original poster has, run it through a standard automotive transmission backward. Transmissions have to work in both directions. To get the 6.6 to 1 ratio a truck transmission will be needed. Current Chrysler six speed manual light truck transmissions are around 6.3 to 1 in first gear which should be close enough.
                Free software for calculating bolt circles and similar: Click Here


                • #9
                  An NV 4500 has a 6.34 to 1 first gear and can be found in 1 ton chevy and dodge trucks. You could also find a 4x4 with a low range transfercase. using the t-case and engine you could get well below 6.6 to 1 and you can probly find something pretty cheap complete and running. S10 blazer, Bronco II, sidekick, Samurai. any would work.



                  • #10
                    Generator packaging

                    Power losses are sky high for any speed inducer, plus to rig a heavy transmission backwards, connecting your generator to a PTO or whatever, might be a real eyesore. LOL. For PTO operation, power band belt would require a 20 inch or so pully, driving a 3 incher on the input to the generator. Old Onan 6.5 KW generators utilized 11 HP, so your PTO would be maxed out at probably less than 12 KW of load.

                    Homebuilt aircraft builders prefer Subaru liquid cooled boxer engines over VW aircooled engines. Plenty available, and cheap, from the pickapart yards. Standard of 4,000 rpms for the homebuilts, into a vbelt reducer for a sensible prop speed. Only requirement would be to fab a flex connector to the Subaru flywheel, connecting it to your generator input shaft. Add radiator, muffler and fuel tank, and make popcorn. Subaru: Less than 166 lbs weight, up to continuous 170 HP. Parts available at NAPA.



                    • #11
                      I built several of those using the Harbor Freight 10kw. Pictures are posted in the completed projects section at


                      • #12

                        Wow! Didn't expect this much response.
                        You guys have planted many seeds in my noggin.
                        Car motors, truck trannys.
                        I'm off to see these pictures you've sent me to
                        Many Thanks


                        • #13
                          What rpm does the tractor engine run at? If the pto is spec'd for 540 rpm, it must be related to a typical engine operating rpm. Could it he 3600- if so I'd be looking for a way to rig up a direct drive, even if it had to come from the front of the engine. Another way of looking at it is to check the operating parameters of the engine. At what rpm is the rated power achieved? If the direct drive rpm can be about right, you can avoid the hassles that come with that much of a step up that is required off your pto.

                          I'd have to say that realistically, you'd be able to get 10-12 kw from that generator if run from the tractor engine. I don't think you'd be wanting to run it steadily at much more than half its power rating,

                          My next thought on this is to rig up some kind of governer so the system can come close to maintaining frequency. I don't mean close enough to keep a clock running in perfect time, just good enough to avoid having trouble with 60 Hz motors, etc.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                          • #14
                            I have to agree with the Subaru boxer engine idea and it is one I've also seriously considered. It has the additional advantage of providing a lot of waste heat to warm the building as well as providing electrical power. Get one with a cruise control and you can manage the engine speed, too. A Mazda rotary engine is also one to consider. An optional natural gas conversion might be a plus, too.

                            They have enough HP to drive twin generators so you can sell your excess to your neighbors


                            • #15
                              Originally posted by Evan
                              I'm just finishing putting together a small one right now. I'll post some pics when I have it running.

                              As for running that monster alternator the original poster has, run it through a standard automotive transmission backward. Transmissions have to work in both directions. To get the 6.6 to 1 ratio a truck transmission will be needed. Current Chrysler six speed manual light truck transmissions are around 6.3 to 1 in first gear which should be close enough.
                              Thats why a trip though the junk yard should be first and engineer around that, A truck tyranny would be a solid and reliable way to do exactly what he needs at a low cost.