3 phase generator
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  1. #1
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    Is there a 3 phase generator made of roughly 220v and 30-40A cap (6-8 kVA), gasoline or diesel?

    I have already seen the $20K diesel skids of 40kVA capacity that are 3phase only in the Northern catalog, just curious if smaller units were made...

    That said, is there any reason that a rotary converter wouldn't work off a single-phase genset?

    Sorry if I posted in the wrong forum.

    -Matt

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    Matt,

    Two weeks ago I bought a 10kw gas genset from a fellow up in Cleveland, OH. Its a military surplus unit, repainted, new oil and filter, in perfect working order for $1300. He has another one that is available. It puts out 208 3 phase which will work on anything that requires 220 3 phase. Its rated for 35 amps running 3 phase.

    Here is the ebay listing for my generator. He has another exactly like it.

    Generator on Ebay

    Rick

  3. #3
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    Rick

    Thanks for the info but the auction describes a single phase generator (!!)

    How'd you get info otherwise that it was 3 phase?

    -Matt

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    A generator that puts out 208 three phase can sometimes also put out 120v single phase.

  5. #5
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    I have a buddy with a 3 phase Onan that came from one of the plants I work at. It is an older unit and is for sale or swap in central Kansas. Set up for natural gas. Not many hours on it. I can get other specs if you are interested.

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    Hi Matt,
    I have a military surplus generator. It is a two-cylinder, air-cooled, diesel unit rated at 5KW. Actually, by commercial standards, I believe it would be rated at 6.5kw, 26A at 240V. Output is single (120 or 240V)or three (240V) phase. There is a voltage regulator on it and I believe you could adjust it to either 208 or 240 volts, or anywhere in between.
    Once you start it up, you adjust the throttle & rpm to get the correct 60hz output.
    Mine was made in 1992 and has 5000 hours on it. I did some industrial salvage work for a customer and ended up with it as part of the deal. The dealer in Chicago, I believe, informed me that these units typically had a life expectancy of 10,000 hours.
    Overall, it's a really nice unit. I believe there are also similar units available at 10KW ratings. Mine isn't for sale, although all my stuff is for the right price , I just thought you'd be interested in what's out there.
    Good luck with your search.

    John

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    Matt, you could use a RPC on a single phase gen set - but it's probably not feasible as I assume you intend to start and run an induction motor(?)
    You'll need a large gen set (KVA rating) to provide enough 'guts' to allow the motor to accelerate. For a rule of thumb, if your motor is 5HP you'll a gen set of about 30-35HP (about 23kva) to start it. This would actually apply even if you have a 3 phase gen set; but it's worse with a single phase.

    Moreover, you'll need to be sure the gen set is using some form of synchronous generator and not an induction generator. I assume most modern gen sets are synch but make sure.

    So, it's not too great to buy a 30HP gen set just to start a 5HP motor but that's what it would take.

  8. #8
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    I have a couple of old army surplus 5KW continous duty, driven by 4 cylinder gas. Haven't been run in about a zillion years. They are about as big as the old Lincoln welders people used to pull around behind their trucks on axles.
    120, 220, 208, 220 3phase, but no 440 or anything like that.
    Would any of the parts help you out?

    To answer your question, yes they are available.
    Most of the time, I have seen them on the goverment surplus auctions.
    There were some others over in La just a month or two ago.
    Up till a month ago, I had an 8,000 on a welder, but traded it off. Don't think I will ever do anything with the old Army ones.
    David from jax
    (no mistake, they have 3 phase capabilities)

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    It says in the E-bay ad that it is single phase. ???

    Think Snow Eh!
    Ox

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    Buddy of mine has an Onan of that description, he uses it down on his farm. They should be available still, even if the 200 hour life single phase Y2K specials seem to have flooded the market.

  11. #11
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    Matt a 3 phase gen set will be around 20 kw if you have one that will make 40 amps 240 volt
    ie... 40 x 240 x 1.73(this is the factor to account for the 3 phase ampage) 40 x 240 = 9600x 1.73=16,608 watts/.8 powerfactor=21 kva
    If your need is full time the military air cooled 3600rpm gen sets are junk. The plants are over 30 years old, no parts, drink gas at 2 gal/hr and have a poor voltage reg to start motors. Thay are fine for short time use but if you need a good set find a Lister or duetz gen set with the air cooled diesel, or a military plant with a watercooled 1800 rpm unit. Thay show up on ebay from time to time at a good price....Phil in Mt

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    Onan made generators that were used for standby power that could be wired for single or three phase power with voltage up to 600 volts. I have one that is set up for single phase as standby for my house. They had several KW ratings. They were powered by a 4 cylinder engine that would run on natural gas, propane or gasoline. Good ones with low hours are selling for $2000+. I have seen a few on ebay.

    Joe

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    First, spend some time brousing the web or ebay to see what is out there.

    Most 3 phase generators are 12 lead reconnectable. If they are 12 lead, they can be set for 240v single or 208, 240, or 480 three phase. Any 3 phase generator will run single phase without reconnecting, but with only about 1/3 capacity.

    There are some really stout 15 kw 1200 rpm 3 phase units with 2-71 2 cycle Detroits. They are off railroad refridgerator cars. The good thing about 2 cycle Detroits is they can burn a diet of at least 30% used engine oil or other flamable oil. (NO synthetics). I don't know what the maximum percentage of used oil is, maybe someone else has experience.

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    Kohler makes a nice line of 3 phase and 1 phase generators rated 6.5KW. The single phase are rated to start a 4 HP induction motor. Will guess the 3 phase may have a motor-start higher rating.

    As mentioned above, the larger Kohlers are typically 12 lead and can be field-reconnected for 1 phase or 3 phase output. I don't know if the 6.5 is that way.

    Bob

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    Hi Matt,
    I wanted to follow up on with some more information and a users perspective of the generator described in my previous post.

    This unit is skid mounted, approximately 51"LX31"W and weighs about 1000 lbs fueled. It's also rated at 26A for the 240V single phase, I don't remember it's 3-P amp rating. It is also an 1800 rpm unit, electric start, and starts on a 24V battery system. I'm not sure of the fuel tank capacity, but looks to be between 5 and 10 gallons.

    One day, I wanted to run it long enough to burn up the fuel and refill with fresh diesel. Of course, with no load it isn't doing any work and just sips fuel. After four hours and no noticeable change on the fuel level gage, I started loading it. My shop is wired so that I can disconnect from the outside world and plug the entire shop into the generator.

    First off I started my 5 hp RPC (it had the wrap cord around shaft, pull cord, and throw switch, starting system). Then I turned on my 3hp mill, 3/4hp lathe, 1/3hp drill press, 1hp T&C grinder, all are three phase. Then I turned on all the lights in the shop (1kw) and turned on the 1/2hp and 1hp pedastal grinders. Granted, all of these machines are spinning free without doing any work. At this point, I had the generator running at half it's rated load. An hour later, the fuel gage had dropped by 1/8 a tank and I gave up, deciding the fuel in the tank was just fine.

    The 3hp mill didn't start as snappy as it does on line power, but it wasn't bad. I think if you slowed a vari-speed system down before turning it off, you could restart it on a smaller generator, since it's "geared down".

    One other time, I was testing a 6X18" surface grinder, don't remember the motor size, but probably 1hp. The generator was hooked up 3-P directly to the grinder. The grinder started right up and ran fine.
    However, imagine a grinding cycle. The table reciprocates beneath the grinding wheel. During each pass, the motor momentarily requires additional amps for the grind, then it runs free until the next pass. In practice, at every pass, the additional amp draw made the generator surge to meet the demand. By the time the mechanical system, "governor" responded to the electrical demand, the grinding pass had already been completed and the demand removed.

    The result of this situation is a perceivable slowing of the grinding wheel during each grind pass and a loping generator trying to keep up with the intermittent demand, but not reacting fast enough. It worked ok for our testing purposes, but I don't think this is a good situation. I don't know how powerful the generator has to be before this "surging" would not be noticable.

    Hopefully, my experiences will give you some insight in choosing the best generator for your own shop.

    John

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    would a fairly large flywheel inbetween the motor and the generator take care of the starting issues? It seems like it should, but I don't know much about this stuff.

    -Justin

  17. #17
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    If you check with some of the dealers who sell US Government surplus equipment, I think you will find a number of Onan diesel gensets of about 5 to 10 Kva, connectable for three phase power. These have an Onan air-cooled two cylinder engine. Not a particularly long-lived engine and somewhat problematic from what I have heard.

    The telephone companies had a number of diesel gensets for standby power that were removed and dumped into the used equipment market a few years back. these were often Onan sets, or even older sets with Hercules engines.They were about 12-15 Kva on the smaller end of what was avaialbe. They had mainly "exercise time" on them and were wel maintained.

    If you get a paper like "Rock and Dirt" or "Construction bargaineer" or "Boats and harbors", you may find some ex-military or ex phone company gensets for sale. Be careful as to how low the ratign is on the generator you get. Motor starting creates quite an inrush current. Simply matching the amperage on a motor's nameplate to the amperage on a generator's nameplate is not a valid means of determing the required size fo a generator. The inrush current on a motor with a nominal amperage rating significantly smaller than that of the generator power it can actually collapse the voltage in the generator. Motor starting current vs. running current are two different things. You have to get a bigger generator than what your motors require to cover the starting current and keep up the voltage.

    I think most of the smaller Military gensets were reconnectable for a couple of voltages and single and three phase. I say this as we have an 18.5 Kva ex-military diesel genset. We needed a three-phase diesel genset to power the machine tools used for a steam locomotive restoration project. Being on almost no budget, this meant looking hard. On a back road, I found an ex-military diesel genset sitting in a country machine shop's junkyard. It was about the size of a 300 amp engine driven welder. After determining it was for sale and getting permission to look it over, I found it was rated at 18.5 Kva. What made the generator quite interesting is that it was reconnectable for single or three phase power.

    The 18.5 Kva set has a Marathon Electric generator with brush type exciter and mechanical voltage regulator. The engine is a Continental 4 cylinder diesel, running at 1200 rpm synchronous speed. It was built in 1951.

    My buddy bought the genset for 1200 dollars and we put it to work. We connected it for 208 3 phase power and used it to run a few machine tools. It could just start a Reed & Prentice Engine Lathe with 10 HP motor.

    As we got a few bigger machine tools at the locomotive project, the 18.5 Kva set simply did not have the motor starting capabilities. This time, I spotted a bigger diesel genset sitting derelict at the side of a quarry. I made inquiry and was told to go look it over. The genset turned out to be driven by a Murphy Diesel Engine (made in Milwaukee for marine, stationary and crane power). The generator was made by E-M. The generator panel was destroyed. From what I could find out, the Murphy diesel genset was only about 55 years old. The quarry operators said their master mechanic took a couple of diesel batteries and started it once or twice a year and made sure it had good antifreeze in it. Aside from that, it had sat unused for 30 years. The quarry operators said they were in foreclosure, so if we wanted that genset for our locomotive project, we could have it. I meggered the generator and it was surprisingly OK despite being an open frame machine and sitting under just a tin roof for 30 years. We hauled that Murphy genset back to our site, and had to retrofit a solid-state voltage regulator onto the generator. E-M, as a generator builder, is defunct and absorbed by another firm. They sent me what information they could, including a wiring diagram for the original mechanical voltage regulator. No data plate on the generator was left intact, so the guestimate is this is a 100 Kva set. It is overkill for what we do, but the price was right. We can start every machine tool we have and take simultaneous hogging cuts without that old Murphy breathing hard.

    The downside to any of these old gensets is likely to be parts and service manuals. The 18.5 Kva set has a Continental engine which the latest incarnation of Continental (WisCon) claims no knowledge of. Thus far, the old Continental seems to run OK, but we have no idea of its maintainence history. The filters were the old cartrdige style, and it took a little doing to match up replacement filter elements. Luckily, the Military had a full wiring diagram put on a plate inside the genset cabinet as we did have to troubleshoot the mechanical voltage regulator wiring.

    If you buy an ex-Military genset of any age, or any older genset (such as out old Murphy diesel), you may well find yourself on your own when it comes to cross-matching filters and parts or for repairs and service. Onan was absorbed by Cummins a few years back, so I do not know how well they would support the older Onan ex-military gensets. If you can get an ex-Military genset for the right price and it is intact, you will be getting a very well made unit which is way overbuilt by today's standards. OTOH, if it is an older genset, it may have a mechanical voltage regulator for the generator (these were used intot he early 1970's). Mechanical voltage regulators are very sensitive little devices. if one of them goes south, be prepared to retrofit a modern solid state voltage regulator. Otherwise, an ex-miltiary set will have more than enough copper and iron for the nameplate rating and will be rugged set.

  18. #18
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    A little warning about gen sets like that.

    When running they use a little more than a half a pound of fuel per horepower hour. You're gonna put some gas through that thing.

    The engine in the illustration looks to be an opposed four cylinder air cooled engine. If it runs at 3,600 RPM it will have to come down for overhaul probably before 2,000 hours. That is considering land based operation, airplane engines of that type come down at 1200 hours.

  19. #19
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    We have a 3 phase Warner & Swasey engine generator plant. circa. 1958, Put together for what was the Department of Commerce, Civil Aeronautical Divisin which is now FAA and under Department of Transportation. Runs on propane. Continental 6-Cylinder, 37.5 KVA,120/240, Generator was built by EM (electric machines co.) We got it running but scared to mess with the electrical part without proper manuals for safe operational procedures. Can't find manuals anywhere? Don't know what we'll do with it. May just run a couple ranches around here in North Florida.


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