Replies

1. 
   Bob_Doyle | Dec 20, 1998 02:40pm | #1

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   I don't know about the load the machines will draw. I do know you should consider the Makita line of generators. Good machines at about half the cost of Honda.
   I just bought one on the recommendation of gentleman who works on a highway bridge building crew that has hade experience with both manufacturers. The 5700 watt model I bought ran USD1500.00.

2. 
   Guest_ | Dec 20, 1998 07:40pm | #2

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   Bob, I'm a big fan of Honda generators and I'm just about to buy another one. However, I would certainly take a look at something just as good at 1/2 the price. Can you tell me more about the Makitas....What did your friend say exactly.....Where do you buy Makita generators.....How long has he been using them.... Thanks

1. 
   Guest_ | Dec 20, 1998 09:09pm | #3

   *I would suggest buying a smaller generator and a gas compressor. Running a compressor off a generator is hard on the compressor. Generators are not designed for the surge loads imposed by a compressor.

1. 
   Guest_ | Dec 21, 1998 09:50pm | #4

   *Assuming that the compresser runs on 120 volts a 2 1/2 hp motor would draw in excess of 15 amps. I really doubt that it is a real 2 1/2 hp motor but at 15 amps it would draw 1800 watts. It will draw a heckva a lot more on start up which could be a problem as stated in another reply to this post. If you really want to use the generator to power the compresser I would get at least a 10 kw one. Anything smaller will probably end up toasting the compresser motor. A 4500 watt unit will start a 1 hp well pump with no problems. When I tried to start the 1 1/2 hp motor on my milling machine it took an inordinate amount of time for it to come up to speed. I think an air compresser motor would be an even bigger starting load.

3. 
   Lee_Edelberg | Dec 23, 1998 06:43am | #5

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   You don't mention the compressor voltage, so I'll suppose it's 230v (or 240v). The NEC motor-load tables show the full load amperage of a 3hp motor @ 230v to be 17 amps(used for circuit calculations). These values tend to be greater than the actual load of a particular motor.

   There's a guide in the Grainger catalog for generator sizing which recommends figuring a motor starting load at 2 to 3 times it's running load . So a 3-1/2 hp motor would run at about 4,600 watts, double that for starting would be 9,200.

   Lee

1. 
   David_Thomas | Dec 23, 1998 10:04am | #6

   *That 2-3 times nameplate amperage for starting is for induction motors (most all AC motors of any size). I've often been able to start a 2 hp motor on a 5,000 watt generator, sometimes a 2.5 hp motor, sometimes not. Heavy flywheels, crankshafts, etc that need to come up to speed will cause a longer period of high current draw and greater chance of tripping the breaker on the generator. The milling machine mentioned above is a example of trying to get a lot of metal up to a high speed.I've watched the amps and volts of versus tools during startup both on line voltage and generators. Generators always take longer to get a large tool up to speed because both their amps and volts fall off more than power company's lines do.Two tricks that have worked for me:1)Have someone manually hit the throttle linkage on the generator (rev it up) as you turn on the load and 2)(If possible and safe) get the load motor spinning a bit in the correct direction before turning it on (not possible, or at least not safe, with a compressor). Also, of course, don't have your motor working against a load when you start it.An air compressor whose electric motor runs continously (and whose air pump is engaged and disengaged as needed) is better for running off a compressor. Once you get it going, perhaps with an empty reciever, it will keep going. If it has to work with your 3.5hp motor, sight unseen, get a 10kw generator. If you can try your particular load with the generator in question, you may find one between 7kw and 10kw that will work, some combinations work and others don't when you are close to 2-3Xnameplate amperage.You can get a gas-powered compressor for less than a 10 kw generator, a far superior way to compress air, although not as versatile vis a vis your other electrical tools.Or consider a smaller conpressor or even two small compressors. If you don't try to start them at the same time, you can run two 1.5hp motors on a 5-6,000 watt generator. I actually had a 4,000 Coleman generator (US$550) which would consistently run two 1.5hp blowers - by starting them sequentially and using the tricks above.Honda pumps and generators were always the first to be taken from our warehouse to the field because they are so much better starting than Homelite, Coleman, etc. (Also quieter, better in the cold, and twice the price).-David (chemical engineer, owner-builder, and chocolate chef)

4. 
   Guest_ | Dec 23, 1998 10:54am | #7

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   Paul, I see in your post a need to run a 3 1/2 HP motor and a pair of 15
   amp saws! Have the compressor kick on, and have both saws running
   and you'll need 12+KW to begin with. Look for a truck mounted Onan or
   Northern Lights if that's the case. $1000/KW as a rough rule. More for
   Diesel. Explore the option of finding a Mil. Surplus tag-a-long trailer type
   generator set. Could be cheaper. Otherwise, go with the gas engine
   compressor and a 5KW generator for the saws. Do NOT use the auto-
   idle-down feature... you'll burn-up your saw motors.

5. 
   Bob_Doyle | Jan 06, 1999 03:51am | #8

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   I purchased the generator from Western Tool Supply, a chain of stores located in CA, OR, WA, ID. Here is the good "third hand info." He said, a friend of his works as a forman on a highway bridge building crew. His crew uses Makita generators and another crew uses Honda. The crew with the Hondas has to keep an additional unit because there is always one in the repair shop.
   Also, for what its worth, I brought the Makita in to have it converted to propane fuel. The mechanic who does countless conversions on all types was very impressed with the Makita and its Wisconsin Robin engine.

6. 
   Guest_ | Jan 06, 1999 04:15am | #9

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   Bob, Thanks a lot for replying to my question. I'm going to check on these. By the way, I have 38 pieces of equipment with small engines on them. The toughest, best running, and most reliable of all are the ones with Robin engines on them. I never buy a new tool without either a Robin or Honda engine on it, but I prefer the Robins.......

7. 
   dp_ | Jan 06, 1999 07:09am | #10

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   Word of warning on the military surplus generators. They are great...10kw for under 3000 bucks. 10kw uses a 4cyl Diesel, weighs about 1350#. And the 10kw is a continuous duty rating. The drawback: if you look for one, be sure it is 60Hz. There are a lot of the 400Hz units out there. Worthless for what you need.

   DP

1. 
   Russ_Jamison | Jan 06, 1999 07:25am | #11

   *Bob-I'm looking for a backup generator for home use and would like an alternative to gasoline fuel. Do you know if Makita or any other manufacturer make a natural gas fueled generator? What's involved in converting a gasoline generator to propane and what does it cost?Thanks

1. 
   Russ_Jamison | Jan 06, 1999 07:30am | #12

   *Bob-Do know if Makita or any other manufacturer make a natural gas fuel generator? What's involved in converting a gasoline generator to propane and what does it cost?Thanks

1. 
   Bob_Doyle | Jan 07, 1999 10:13am | #13

   *Mine is in the shop right now being converted by a mechanic at Suburban Propane (any big propane provider will have number for you to call.) All thats involved is the installation of a spacer between the carb and air filter, a fuel flow regulator and filter. Materials and installation run about 300.00, parts being little more than half the cost. (I got 2 quotes, the other was for 500.00). To convert it back to gasoline all one has to do is remove the insert (propane venturi) from the spacer.

1. 
   JohnE | Jan 07, 1999 12:07pm | #14

   *Russ;Do not confuse b LPG (liquified petroleum gas, aka propane) fueled units with b NG(natural gas) fueled units.Use gasoline fueled as a baseline. Most LPGconverted units are derated by 5-10%. Most natural gas converted units are derated by 40-50%.Natural gas requires a fixed unit due to the fuel source & the weight to get your required kW output.If you want duel fuel, stay with gasoline & LPGCheers; JE

8. 
   Guest_ | Jan 07, 1999 01:25pm | #15

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   But natural gas is much cheaper than gasoline or propane (half the price) and the gas company brings it right to your house in their piping. We have lots of electrical failures in winter, but when did your pilot lights go out due to loss of N.G? Never happens, N.G. is very reliable, for a fixed location. So if you're on N.G. but subject to prolonged electrical failures (or just want to impress your neighbors with Xmas light show despite a power failure), a fixed N.G. generator is great - but you can't take it with you for the most part. (Compressed natural gas, CNG, is available in some U.S. marinas because lighter than air N.G. is so much safer in a boat then propane or gasoline. But it'd be a pain to find and haul around to job sites.)

   That said, for emergency use only, who cares about fuel costs? But if you used it a lot, you'd come out ahead. I'm toying with the idea of hooking up to N.G. but not electric because at $0.38/therm and a 25% efficient engine/generator (30% would be absolute max possible), I can make electricity at $0.052/kwh versus the electric company's rate of $0.0836/kwh. And if I recover any heat from the generator, I'm even farther ahead. But these projects only make sense for a techno-dweeb gearhead (such as most of us), because a client could never afford the engineering and installation. -David

9. 
   Paul_ | Jan 07, 1999 01:36pm | #16

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   I am curious what size of gas powered Honda generator I would need to power a 3 1/2 horse compressor and a couple of worm-drive skil-saws? Any ideas on how much in Canadian or U.S. funds?