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2Dogs
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# Posted: 22 Mar 2011 05:24pm
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Help. I'm having trouble sizing a genny. I need the smallest genny that will power my biggest tool. The genny will be used to run my power tools and top off my batteries if needed.
I have written the tool manufacturer but cannot get an answer from them. What I need are the starting amps.
The tool is a DeWalt 746 table saw. It is 1 3/4 hp 15 amp 120v. It has an induction motor. Code G
Every table I have read on motor starting amps says a 1 1/2 hp motor should be 4200 to 4900 watts to start. I would rather have a smaller genny than that if possible.
I borrowed a friends Honda 3000 Handi inverter generator and it started and ran the saw just fine but I don't want to spend$2500 on a genny. $1000 is about tops.
The mortor manufacturer ( Marathon) is no help either they say talk to DeWalt.
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Steve961
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# Posted: 22 Mar 2011 05:59pm
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A Honda eu2000i is rated for 16.7 amps and should be able to handle a 15 amp table saw. It's light weight, fuel efficient, quiet, and costs around 1K. It's one of the more highly regarded generators in it's class.
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MtnDon
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# Posted: 22 Mar 2011 06:28pm
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One of the worst things is an undersized generator. It is hard on both the generator and the motor it is trying to start. Both will have a short service life if the generator is undersized.
Unfortunately starting power is something that is not usually easy to find. One reason the motor manufacturer handed you off to the saw manufacturer is the motor guys have no control over whether or not the saw guys are using a motor that is marginal for it's use. Many variables.
My guess is that the 2000 watt generator will be too marginal, but it is only a guess. Is there a tool rental place, maybe you can rent one to try. Or maybe a Honda dealer has a demo. Here one of the dealers has a couple they use themselves and are usually agreeable to let someone bring in a tool or whatever and give it a test. If it works then it makes sense to buy the genny from them even if it costs more than on some website.
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bobrok
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# Posted: 22 Mar 2011 06:52pm
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Quoting: Steve961 A Honda eu2000i is rated for 16.7 amps and should be able to handle a 15 amp table saw
Quoting: MtnDon My guess is that the 2000 watt generator will be too marginal, but it is only a guess
I'm going out on a limb here and ask you both about this. I know the rating is 16.7 amps but is this starting amps maximum output or continuous output? I have one of these eu2000i's and an old Craftsman table saw rated at about 7 amps. The green overload light flashed briefly once or twice, but not always, on startup last summer. Once the saw was running, of course, there was no problem whatsoever. But I have to question the startup draw of even my small 7 amp rated motor.
I wish I knew more about electric/current. What do you think?
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Erins#1Mom
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# Posted: 22 Mar 2011 06:53pm
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While wondering through the campgrounds at BMS last weekend, I was suprised at the number of campfuls and RVs using the Honda 2000.
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MtnDon
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# Posted: 22 Mar 2011 07:32pm - Edited by: MtnDon
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The amps on the label / name plate is operating amps, the amps being drawn as the motor does the work it is rated for. For example I have a Dewalt grinder. The name plate states 5 amps. When started the Kill-A-Watt meter jumps to 8 amps then falls to 2.5 or thereabouts while the motor runs under no load. When the grinding wheel is applied to steel the amps goes up and readily reaches the 5 amps on the name plate.
The same thing will happen with a motor on a table saw; a high peak as it starts, then as the motor speed stabilizes the current draw will settle down to a lower value as well. That will be lower than the rating when the saw is running under no load. The current draw will increase as it is cutting. Try to force a large piece of oak into a dull blade and the power draw will go up again, maybe even higher than the start current and pop the breaker.
Generators have a continuous rating and a maximum rating. The EU2000 is rated at 1600 watts (continuous) and 2000 maximum. That 16.7 amps is the max; 13.3 is the continuous rating.
Unfortunately the number that is prominently displayed on a generator is almost always the maximum, short time or peak. I've seen some small generator called 2000 watts rated at only 1400 continuous.
So if that saw that started this thread has a 15 amp rated motor, when working, say ripping some 2x stock, it could be drawing more power than the continuous rating of the EU2000. So I remain reasonably certain that starting it will be overstressing the generator until the motor reaches full speed. That will cause unwanted motor heating and possibly overheating the alternator in the EU2000; possibly causing the voltage to drop, which in turn will place more stress on starting the motor.
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BlaineHill
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# Posted: 22 Mar 2011 07:35pm
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You are right to be concerned about the start up amps. That is really the limiting factor. The resistance in the motor can be almost a direct short on start-up. I was able to power my 1 HP air compressor with a 4000W peak/3500 continuous generator, but I think I am on the hairy edge. Air compressors are notorious for huge start-up current -- my 1-HP compressor probably pulls 35 to 50 amps to get going and air compressor manufacturers don't reccommend trying to run from generators. If you are wondering why it does not trip a 15A or 20A breaker in the house when you turn on your saw it is because the current drops back down to reasonable levels before the breakers can react (but the massive current will cause a voltage drop dimming your lights for half a second!).
I guess my tip would be trial and error to match the generator to the equipment. If you get in a spot where the tool hesitates, pulse the tool under no load conditions to get it spinning and allow the generator to [possibly] increase RPMs before going all-in.
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Just
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# Posted: 22 Mar 2011 07:40pm
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I hoped Don would tag this thread , He is the goto guy here for juice quiryes ,, yes Father!!!
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Gary O
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# Posted: 22 Mar 2011 07:47pm - Edited by: Gary O
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Quoting: Just I hoped Don would tag this thread , He is the goto guy here for juice quiryes ,, yes Father!!!
Boy he sure is
I whipped out my manual of my 3000 watt 'Chicago' jenny from HFT and nothing, however there was a handy chart riveted to the display shelf at HFT that was pretty straight forward.
The info is out there.
BTW this one was $400 and has done it all for me, but I sure shut it down when not using a power tool, just to hear myself think (get what you pay for)
it is 4 stoke however
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bobrok
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# Posted: 22 Mar 2011 07:53pm
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Thank you all. This is great. I was going to say 13 amps on the Honda but I don't have it here and didn't want to misspeak. The other thing was pulsing the motor. I instinctively have done this when operating my saw on the Honda...don't know why but it seemed a reasonable thing to do.
You guys are great and this forum rocks!!!
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MtnDon
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# Posted: 22 Mar 2011 08:04pm - Edited by: MtnDon
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Compressors are about the worst thing to start. Other tools that are hard starters are things like my high speed shaper. The cutting head is geared up and spins at 10,000 RPM's. It takes several seconds to reach operating speed and only runs on it's own dedicated 20 amp circuit, otherwise it pops the breaker.
I once had a need to use my large compressor out in the field. My generator would not start it with pressure in the tank. It would start when there was no back pressure from the air tank. I plumbed in a relief valve between the compressor output manifold and the inlet system to the tank. Open the valve, start the motor. Compressor air is released to the atmosphere. Close the valve and it got to work compressing air. As long as I stayed ahead of the compressor everything was fine. If the air tank filled and the compressor shut off I'd have to be sure to stop and go through the drill again before the compressor tried to restart on its own as the generator really did not like the demands made on it.
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Gary O
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# Posted: 22 Mar 2011 08:15pm
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Wish we had a photo of MtnDon so we'd know what god looked like
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MtnDon
Member
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# Posted: 22 Mar 2011 09:35pm
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This help?
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Gary O
Member
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# Posted: 22 Mar 2011 09:54pm - Edited by: Gary O
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some
but I'm not huntin' ya, so a profile ain't doin' it
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2Dogs
Member
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# Posted: 22 Mar 2011 09:58pm
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Another question might be since the Honda3000 started the saw would other cheaper gennys with 3000 surge watts do the same or is the Honda so well built it was able to start the saw and where lesser units would not?
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MtnDon
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# Posted: 22 Mar 2011 10:13pm
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go find it.....
http://www.small-cabin.com/forum/8_941_0.html#msg10155
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hebegbz
Member
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# Posted: 22 Mar 2011 11:01pm
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Table saws, drill presses, and anything with a compressor will pull a big load when you start it.
I have a Honda 3000w genset and it won't run my 120v air conditioner, the drill press or the shopsmith. The 20 amp outlet trips before the tool gets up to speed. It's not so much that the genset doesn't have enough power, more that the breaker trips.
Many motors that run on 10 amps pull much more as they start.
If this isn't for your everyday power you can use one of the 5k units they have at Costco. They will easily run all your tools and have the outlets to do it right. Also, keep your extension cords as short as possible to minimize your voltage drop.
Also, you can use the 10hp china diesel units, they have the power, the outlets, and the advantage of diesel fuel.
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MtnDon
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# Posted: 23 Mar 2011 10:14am
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Quoting: hebegbz It's not so much that the genset doesn't have enough power, more that the breaker trips.
Unless the breaker is defective, trips at too low a load, it is telling you that the generator may be damaged if more current is pulled. The tripping breaker is doing it's job as the manufacturer feels more than that will overload the generator.
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toyota_mdt_tech
Member
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# Posted: 7 May 2011 06:36pm - Edited by: toyota_mdt_tech
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Quoting: 2Dogs Help. I'm having trouble sizing a genny. I need the smallest genny that will power my biggest tool. The genny will be used to run my power tools and top off my batteries if needed. I have written the tool manufacturer but cannot get an answer from them. What I need are the starting amps. The tool is a DeWalt 746 table saw. It is 1 3/4 hp 15 amp 120v. It has an induction motor. Code G Every table I have read on motor starting amps says a 1 1/2 hp motor should be 4200 to 4900 watts to start. I would rather have a smaller genny than that if possible. I borrowed a friends Honda 3000 Handi inverter generator and it started and ran the saw just fine but I don't want to spend$2500 on a genny. $1000 is about tops. The mortor manufacturer ( Marathon) is no help either they say talk to DeWalt.
Honda EU2000i, Wise sales has them for $850 shipped. I have ran all my power tools with this generator, even my air compressor for air nailers. My biggest start up load is a worm drive skil saw. Consumes more than a regular one.
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Brenn
Member
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# Posted: 17 Oct 2011 05:08am
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I also need power tools for home renovation and I think I will use a power rental service. I am also not quite sure about the sizing of the generator. Hopefully the provider can tell me exactly which generator size I will need. Besides this I will definitely need some other tools. Hopefully I will get everything I need for my home renovation.
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bobbotron
Member
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# Posted: 6 Sep 2012 09:38am
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I know this is an old thread, but here are my 2 cents. Go for a 5000 watt generator if you're going to run power tools. I bought a 3500/4000 watt champion generator which croaked during my build. It would run everything except 15A tools. We then rented a 5500 watt generator, which was loads better in every way than my champion (except for weight, it was quite heavy.)
For running medium to big 120V power tools, give the 3500W/4000W range generators a pass!
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