Replies

1. 
   DScott_ | Jul 09, 1999 02:46am | #1

   *
   I'm unclear about the quality of power output from a generator, but assuming it is as rated two things come to mind: 1) if you start to add load engine RPM's are likely to decline and power output may decline, so be careful about running too many things at once or driving the tool hard and fast; choose a gen set with ample driving engine power as well as rated output (more HP is better, more expensive gen sets produce rated output at lower engine RPMs which is better still for long run times). 2) I'd run any high amperage draw tool on a 10ga cord, particularly over 25 ft., absolutely over 50 ft.
   (100 ft. 10/3 cord was about $75 when I bought it at Home Depot, but I don't see them stocking them any more.)

   It's voltage drop -- running a tool under load at less than specified voltage -- that shortens motor life.

1. 
   mark_cadioli | Jul 10, 1999 06:13am | #2

   *We have found that a 5kva will just pull a compressor, however if we wanted to use say a mitre saw at the same time the gen didn't like it and neither did the compressor.

1. 
   Dave_Wright | Jul 10, 1999 07:59am | #3

   *I have a cheap Coleman Powermate 4000 watt generator. It produces 125 volts at the machine, so there is still good voltage at the other end of my 12 gauge cords. It seems to hold 60hz pretty well, though there is a throttle lag when the load is applied. Tools run fine off the generator, including 15 amp saws.The power curves must be slightly odd because some non-tools, like a microwave oven, run strangely. This may be a factor with more sophisticated electronics than typical power tools.The generator is darn loud, though. I installed Coleman's separate $85 "better" muffler, which only helps a little. It would be worth the money to get a quieter generator instead.

1. 
   DScott_ | Jul 10, 1999 05:55pm | #4

   *Hi Dave. You raise an interesting question about noise. Way back in my youth i seem to remember Popular Mechanics or some such magazine showing a farm generator with a large automotive type muffler installed.Anybody know what the deal is on this? Can you put a really large muffler on a small engine to cut noise levels without degrading engine performance? I guess you'd have to rig up some bracing so it didn't snap off if hit and it would make for a bigger package to haul around. My principal interest is for an emergency power source for my mother's house.Are the little Honda generators so quiet because of muffler design or engine design?

1. 
   lonecat | Jul 10, 1999 09:11pm | #5

   *I knew I could count on you all for thoughtful replies. Over on jlconline I just read a brief discussion on shopping for a new compressor, and one guy mentioned that he had a little one which was easily converted to 220 volts so that he could run it off his 5000watt generator. I've got a good compressor at home, I'm just wanting to run a portable that's just big enough to run a shingle nailer, and I am a slow roofer. Is 2 or 3 cfm plenty for one roof nailer? Seems like it should be. And what about this 220 aspect? Thanks.

2. 
   Gregoryj | Jul 10, 1999 09:34pm | #6

   *Hi, I'm the one who posted on JCL about running my compressor at 220v off of a 5kw generator. The 120v compressors I tried to run would start initially but not when pumped up. Even with those that bleed pressure off the head for easy starting there just wasn't quite enough to get it going. At 220 I can run other tools while the compressor is running.As far as the noise goes it is the engine design that makes most of the noise. Honda and others that are quiet use overhead valve engines and that is why they are quiet. Very nice if you want to spend the money. For residential use it would definitely be worth the extra.2-3 cfm is plenty for one slow roofer.Put your compressor close to the generator run air lines insted of electrical cords.

3. 
   Dave_Wright | Jul 10, 1999 10:43pm | #7

   *Gregory's 220v solution sounds like it was specific to his situation. Probably there was too much voltage drop at 110. I would try running everything at 110 first since 220 is more dangerous from a standpoint of arcing and 2 hot wires.

4. 
   Dave_Wright | Jul 10, 1999 10:58pm | #8

   *I think both affect noise. I don't see how OHV engines would make less noise from a basic design aspect, but the Hondas seem to be better shrouded and damped. Water cooled generators are a different matter - very quiet engines. Two-cylinder engines would also be fundamentally less noisy because of their smaller exhaust pulses. I would guess the bigger factor to be the muffler. A good one is fairly expensive. Rigging another muffler to the genset might work, but mufflers are best tuned to the specific engine. You might lose power and also not cut sound by much.I recommend finding a good supplier of several brands, particularly with a repair shop, and asking to hear some in action. You might find the cheap Coleman too loud, the Hondas too pricey, but a premium Coleman Vantage or Generac (don't remember their model name) might be just right.

5. 
   FredB | Jul 11, 1999 10:39pm | #9

   *For awhile I was routinely running tools from large saws down to corded drills off generators so let me pass on my experience. It may be worth what it is costing you but here 'tis:Make sure whatever you are running off the generator accepts non-sine wave power. Some things like microwaves, some rechargers, etc demand pure sine wave or they malfunction.Buy a DVM that has a Frequency function and set up your generator to produce the correct frequency while under load. Many generators change rpm and frequency while under load vs no-load.Get a generator large enough to maintain stable power under starting conditions. Depending on brand I find 4-5KW generators will power up through radial arm and table saws and small air compressors for a couple of nail guns. If you need to produce more air than that you are probably better off just getting a gas powered compressor.I sometimes use a filter, like for computers to eliminate the electronic "noise". Things seem to last longer with the filter but I don't have hard analysis to support that.These little generators depend a lot on free air flow and unimpeded exhaust for longevity and reliablity. So, I don't box them in too tight and I don't dink with the exhaust beyond what the engine manufacturer will approve. Almost every creative way I've seen to reduce noise also reduces life. The exception is to put a panel covered with fibreglass batting between you and the genset with the hard side to you and the fibreglass toward the generator. That helps some but they are noisy beasts.I've seen just about every type and size tool run off generators so size of tool doesn't appear to be a factor; sizing and maintenance of the generator does.

6. 
   daved_ | Jul 12, 1999 02:37am | #10

   *LonecatI work as a general contractor and as a framing subcontractor. When working as framers we are often asked to start framing off a generator. This is the first tip that the contractor doesn't have his act together. We can work for one day off a generator. Snapping lines and laying the sill can be done. After this I am wasting my time. A large compressor, four worm drives and a chop saw don't work well off the generator. Framing homes is loud enough without having to listen to a generator.If I am forced to work off a generator in the future it will a large trailer mounted generator and I will only do it if I have no other job to go to.

7. 
   DScott_ | Jul 13, 1999 05:14am | #11

   *Regardless of power source size of tool/current draw does matter depending on cord gauge and length. Small tool lets you get away with light gauge and long length. Big tool doesn't. Most power tools come with a chart of acceptable gauges and lengths for given amperages. Starting against a load like a bound up drill or a pressurized air tank increases normal draw.

8. 
   lonecat | Jul 13, 1999 11:54am | #12

   *DScott: How about voltage drop in house wiring? I've been seeing lots of new houses done with all 14/2, and there are some mighty long runs in there. I think people plug 100 foot 16 guage cords into circuits that are already 60 feet from the box.

9. 
   DScott_ | Jul 13, 1999 03:59pm | #13

   *10-4. In last week's heat wave I ran a new 15a 12g circuit for the 9,000 BTU A/C in my mother's house. A/C had been on a branch circuit that wandered through the house and lots of other devices. Even with everything else on that circuit turned off the A/C had a tough time. On the new circuit it ran smoothly and efficiently. I suspect the old run was longer and in 14g. Installation specs for the A/C by the way allowed 14g. Bigger wire is better.I guess that's why the 1999 NEC calls for dedicated 20Amp recepticle circuits for bathrooms, kitchen counters (2!), laundries, A/Cs, microwaves, refrigerators and maybe more I can't think of.I won't buy a cord smaller than 12g anymore, regardless of length. If I go beyond 50ft. I drag out the 100ft. 10g.

10. 
    SamD_ | Jul 14, 1999 08:38am | #14

    *May as well add my two cents worth... As everyone noted, start up on a compressor is the tough aspect of using a generator. While everyone noted this, I'm not sure anyone mentioned the current draw on start-up for electric motors (especially something like a compressor) is 2-3 running current. If you have access to a clamp on amp meter, hook that up and start up the compressor... It may prove to be a little shocking (no pun intended). When sizing generators (at least in theory) the generator should be able to cover the maximum start-up draw you may present it with. In theory. This of course is violated all the time and is evidenced by slow starting compressors, saws etc. Part of the problem is the way the generators are advertised in regard to KW rating: it is always the surge rating. People use this as an operating rating and it "just ain't so". Size the generator according to rated continuous output rather than surge output and save the surge output for that time someone has an extra saw hooked up that no one knew about..... As for extension cords, bigger is better although those double "o" welding cables probably aren't necessary. Purely resistance loads are much easier for a generator to deal with because they are constant without the spikes of motor start-up- which of course is the case on a construction site. As for quality, well, you get what you pay for.....S.

2. 
   lonecat | Mar 11, 2000 08:39am | #15

   *
   I used to use a generator a lot, but back then I didn't own the tools and probably paid no attention to how long they lasted. Since then I've heard of guys who hate to use a portable generator. With Y2K coming, there are generators everywhere I go- 5000watts isn't too expensive. Is it hard on tools if you if you are using something hungry like a hole hawg or a small 13 amp compressor?