Generators for running power tools

[cedarglen]

I will be building John's 2 story universal one day a week for the next few years. I have a compressor which says it draws 15 amps. My saw is less than that and I won't run both at the same time. It looks as if the 3500 watt generators on eBay put out 15+ amps and sell for about $300 shipped. That is close to 1/2 of the price I can buy a 3500 watt generator for at Home Depot or Costco here in CA. Are these no name generators on eBay going to do the job for me? Am I right that a 3500 watt will do the job? Anything I should know before I buy?

Thank you
Chuck

[MountainDon]

Compressors are one of the hardest things to run off a generator in my experience. They usually have a significant start up load. Another factor to consider the altitude where you plan to use it. Rough rule of thumb is 3% power loss per 1000 feet of elevation.

I had a 4000 watt gen a number of years ago that would not start my compressor, an average 20 gallon home shop type. Mind you I'm at 5500 feet average around here, so that would have been less than 3400 watts available. I made a temporary work around, but it was too much trouble. Things were much better when I got a 6500 watt generator. All those low priced generators are also noisy as he**.

[glenn kangiser]

A noname from Ebay sounds a bit scary to me.  The problems of trying to return it make the price a bit less important.  Something like that I like to deal with someplace I can take it back to if problems develop.  

I have a 3000 watt generator on a Lincoln Weldanpower that will start a large carry around compressor 6.2 cfm @ 90 psi Campbell Hausfield 15 A- but it is a higher quality fairly expensive 9 HP generator -welder combined.  It will  also start it loaded when the compressor kicks in.

[builderboy]

I was thinking about building with generator also. I will have on grid power but it looks like I can buy a generator for about the cost of installing and removing temporary service so I might as well end up owning a generator. Is there any way of knowing whether a certain generator will do the job ie will it start my compressor (as mentioned by mountaindon). What matters here? horsepower? Wattage? Elevation isn't an issue at about 100 ft.

[builderboy]

Oops. Make that 100 meters = 328 ft.

[glenn kangiser]

It would be more it's surge capacity and the starting requirements of the compressor motor especially under load which can be around 10 times the rated power depending on the motor.  The motor I have says 14.5 amps but empty the compressor only draws 8 amps -- I didn't watch it loaded or starting.  Some generators may not take the startup surge so in that case bigger is better.  15 amps at 120v is only 1800 watts but startup can be much higher.  Generators don't really have a rating to tell you about surge capacity although some may have a temporary load rating that is higher.  Best if you can try it.

Watts = Volts X Amps if you want to estimate safety factors.

[JRR]

I also have a Lincoln welder/generator.  I think mine is rated at 3500 watts, and like Glenn's, it has supplied some impressive start-up loads.

But I wonder if welder/generator's might be better at this, compared to straight generators of same wattage, because the additional welding windings offer extra weight on the shaft that supplies rotational inertia ... helping to overcome start-ups.

Just wondering.

[MountainDon]

I think those Lincolns are probably built better, with a more conservative rating than many of the low dollar generators.. It may be just me, but that's my opinion for what it's worth.

Just like some of the low cost inverters. I've seen some sold as, say 1000 watts, but the fine print states "but only up to 30 minutes of use".

And many places won't take a genset back if you've put gasoline in the tank. A question to ask oneself before buying something like this is, might it be used further down the road for emergency power? Or whatever. Buying more or better than you think you need could pay off in the future. And it'll cost more now.    If you go that route keep in mind the safe storage of fuel, re-newing the supply once in a while,  the bother to run it every so often, etc.

One last thing; I have a friend who has a genset from Northern Tool. Honda iron sleeve engine that runs on gasoline, propane or natural gas, at the flick of a switch. Something like 6000 watts, 8000 surge and $2000 or so. Running on "dry" fuel it gets de-rated some but it's kinda nice to have it sitting there hooked to a 100# propane tank, knowing its ready and waiting.

[glenn kangiser]

I think the Lincolns may have some extra kick in there for starting.  I have built a rotary phase converter before where you run a three phase motor on single phase with heavy capacitors on the third leg to induce a current into it and run and start a 3 phase motor of equal or smaller size.

The third leg power is generated off of the single phase power so all three legs generate.  That really makes sense doesn't it? :-?

The capacitors offset the timing of the third leg so it will push at the right time.  

Lindsay Publications publishes a booklet that tells how to do it.

[MountainDon]

That really makes sense doesn't it? :-?

Most people's eyes glaze over when you get into single phase, 3 phase electricity.  And most people don't realize that computer fans are often of the 3 phase flavor to help make them extra quiet. They use an inverter circuit to change the DC into 3 phase AC. (Today's Trivia fact)

And speaking of big capacitors...  :-? Some RV air conditioners won't start when running off a genset at higher altitudes. Adding  some big capacitors frequently provides that extra ooomph to get them going. Available as a "soft start" kit for many. I wonder if something like that could assist a compressor start?  

[glenn kangiser]

Interesting -- I had an inverter going out in an older laptop flat screen but I just try to replace my laptop evey few years instead of fixing the small stuff.  I got the part but didn't install it.  I think Windows Vista stopped me from upgrading for a while -- I don't want any more federal government in my computer than I already have.  NSA assisted Microsoft in testing out - therefore setting up Vista and maybe the plumbing for the back door.  Doesn't matter much though - they can get into the rest of them too.

I'm not sure about extra capacitors - they might help - most compressors have a couple pretty big ones already.  Guess I'd want to know more -- I made big sparks building my rotary converter.

[cedarglen]

I've found a 5250 (6500 surge) watt generator in my price range. It is made by Porter Cable for and branded PowerBack. My research leads me to believe that there is a pretty good chance that this will handle my 15 amp compressor at 5500 feet elavation. What do you guys think? What do you think of PC products?

Chuck

[glenn-k]

I think it would probably do the job.  I have a PC FR350 and the Tiger Claw articulating Sawzall type saw.  The framing nailer is good an there is no comparison for the saw.  It's great.

[Amanda_931]

If you

a) really really hated noise (my smallish Porter Cable generator that the dogs eventually buried was awful)

and

b) weren't sure about ever getting grid power

you might look into starting off-grid--putting wind or PV or (lucky you if you can do it) micro hydro in to start with, then go eventually with a small generator for when you have problems with the rest of the system--two weeks in January without seeing the sun, for instance.

I have heard that most people have enough power to build their house if they have enough power to live in it.

[hobbiest]

Spring for a gas powered compressor, or you will risk burning up your compressor motor, or throwing the breaker on the generator every time the compressor refills.  Build a wall between the generator and compressor, and your building site, and spring for more and better hoses and cords to get to the tools.