Jobsite Generator Sizing

personalt

Most jobs I do have at least temp electric power so I dont have a jobsite generator. I have a job coming up where the power is underground and we cant get temp power until at least the block is up.

Mostly I am looking to run equipment for 3-4 guys for block and framing. I could get a gas cement mixer and a gas compressor but since I need electric for circular saws I figure I should get an electric generator to run the electric tools I have now.

I am looking to power(not necessarly at the same time)

-a compressor for air nailers. medium double hotdog style
-circular saw

-a small cement mixer for morter for block. Any big amounts of concrete we get delivered

-in a pinch my electric jack hammer

Any advice on size?

G-Build

Assuming your hammer is 15amps you'll need a generator rated at 2000 watts continuous, 2500 surge or starting watts. I'd call that the minimum.
If you plug something else in it may be no go. I'd go with a 3500watt jobsite gen. Gens arent cheap if you buy the minimum now and need more later.....
You get what you pay for. I bought a B&S $750 5500watt gen, it's so loud i stopped using it. It's collecting dust in my garage.

1018

I've heard its incredibly bad to run compressors off of generators, I think theres a possibility of it not keeping up with the output and surging - which would leave you with no compressor. Look into getting maybe a small gas one, are you going to run framers or just some finish guns?

Another option would be getting a gas compressor-generator combo, a little more costly but depending on the size of the job it might be worth the investment.

Blackhammer

[quote=1018;419347]I've heard its incredibly bad to run compressors off of generators, I think theres a possibility of it not keeping up with the output and surging - which would leave you with no compressor. quote]

The problem occurs when people use an extension cord for the compressor and less air hose. That is a problem on any type of power. I have a 8k running and 13500 surge generator we use every day. I have run the compressor off it several times for long periods of time with no problems. We did a roof on a house using the generator and compressor for 5 days and no problems. The killer is the extension cords.

1018

Yeah, I've always been taught to run more air hoses than extension cords. And with the size of your generator I'm sure its not an issue, but with a smaller one I'm sure there would be some kind of injury to the compressor.

IF you haven't already bought one, the big box is having a 10% off on all (most?) generators plus free shipping. Not sure if it's online only, but its worth a look.

homedepot.com/webapp/wcs/stores/servlet/Navigation?N=524798+6+90401&langId=-1&storeId=10051&catalogId=10053

DrewD

It is harder on power tools to run off a generator, it not a constant feed like from a pole. Look at getting a good quality, I know that Yamaha brands have a built in protection device that prevents damage to sensitive equipment. I really hate running my tools off a generator for a long time.

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Magnettica

There is no difference what you plug your electric tools in to. Wether it be a gas-powered generator or utility power from the electric company. Both means transfer energy from one form to another. One uses gasoline, one uses coal, some use water to turn turbines that generate a voltage. Nonetheless, all of them are separately derived systems and will operate your power tools the same way.

5,000 watts for the genny is good for up to 20 amps. 5k/ 240 = 20 and change. That should be alright for most compressors and cordless battery chargers. Obviously, unplug the compressor before using something else of significant power or you could damage the copper windings within the generator itself but the built-in fuse should trip before that happens.

Good luck.

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mickeyco

Question, are the smaller cheaper generator true sine wave or modified? I'm thinking modified on the cheap ones and true for the expensive ones, I see 2000 watts for about $200- $500 and then 2000 watt units like the Honda or Yamaha that start at $1000. Not a problem for most applications but modified sine's are not good for microwaves and sensitive electronics. Anyone know, just curious.



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MasterEngineer

I would go with any of the big Honda generators or the Miller Electric. Also, make sure the generators are GFCI protected. Sometimes in contruction, you have to work in the rain........ , plus GFCI is an OHSHA requirement.