Gas generator for air compressor


  #1  
Old 03-11-06, 02:14 PM
L
Member
Thread Starter
Join Date: Mar 2006
Posts: 4
Received 0 Votes on 0 Posts
Gas generator for air compressor

Howdy. Hope somebody here can give me a clue. I'm running a Sears Pro model oil-free pump 25 gal compessor. It's pulling 15 amps with a max of 175 psi cut in at 140 psi. I'd like to buy a gas generator to run the compressor and a flourescent light (I'm a stone carver working out in a remote area). Just what kind of wattage in a generator will I need to get the job done? Thanks for any input. KW
 
  #2  
Old 03-11-06, 02:33 PM
S
Member
Join Date: Aug 2003
Location: Cape Cod
Posts: 4,320
Received 0 Votes on 0 Posts
Amps of what you want to run X volts = what you need

The compressor will need 15 x 120 (I'm assuming it's a 120 volt 'pressor) = 1800 watts

Keep in mind the things you want to run that draw regular-like radio, lights, and remember the compressor doesn't run continuous, but when it kicks on, it kicks on but good
You want enough wattage to run the lamps when the 'pressor kicks on

I've got some figures somewhere around here for florescent lights and such, but I'm sure 2000 watts will be fine for what you need
 
  #3  
Old 03-11-06, 02:42 PM
L
Member
Thread Starter
Join Date: Mar 2006
Posts: 4
Received 0 Votes on 0 Posts
Quick answer!

Thanks. I'm looking for low maintenence and a long life so thinking Honda.
Thanks again, KW
 
  #4  
Old 03-12-06, 05:03 AM
M
Member
Join Date: Jan 2005
Location: Texas
Posts: 478
Received 0 Votes on 0 Posts
I may be wrong, but I think you'll need more gen than that due to the fact starting amps for the compressor will be several times higher than the max running amps.
Mike
 
  #5  
Old 03-12-06, 08:07 AM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 10,198
Received 54 Votes on 50 Posts
lumpy,

My suggestion would be to size your generator to at least double the running wattage.
A compressor starts and stops quite often and would soon wear out too small a generator.

I own a 4500 watt Coleman for occasional use and find it to be a very handy size.
It can operate a small compressor and enough lights to illuminate a large area.
With this size it will power up quite a few household devices in an outage and even run my MM150 220 volt mig on lower settings.

There is no denying that honda makes a quality product but if you only have occasional use for a gen,for the money you may have better luck with a less expensive larger generator than an undersized Honda.

If I have a need for a lot of air I just use a gas air compressor.
Another option for you that may be more efficient is to purchase a gas powered generator with a Honda engine and a small suitcase style gen for the light.
 
  #6  
Old 03-12-06, 09:28 AM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 48,162
Received 408 Votes on 364 Posts
You definetly want to make sure you have a big enough generator - better for it to be oversized than undersized. I have a 5000 watt generator that is more than stout enough to run a .75 gpm airless but it struggles with my little 1 hp 11gal sears compressor.
 
  #7  
Old 03-12-06, 03:03 PM
M
Member
Join Date: Jan 2005
Location: Texas
Posts: 478
Received 0 Votes on 0 Posts
My suggestion would be to take the compressor with you to make sure the gen you want will start it @ 140 psi.
Mike
 
  #8  
Old 03-12-06, 07:06 PM
IBM5081's Avatar
Member
Join Date: Oct 2004
Location: Texas
Posts: 655
Received 0 Votes on 0 Posts
I have a 2200 watt Honda and a 2 h.p. 4-gallon air compressor. When the compressor is empty (no back-pressure), the generator WILL start the compressor. It will run it until the limit switch shuts it off. It WILL NOT restart the compressor once it has pressure in the tank.
It works fine on my 8 kw generator. I would think 3500 - 5000 watts would be required to start that compressor once it's loaded.
 
  #9  
Old 03-13-06, 12:40 PM
Pendragon's Avatar
Member
Join Date: Jul 2002
Location: USA
Posts: 1,851
Received 2 Votes on 2 Posts
First, 1800 watts will NOT be enough to start your compressor.
You need to be looking into something that has a 6kw 'surge'. This will probably put you into the 3-4kw size area.

A larger generator doesn't always use more fuel than a smaller one since fuel consumption is part engine size/rpm and part load. A smaller generator running at full load will use more fuel, work harder, run hotter and last less time than a larger generator running at partial load.

And you will always find something else that just has to plugged in.

IBM: You can install an unloader valve that will release pressure from the compressor for startup. Most of the larger compressors have these already, and I am betting his 175psi one does.
 
  #10  
Old 03-16-06, 09:03 AM
L
Member
Thread Starter
Join Date: Mar 2006
Posts: 4
Received 0 Votes on 0 Posts
Unloader valve?

Never heard of one. Can someone tell me what it is and its function? Thanks
 
  #11  
Old 03-16-06, 09:18 AM
IBM5081's Avatar
Member
Join Date: Oct 2004
Location: Texas
Posts: 655
Received 0 Votes on 0 Posts
Both of my portables have the unloader feature - air vents to atmosphere (rather than into the tank) for the first 5-15 seconds when first started. Both are oil-lubricated. I do not notice the unloading feature kicking in once there is some air in the tank, as would be the case when the pressure falls to the lower limit pressure.
 
  #12  
Old 03-16-06, 09:22 AM
Pendragon's Avatar
Member
Join Date: Jul 2002
Location: USA
Posts: 1,851
Received 2 Votes on 2 Posts
An unloader valve does just what it sounds like. It 'unloads' the air pressure between the compressor and the tank, so that when the compressor starts, there is no pressure for it to start against.

Here's a link that describes one type..
http://www.generalairproducts.com/PD...20Page%204.pdf
 
  #13  
Old 03-16-06, 09:26 AM
Pendragon's Avatar
Member
Join Date: Jul 2002
Location: USA
Posts: 1,851
Received 2 Votes on 2 Posts
If your generator will start the compressor when pressure is low, but not when it's high, then I'd say you do NOT have an unloader valve (or the one you have isn't working). There is no load on the motor when it starts, regardless of air pressure in the tank, that's kinda the point.
 
  #14  
Old 04-14-06, 09:31 AM
L
Member
Thread Starter
Join Date: Mar 2006
Posts: 4
Received 0 Votes on 0 Posts
The solution

I wanted to thank everyone who helped with my questions here. The issue which spawned my initial
query was that the only power source at my worksite (I'm a stonecarver) was 250' away. So, someone smarter than me suggested I put my compressor at the power source and run the distance w/ airhose. Viola! Someone has since suggested putting a second 20 gal. storage tank down where I'm working. Will (probably a dumb question) this lessen the workload on my 25 gal. 3.5 hp compressor? Good or bad idea?
Thanks, KW
 
  #15  
Old 04-14-06, 10:25 AM
J
Member
Join Date: Sep 2005
Posts: 70
Received 0 Votes on 0 Posts
Originally Posted by lumpykevlar
I wanted to thank everyone who helped with my questions here. The issue which spawned my initial
query was that the only power source at my worksite (I'm a stonecarver) was 250' away. So, someone smarter than me suggested I put my compressor at the power source and run the distance w/ airhose. Viola! Someone has since suggested putting a second 20 gal. storage tank down where I'm working. Will (probably a dumb question) this lessen the workload on my 25 gal. 3.5 hp compressor? Good or bad idea?
Thanks, KW
I'm no pro, but I think adding another tank (which you have actually already done by using such a long length of airhose) would actually increase the load on your compressor. i.e. more volume of air to keep under pressure.
 
  #16  
Old 04-14-06, 03:59 PM
M
Member
Join Date: Jan 2005
Location: Texas
Posts: 478
Received 0 Votes on 0 Posts
If you go the 250' hose and 20gal tank route, spend some extra and use 1/2" hose for the 250'. Otherwise the 20 gal tank won't help much due to frictional loss in a smaller 250' hose. I'm not sure if 1/2" will be large enough for a run that long. It all depends on how many CFM your air tool(s) use.
Mike
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: