Air compressor upgrade

[mustangmatt70]

I have a harbor freight special 21gal 2.5 horse air compressor. It doesn't keep up with me when I grind, cut, or sand something. I found a craftsman 60gal 7 horse air compressor on craigslist for $300, I was wondering if this would be ideal for automotive restoration and repair?

Thanks,
Matt

 

[sberry]

Maybe, might be able to get one similar for about 5 new.

 

[sberry]

Sometimes its worth looking, never know for sure exactly what it is.

 

[StevenMorgan]

Check the motor dataplate. Verify that it isn't those "advertised" 7HP models that actually can't put out 3hp! A no kidding 7hp compressor is awesome and would easily keep up with everything short of sandblasting.

Someone will be along who knows those amp output/per HP at 220v, but its not me.

 

[joe_padavano]

Check the motor dataplate. Verify that it isn't those "advertised" 7HP models that actually can't put out 3hp!

^^^^THIS! Most "homeowner" compressors are rated at "starting horsepower" or some similar term that is just marketing BS. It refers to the instantaneous HP the motor generates in the first quarter turn or so and while not lying, it's about as close to deceptive advertising you can get and stay out of jail.

Look at the motor voltage and amps. I'll assume this is a 220V motor, as no 115V motor will come close to that kind of HP. A real 6-7HP 220V motor will pull 25-30 amps. If the motor is rated at less than that, it is far less than an 7HP motor.

 

[engineer2]

I always look a the cfm @ 90 psi spec. I Craftsman that died was 11.5 cfm @90 psi and it could keep up with about everything in in the garage, including the sandblaster.
Today I'm looking at a new Sanborn that is rated about the same.

 

[redmondjp]

I always look a the cfm @ 90 psi spec. I Craftsman that died was 11.5 cfm @90 psi and it could keep up with about everything in in the garage, including the sandblaster.
Today I'm looking at a new Sanborn that is rated about the same.

Sorry, but that doesn't tell you much either unless it is an industrial compressor (on which the advertised numbers are pretty accurate). They lie about CFM ratings on the consumer-grade units as well, as they use the short-term boost from the tank volume to goose the numbers.

My 25-year-old Rand-4000 has a similar CFM rating as yours, and it can't even keep up with air tools that claim they only need 4cfm. No doubt the tool number is bogus too, and may take twice what is claimed on the box.

I'm getting ready to set up my Quincy 325. It came with a 3-phase motor and I recently bought a Marathon 7.5HP single-phase motor for it (only need 5HP but got a great deal on it). This compressor will outlive me for sure!

 

[sberry]

Your tool takes 12 cfm , not 4.

 

[engineer2]

They lie about CFM ratings on the consumer-grade units

Those bastards! What you say makes sense. I'll find out when I finish hooking up may Sanborn tonite.

 

[PT Doc]

80g, 2 stage, 5 hp should sort you out.

 

[Finky198]

There is what know as. Average CFM rating and @ Load CFM ratings

Let's say for instance my 2135TiMax there's the average CFM consumption is 5 to 6 CFM for taking off a lug nut or reg fastener in a 2-5 second trigger pull. But At full load this tool requires over 20 cfm In other words if the tool is being used constantly at load it's going to require four times (In this instance ) the amount of air as short bursts to remove a low torque fastener say lug nut. versus let's say A honda crank bolt.

Don't even get me started on our 4.5 air grinders or large air hammer

Your air compressor is probably one of the most valuable tools in your shop if you're going to seriously get into the market of air tool by the biggest damn compressor you can afford


We currently are using a 7.5hp 80 gal ingersol rand rated at 24 cfm and sometimes I still need more air