Evaluating the DIY 120v compressors on output vs. specs

pipsters · Feb 20, 2012

Evaluating the 120v DIY compressors on output vs. specs

I'm trying to compile a real world fact sheet of 120v compressor performance because we know that the ratings they put on them are bunk. So, using a formula I found online, I am able to calculate the average CFM flow over the course of filling the compressor.

Current rankings from best to worst, ~150 psi compressors:

Craftsman 25 gal 150 psi 8.5 CFM average (75 psi avg)
Kobalt 30 gal 155 psi 6.0 CFM average (77 psi avg)
Harbor Freight 29 gal 150 psi 5.9 CFM average (75 psi avg)

Current rankings from best to worst, ~135 psi compressors:

Husky 30 gal 135 psi 6.9 CFM average (68 psi)
IR Garage Mate 20 gal 135 psi 6.0 CFM average (68 pis)

Ranked by PSI rating, because the higher the PSI the much longer it takes to get to that level.

Below are reviews on the individual compressors:

Harbor Freight 29 gal 150 psi 120v $349

This guy filed his new 29 gal 150 psi 120v compressor from HF from 0 to 150 psi:

6:40 secs to fill the tank. Using the formula I calculated roughly 5.9 CFM, which is exactly what they quote. Only question is, at what PSI? They state 90 psi however that is taking the average from 0 to 150. I do not know the relationship exactly but generally the lower the PSI the more air the compressor will move, so that would be over an average PSI of 75 (0 to 150 divided by two). Not sure if you can do that or not but anyway it is what it is.

Craftsman 25 gal 150 psi 120v $499

Craftsman Pro 25 gal 150 psi 120v, using the same formula, goes 0 to 150 psi in 4:01. Equates to roughly 8.5 CFM, however again that would most likely be around @ 75 PSI taking the average.

So, while the Harbor Freight unit lives up mostly to its' specs, the Craftsman unit blows theirs away.

Kobalt 30 gal 155 psi 120v $413*

*10% movers coupon, reg. $459

Lowe's Kobalt brand 30 gallon 155 psi compressor (note: this review was for the older one that had a v-cylinder config) 7 minutes 8 secs according to a review @ Lowes.com. Using the calculation above this results in an average CFM of 5.92. Very similar to the Harbor Freight model.

Ric in Richmond (below) posted 7 mins flat, that equates to about 6.0 average CFM.

Husky 30 gal 135 psi 120v $360*

*10% Movers coupon, reg. $399

From Terra Nova below, Husky's 30 gallon 135 psi compressor will go from 0 to 135 psi in 5:20. Looking like an average CFM of 6.9.

IR Garage Mate 20 gallon 135 psi 120v $539

According to user 6-speed, his new IR 20 gallon 135 psi unit pumps up from zero to full pressure in 3:56. That equates to right at 6.0 CFM average.

Please post if you have any info! I just need time to go from 0 to whatever PSI your compressor tops out at.

pipsters · Feb 20, 2012

A bump, looking for time to pressurize the Kobalt 30 gallon 155 psi unit and Husky 30 gallon 35 psi unit....I know people have them, some people bought two when Lowes was getting rid of them...

pipsters · Mar 1, 2012

Updated the Lowes/Kobalt 30 gallon compressor info

Ric in Richmond · Mar 1, 2012

I timed my cobalt with the older 2 cylinder.

7 mins flat about 40 degrees ambient.

Wonder what the "new and improved" one does?

pipsters · Mar 2, 2012

Ric in Richmond said:
I timed my cobalt with the older 2 cylinder.

7 mins flat about 40 degrees ambient.

Wonder what the "new and improved" one does?

Thanks added under the appropriate header, hopefully more people will post up about their compressor.

pipsters · Mar 11, 2012

Added the IR Garagemate info. Most of them are right in line. I am surprised at the Craftsman's performance, maybe the tank is smaller than published?

Terra Nova · Mar 11, 2012

Just timed my Husky 30 gallon. Ambient conditions = 62 degrees and 27% humidity

5:20 to 135 psi.

Breakdown as follows:
1 min to 50
2 min to 75
3 min to 100
4 min to 120

The last 15 psi took a while...

ecidious · Mar 11, 2012

The ridgid tri-stack 5 gallon compressor I have for my nailers filled up from 0 to 150psi in 79.5 seconds, equating to an average of 5.1cfm so I'd say it's rating of 4.9cfm at 90 psi is about right. Can't wait to get more than one 15 amp circuit to the garage for a 20+ gallon compressor.

pipsters · Mar 11, 2012

Thanks guys added the Husky 30 gal compressor as well. Worked out to 6.9 CFM average.

bsaint · Mar 11, 2012

Husky 30 gal 135 psi 6.9 CFM average
Kobalt 30 gal 155 psi 6.0 CFM average

Judging by the the change in CFM and pressures, these look like the same exact unit.

The problem is your CFM ratio math doesn't work because the CFM drop vs pressure increase is exponential and different depending on design. Its like the stress from 6000 rpm to 7000 rpm on an engine is far greater than going from 2000 to 3000 (as noted by Chief engineer of the Honda S2000 engine.)

You can change the CFM output by simply adding a finned discharge tube.

pipsters · Mar 12, 2012

bsaint I agree. But the Craftsman @ 150 psi still looks to be a clear winner, unless it's aluminum pump is heating up the air that much more that it makes it seem like it's pressurizing more than the iron pump compressors (on my Craftsman, when it hits 150 psi or so, it bleeds down quickly to 145 and then finally settles somewhere around 140 about 30 mins later). When I originally posted, the compressors were all in the 150 psi range.

Although the research I've done actually points to aluminum being the superior material as it will dissipate the heat much better than an iron head would.

Also looks like the Garagemate is a clear loser as well.

Not sure I understand about the finned discharge tube though. Are you saying a finned tube to cool the air going into the tank? If so that would make sense, although I don't think any of the current compressors offer that feature.

It would be better to get time to charge from say 80 to 110 psi, although I felt that would be too complicated to get results back.

So I guess moral of the story is the stats the companies are putting on their compressors seem to be pretty accurate these days?

bsaint · Mar 12, 2012

Yes I think the Craftsman one is a winner too!

My HF had a finned discharge tube, a feature I was surprised to find as seeing only higher end pumps have this and when rebuilding it should be noted not to replace a damaged one with straight copper tubing.

Aluminum does make the best cylinders, and if you look into it, Champion R pumps (not the Advantage series) have aluminum heads with steel sleeves.

theoldwizard1 · Mar 12, 2012

While those may be rated as 120V, I will bet none will work on a 15A circuit !

pipsters · Mar 12, 2012

My Craftsman will work on a 15 amp line provided its not right next to the panel.

weesss · May 31, 2012

Hello, just found this board. I am interested in buying this Harbor Freight 29 gal 2 stage compressor and want to get an idea of how loud it is. i have a single stage, which is quite loud and want something with a little less sound and more power if possible.

Bo Heck · May 31, 2012

theoldwizard1 said:
While those may be rated as 120V, I will bet none will work on a 15A circuit !

I have the IR garagemate, it will run on the 15A circuit. I can't run it and the shopvac at the same time though.

GirchyGirchy · Jun 4, 2012

Shucks, wish I'd seen this before buying mine. That Husky seems like a deal. I'll measure mine tonight though.

pipsters · Jun 4, 2012

GirchyGirchy said:
Shucks, wish I'd seen this before buying mine. That Husky seems like a deal. I'll measure mine tonight though.

Not really the Kobalt and Husky are the same and/or VERY similar, the Husky has less PSI and it's the top end that takes forever to pressurize.

The clear loser is the IR Garagemate, 135 psi @ 4 mins on a 20 gal tank. The Craftsman does 150 psi on a 25 gallon tank in about the same amount of time.

z28snksknr · Jun 4, 2012

For consideration, my 3 year old Kobalt times in at ~8min these days, depending on temp and humidity.

Now that I have 220V in the garage and my tool useage is exceeding its limits, I'll be upgrading to a 60gal unit in the near future.

GirchyGirchy · Jun 4, 2012

pipsters said:
Not really the Kobalt and Husky are the same and/or VERY similar, the Husky has less PSI and it's the top end that takes forever to pressurize.

Yeah, but the Husky is $60 cheaper and much better reviewed. For some reason check the reviews at Lowe's for the Kobalt....pretty bad.

Major Ramifications · Jun 27, 2012

Re: Evaluating the 120v DIY compressors on output vs. specs

pipsters said:
I'm trying to compile a real world fact sheet of 120v compressor performance because we know that the ratings they put on them are bunk.

What did I miss? So you are saying that the SCFM @ 90 PSI ratings that are on the compressor are not accurate? What are you basing this on?

pipsters · Jun 27, 2012

Re: Evaluating the 120v DIY compressors on output vs. specs

Major Ramifications said:
What did I miss? So you are saying that the SCFM @ 90 PSI ratings that are on the compressor are not accurate? What are you basing this on?

A 6hp 120v compressor? Do you believe that?

In the past I have questioned CFM ratings especially those from Harbor Freight.

pcmeiners · Jun 27, 2012

6 hp either derived by calculating input wattage, as motor goes up in flames, after incorrectly connecting it to 220v line or is it derived by the total horse power the full tank of air will produce

Get a kick out the definition of SCFM

http://en.wikipedia.org/wiki/Standard_cubic_feet_per_minute

.."but not always"

Then you read this, and you have redefine what standard means. It appears to mean whatever is easiest/convenent/benefical to you or your organization at the moment ...

http://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure

"...The table below lists a few of them, but there are more."

Major Ramifications · Jun 27, 2012

We all know that the HP ratings are useless, but we have been preaching the SCFM @ 90 PSI figure as an apples to apples comparison point for years.

6-Speed · Jun 27, 2012

For these smaller compressors it might be good to list how many are rated for 100% continuous duty. I know the IR Garage Mate is, but how about the others?

pipsters · Jun 27, 2012

6-Speed said:
For these smaller compressors it might be good to list how many are rated for 100% continuous duty. I know the IR Garage Mate is, but how about the others?

That is a good point. The Craftsman does say continuous duty is approved although to prolong the life of the compressor limit it to 30-45 mins of run time per hour. Probably goes for everything!! Haha.

Evaluating the DIY 120v compressors on output vs. specs

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