I don't know how I get myself in these spots but I do. I got this wild idea to build me a shop compressor. I bought a 5hp Y block 2 cylinder unit at HF on sale for $99.00. They had a motor on sale for $99.00 also but were out of it. It is a 3 1/2 hp but rated at 5hp. When I drove around to the back of the store to pick up the compressor I had to wate for the people to get it ready. I was talking to one of the men about it and he said that the motor would not be big enough to run it. What size do I need to get to run it? ... .....RUSTY

 

Your compressor motor may be different than mine, but my HF Y-block compressor is running off a 4hp 220v motor. Sounds like you are in the ballpark.

Not everybody in that store knows everything about everything...but many think they do. Set up what you have and see. replacing the motor later (if you have to) is no biggy.

 

3 1/2 rated at 5 hp? is this a 220V motor? No 115V motor can produce even 3 1/2 hp continuously. Like stereo amps, motor power rating are often inflated with math tricks like using the starting current draw to calculate HP rating rather than continuous draw. A motor may draw a large current for an instant when starting but would burn up in a few moments if that draw was continuous. There are a lot of factors to consider when sizing a motor to a compressor. Is the compressor a single or dual stage, are you going to run it continuously or use a pressure switch to turn it on and off, if you are going to use a pressure switch, does the compressor have a head unloader valve to release pressure on the pistons when the compressor starts, How many rpms does the compressor need to turn to produce the volume of air desired, what is the rpm of the motor and what drive ratio will be needed to turn the compressor over at the desired rpm? What are you planning to do with the air you produce? This will help determine the pressure and volume you need. Unless you are only interested in blowing up tires and beach ***** I think you are going to find your home assembled compressor inadeqate to do much serious work and all said and done more costly than buying a complete unit. BTDT!

 

Rusty ?

is this your unit ???

http://www.harborfreight.com/cpi/cta...emnumber=93786

it's rated at 13.4 cuft at 90 psi. The rule of thumb I've always heard is 4 cuft for each h.p. so for 13.4 you need 3.35 hp. minimum. But as AX said...you ain't gonna get that h.p. from a 120 v motor for long... and it seems like that compressor turns pretty fast. 1200 rpm . My old quincy 310 turns at about 800 and gives me 20cuft at 150-175 psi. It maxes out at 500 psi... but I ain't gonna be around at that pressure !!!

You're definately gonna need a little more h.p. to get optimum results (i.e. air tools, paint gun.. forget sand blasting though other than small scale)

True 5 hp is gonna cost you 220 volt service. And don't just run it off the air switch relay contacts... it's needs a starter/contactor in the circuit to get long time reliable service... I know cause I fused the contacts in my air switch in about a year of intermittent service. Can you say " quick... go throw the breaker!!!!! "when you see your pressure gauge pegged at over 300 pounds !!!

I can post a pic or two to show you the wiring I did if you like... I know the motor and starter add more $$$ to the equation.... but for long term dependability...it will be worth it... look around for a 5hp used... craiglist, motor shops...heck even compressor service co's might have one they'll part with... as for H.F. in general... you're looking at lower efficiency motors ... look for industrial rated motors rated for 'compressor duty'..

later
john

 

Thanks john thats the unit I got the motor I'm talking about is on the same page as the unit. It is a 220 motor. A diagram of the wiring would be great. Can it be wired to a pressure on the tank if it is a 220 switch. The Motor at HF has a starter on it and one to run it. It does not have a valve to release the pressure on the head. Wish I could figure out how to post pics on here. ........RUSTY

 

This is the motor at HF.
http://www.harborfreight.com/cpi/cta...temnumber=7570
.RUSTY

 

Rusty,
Why not go with this: http://www.harborfreight.com/cpi/cta...emnumber=34884
It's all ready to go, has a warantee and Puma makes a quality unit. (I have one of their 12V portable piston compressors) The parts to build yours will cost more than this.

 

AX that's not in my budget right now. All I need is a motor and Maybe a starter box. RUSTY

 

You have a tank and pressure controls, blowoff valve, etc?

 

Yes AX I have all of that on the tank. Just wondering if the two would work together. Here they are.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93786

 

Here is the other one
http://www.harborfreight.com/cpi/cta...temnumber=7570

 

The compressor calls for a 5HP motor so I would find a 5HP, not a 3HP that has a phony 5HP rating.

 

Not to hijack the thread, but I had a general question about air compressors and more specifically the electrical hook-up necessary to use a larger one at home. Lets use the air compressor that Ax pointed out from harbor freight as an example as I was considering this unit myself...

Quote:

Why not go with this:

Will this plug into a standard household socket or will there need to be a special plug or line installed in the garage/house? I know there are such things as 110 and 220 circuits but not sure of their applications.
This compressor says "230V" ...Where does that fit in the picture?
How do I know if my house has the right electric hookup already?
If I don't have one, how do I get it and how much does it cost normally?


Probably dumb questions ...but I am clueless when it comes to electrical stuff. Thanks for the help guys.

 

Hey, clueless. Me, too. I hate electrical stuff, but this was really easy.

I bought my compressor from HF. It is a 230v, single phase, which is exactly what the clothes dryer is hooked to in my garage. All I had to do was buy and install the right plug on it and I plugged it into the dryer outlet. Yours may not have a cord on it yet, but there should be instructions on how to wire the cord to the J-box on the compressor. You can get what you need from Lowes or Home Depot.

If still in doubt, any electrician can do it in about 15 minutes...which should only cost about $140. jk

 

Ordinary househoud voltage (tv, lamps,toaster,etc) is "110" which is in fact 120 volt +/- (Mine reads anywhere from 115 to 118 most times.)

High current devices... ovens, air condtioners, hot water heaters are '210' or 220 volt. the 110 and 210 are holdovers from years ago.

there are industrial applications where 230 volt is actually correct... and as far as I know a motor that says 230 will operate on 220.

As for the 'plug' a 220 volt circuit requires a special circuit and a special plug... just like your electric stove or electric dryer.....

end of lesson electricity a.c. 101...

I'm sure there will be someone 'electrically gifted' along soon that can give you much more confusing techno talk...

john