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Topic Review (Newest First)
09-17-2013 02:03 PM
infotech I'll keep in mind not to necro bump. I'm a Hvac Tech and IT Tech turned into an Energy Manager.
Just had a funny route to get where I am today. I found this site looking for info on my compressor.
I'm looking for a way to filter water out of my Crankcase oil. I'm in a humid climate and have an outside install on my compressor.
09-17-2013 12:32 PM
69 widetrack This is great information and I will file it in my electrical section. Welcome to the forum, when it comes to electrical I have always had a bit of a mind block...when I first got into the mechanical side of the trade, I couldn't screw a marette on 2 wires...now I just can't spell marette so I'm getting better...LOL

Just to let you know, the thread is 1 1/2 years old...just a heads up, I did the same thing when I first joined, but, your information is still appreciated...I take it your an electrician?

Ray
09-17-2013 11:59 AM
infotech
Quote:
Originally Posted by Old Fool View Post
Schulz website states their 7.5 hp motor draws 5.6kw@230v.
That is 24.3 amps.
24.3 amps is 3.5 horsepower.

I think Schulz and Sears have the same advertising director.
Your right till the point I embolden. Schulz's math is correct to state a 7.5 hp Motor consumes5.6 kw of power @ 230v. You are correct in saying that 5.6kw@230v = 24.3VA . I can't figure how you think 23.4VA = 3.5hp. Your math is flawed.

230v * 24.3VA = 5595W 5595W / 746w= 7.5hp their is no direct correlation between Amps and HP. HP and Watts one the other hand are direct relationships because they are both units of consumption

1hp = 746w HP is just a way to reduce the number on power consumption, just as Watts is a reduction on BTU. Sure is easier to say 7.5 horse power then to say 19,090.14 BTU 1w = 3.412 BTU 1Kw= 3,412Btu

The HP they advertise is not a simple as just the 3 numbers your using.

take my Shculz Compressor for example. My motor is rated 10hp with input voltage @ 208 ~ 230v / 460v and 29 ~ 26.8 / 13.4 amps. it has a Eff of 89.5% and a Pf of 78.
with all things being Ideal thats 230 x 26.8 X .78 x 1.732 = 8327w / 746w = 11.16 hp 11.16 X 0.746 / 0.895 = 9.30 HP

11.16 hp + 9.30hp = 20.46 / 2 = 10.23HP is the rated HP


Formulas:
Watts single phase. V x A X pf (power factor) = watts
Watts three phase. V X A X pf X 1.732 = watts
Motor Input HP. W / 746w = Input HP
Motor Output HP. Input hp x 0.746 / Motor Efficiency = Output HP
(this is also called Motor kW and is how things are rated in Europe.)
Motor rating Input hp + Output hp / 2 = rated avgerage.


Oh and since I have a shculz I'll let you know they are a great compressor. Sorry for the derail.
12-11-2012 11:57 AM
boatbob2
Wiring..........

The National Electric code,is minimun wiring recomended,i ALWAYS go down to the next LARGER spec wire.Never had a problem........
12-10-2012 11:43 AM
loctite
air comp

Its working great!! Not to loud and pumps air up fast!! I use it about everyday as I restore cars. I can use 2 DA sanderas at the same time with no air drop. One da sander used 11.5 cfms My comp is rated at 31 cfms. 7.5 hp 80 gal tank and 2 stage. Hope this helps.
12-10-2012 10:57 AM
1967SS project
Schulz Air Compressor

I wanted to check to see how your air compressor is working out for you?
I'm thinking about the same model and manufacturer. Is it very loud?
03-24-2012 02:31 PM
loctite
compressor

The compressor came with a auto drain. Heres the deal . I found this compresasor on craigslist just north of me. It was brand new. The man had bought it for his shop but passed away before he could install it. His son wanted it gone. It had the auto drain and magnectic starter box and a gallon of oil with it. all for $1100. So far so good. it runs quiet and pumps up fast.
03-23-2012 11:27 PM
vige Randy,

Congrats on the compressor! I am glad that it looks like a great compressor. I will wait to hear how it turns out and probably order the same one. It really does look like a nice machine and at 39cfm, it ought to be able to power a decent size sandblast cabinet. Let us know how it turns out.

Geert
03-23-2012 03:20 PM
Old Fool
Quote:
Originally Posted by loctite
OLD FOOL!! So you are saying I need to have a 60 amp breaker and #6 wiring? I will have to check to see what my old compressor has. but i know it has a 30 amp breaker that I will have to change out. My compressor is right next to my breaker box so i will only need a few feet of wiring. Thanks for the help.
I just posted what the National Electric code calls for.

Yes the 30 amp wont cut it.

A short story, years ago, 1992 to be exact I had a fire in my garage. It pretty well burnt the garage down. The insurance company had a fire investigator come to determine the cause.
I never heard a final report, but what I do know is the investigator cut the electrical panel loose from all the wires and mast and he took it with him.

Had there been any undersize wire in relation to any breaker it was attached to, I am sure they would not have paid to rebuild and refill the garage.

If you have a short run , a bit of #6 will be cheap, you will have a 50 amp circuit if ever needed, and the starting of your compressor shouldn't experiance much voltage drop.

Better safe than sorry.

That compressor will last you a lifetime, a very nice purchase.

I do suggest you put an auto drain on the tank so that nice new dry clean tank stays that way.

I am to old to remember to drain a tank daily, my auto drain does it for 2 seconds every 10 minutes the compressor runs
03-23-2012 02:21 PM
loctite
air compressor

OLD FOOL!! So you are saying I need to have a 60 amp breaker and #6 wiring? I will have to check to see what my old compressor has. but i know it has a 30 amp breaker that I will have to change out. My compressor is right next to my breaker box so i will only need a few feet of wiring. Thanks for the help.
03-23-2012 02:18 PM
loctite
air compressor

I just got back with the compressor and it looks to be everything I wanted. It looks to be heavy duty. It sez in the book that came with it 32amp draw. Only time will tell if it is any good. I will keep you posted.
03-23-2012 11:50 AM
vige This from the site describing the Schulz in question:

"NEW 7.5HP 80 GAL VERTICAL
POWDER COATED - TWO STAGE AIR COMPRESSOR
1 YEAR WARRANTY ON THE CAST IRON PUMP - 30 CFM DISPLACEMENT
32 AMP DRAW 230 VOLTS SINGLE PHASE ELECTRICAL MOTOR
INCLUDES INDUSTRIAL ELECTRICAL MAGNETIC STARTER BOX ($400 VALUE)

This could be a good deal then for 1400-ish?

Old Red, can I get away with a 40 amp breaker? Running out of panel--I set in a second panel rated 100 amp, but already have 2 30 breakers running. One 30 amp for 5000 watt garage heater, one 30 amp for AC.

Thanks,
geert
03-23-2012 08:47 AM
Old Fool
Quote:
Originally Posted by loctite
The schulz compressor is made just north of atlanta ga. They have been thier for a lot of years building these. The amp draw on the 7.5 is 33 amps. Its 30 cfm and 80 gall tank. I have a 5 horse 60 gallon 13cfm and it will not run my blast cab. Nor my buffer. It can't keep up. I just bought the schulz compressor 7.5 today and will be picking it up tommorow. If you do some reading on it and also go to the home page it sounds like a real good compressor. Check out the web site schulz compressors. Hope this helps. Randy
Interesting you have documentation that says 33 amps.

The Schulz information I found on the Schulz website says 230v 5.6kw.

Divide kw by volts to get amps.

Maybe the info I saw is a typo, 7.6kw would be 33 amps.


Either way 33 amps will do a lot of work for you.

Run wiring large enough to operate it will be a few more dollars!

The NEC (code) requires that the table 430.238 be used to determine the wire and breaker sizes.
For a 7.5 hp 1 ph 230 volt motor 40 amps is listed in the table.
A load factor is then applied to the 40 amps. 40 X 1.25 = 50 amps. Per table 310.16 - #6 wire is required.
A minimum (nominal) breaker is also 50 amps but can be increased to a maximum size of 100 amps.
For the purposes of the compressor a 60 amp breaker should be used.

source: post #5 http://www.hotrodders.com/forum/new-...ze-211285.html
03-22-2012 10:25 PM
vige Oh hey! Randy...you actually bought one and are going to use it in the days to come? Awesome. This is exactly what I was hoping for...better really; a first hand account from someone who actually works with it for the same type of application. Please post us some of your impressions when you first get the compressor, and after you have had a chance to work with it.
I have a hunch that this compressor is really good deal for the money--obviously so do you.
Geert
03-22-2012 09:43 PM
loctite
schulz compressor

The schulz compressor is made just north of atlanta ga. They have been thier for a lot of years building these. The amp draw on the 7.5 is 33 amps. Its 30 cfm and 80 gall tank. I have a 5 horse 60 gallon 13cfm and it will not run my blast cab. Nor my buffer. It can't keep up. I just bought the schulz compressor 7.5 today and will be picking it up tommorow. If you do some reading on it and also go to the home page it sounds like a real good compressor. Check out the web site schulz compressors. Hope this helps. Randy
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