Wiring elec motor for 220v..


Old 07-16-08, 12:56 PM
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Wiring elec motor for 220v..

Hi... I have a post over at (Tools, Sharpening and Power Machinery) Entitled (New Air Compressor not performing).
If you want to catch up on what this is about....
I've had one reply in 24hrs...
The gist of the post is,me asking about my new Air Compressor,and it seemingly running much slower than the 3450 rpm,that it's rated to run at.. The particulars can be found at the post area.
I'm writing here about the one reply I received,trying to get some idea of verification on the members reply...
I stated on the original post that the motor is wired for 110v @ 15 amp.
The motor can be wired for 220v.
The member replied that maybe,the motor has been wired for 220v.
I could see this possibly happening via human error,from the factory.
I'm not an electrician,and wouldn't know what I was looking at after removing the cover plate to check the wiring scheme of things.
My post here is to confirm the idea that this is possible.

What I mean is....
Is it possible that the motor would run at all if it were wired for 220v,and connected to 110v ???
It does seem to me that the motor is running at about half of the rated rpm.
If you are familiar with what I mean by (a slow runner) air compressor.
By this I mean in the days of old,most good quality air compressor motors,ran at about 1800 or a bit faster..
Lately (last twenty) years most have gone to much faster motor speeds.
I've owned small compressors that turned at higher rpm's in the 3000 range,and this one is rated for 3450....
I can tell ya... it isn't running at that speed..not even close.
I can actually see the spokes in the small pulley (on the motor) turning...
If it were running at 3450,it would be just a blur.
All of the spec particulars of the compressor,are on the other post..
I'm here just to try and find out if the motor would run,albeit slow if it were miswired for 220v....
I actually hope the answer is (Yes)...
Maybe I'll find that that is/was the problem.
Thanks for any reply.
Old 07-16-08, 02:46 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
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For those that want to read the original thread:


You have received good answers. Yes, it is possible that the compressor was mistakenly wired for 240 volt operation and that is easily determined by removing the cover from the connection box on the motor and comparing the connections with the motor nameplate.

It is also possible that the compressor or motor is just plain defective.

Check on the wiring connections first and post back.
Old 07-16-08, 06:06 PM
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Hi Furd

Hi,Furd .....
Thanks for the reply.....You help out as usual.
You helped extensively with a shop wiring for 220v,back last year,or the year before...
I couldn't have ever done it without ya.....
Everything worked out just fine with that project.
So far nothing has burned down,and all is working to my likings.
Here's just another thank you,and I hope all's well with you.

Well....... Sense I posted this,I have gone out and looked at the wiring connection on the compressor motor....
There is a worded and numbered chart on a sticker that is on the motor.
It's about a 5"x8" and easy to read ....

It just simply states wire (colors) and they are placed by a vertical number ... The numbers are 1,2,3,4.
For 110v it has the color/s aligned beside certain number.
Then for 220v it shows color/s beside diff numbers..
I can understand the printed version and what it represents.

However removing the cover plate from the rear of the motor,shows no indication as to which connector is supposed to coincide with which number.. ...... !

Stop..... Hold it .... Or I thought that to be the case.
I couldn't see any numbering system marked at all..
I decided to give it a good Furd attempt...
I went in and got my 3 cell Max Light,and my trusty big lens 4x glass ....
Putting good light,and closer vision to use....
Sure enough there are numbers stamped at each possible connection point.

So looking at the drawing... I find that the motor is indeed
wired for 110v.....
To set it to 220v... you just move one wire to a presently unused post,and swap out two others..

I guess the good news is,it is setup for 110v.
The bad news is,this compressor won't even keep up with my small 1/8" orifice blow gun...
Or that is,not at 90 psi it won't...
This thing is rated to deliver 5.5cfm @ 90psi. --
4.5 cfm @ 125psi.
It won't stay up with my blow gun till it drops to 70 psi.....
I wouldn't think this blow gun could discharge nearly what a 1/2" impact would.
I bought this compressor for the twin cylinder,and 3450 rpm motor.
Thinking it surely would deliver the goods..... CFM wise.

As I said in my original post elsewhere,maybe I'm expecting too much !
Also mentioned on the other post,was the fact that at running speed,at the intake orifice,there isn't even enough suction to even pull your fingers to the opening.
A small 1 horse vacuum cleaner sucks more than this thing does.
I mentioned this to the warranty folks at Speedaire,when I called them...
They asked me if I ran it for the recommended 45 mins,at no load (air vent open at tank) so the rings could seat ??
I answered no !
It doesn't say to do this in the manual.
In any case,before I call Grainger,asking where they want me to deliver this thing for refund.
I suppose I could let it run as suggested and see if it gets any better....as far as CFM output goes..
I really doubt it will........
Another thought....would be to go to a larger motor output pulley.
There is a 10" (air moving)flywheel type pulley,on the pump.
There is a small 2.5" pulley on the motor shaft.
These are dia measurements..
2.5" seems really small.......
I'll have to check the running amp load,and if I have room to play with,I'll add a larger pulley...
More speed at the pump.
I've got 10-30 Mobil 1 as compressor oil,this is what Speedaire wanted ....
In fact they said "Not to use regular compressor oil."
You don't find this out till you get it home.
This sounds like padding of poor components to me.

In any case.
I have this connected at one of my outside GFI outlets,that are 20amp models,wired with #12.
So I don't see startup as being a problem....
To really be fair.....about this...
I guess I'll first connect up my largest air tool,a 1/2" impact,and actually see how the compressor performs,with the impact full running.
If it'll hold 90psi,at full impact discharge.
Well maybe I should be satisfied.......
It may just be that my blow gun,is indeed too much of a air hog.
To try and keep from needlessly beating up on this compressor on here.
I'll post back with my findings,as to the 1/2" impact test results.
Experience = The test always comes before the lesson !
Thanks Furd
Old 07-16-08, 07:35 PM
Join Date: Mar 2006
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Air compressors are somewhat my specialty although I consider anything of less than 750 CFM to be a "small" compressor.

I have a feeling that you are not going to like this but an 1/8 inch orifice at 90 psi will flow almost 24 CFM. Even at 70 psi it is flowing almost 20 CFM. So with that information it is certainly to be expected that your 5.5 CFM (at 90 psi) compressor can't maintain rated pressure.

Your 1/2 inch impact wrench is "rated" at maybe 4 or 5 CFM "nominal consumption" but that takes into account that you do not run the wrench continuously but in bursts with a waiting time between bursts. More likely as not your wrench consumes in excess of 20 CFM while operating.

When you look at the pulley on the motor is it being illuminated by a florescent light? If so, then that explains why it looks to be running slow.

Do not change the motor pulley size. While that will speed up the compressor pump it will also increase the power needed to turn the compressor and THAT will cause the motor to burn out. Home shop compressors have special motors that are rated to be run intermittently at high overloads. They DO NOT supply their "rated" horsepower on a continual basis. The actual horsepower of that motor is probably somewhere around 1-1/2 horsepower.
Old 07-16-08, 09:21 PM
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Furd... It looks like I'll keep it.

To start with,I guess I'll can the idea of a larger dia pulley.
Even though I'm sure the motor will run with a bigger pulley.
It just very well,could be detrimental to the life of the motor.

I had already considered the idea that the blow gun was just too air hungry,in what it would dispense.
So.....the air gun being allowed to run wide open,and checking the ability for the compressor,was just a lark of a test....
After all,I don't have 50HP motor and a 200 gal tank,running on 440v.
It had no real basis in the real world of air and tool use and requirements.
However as stated,the compressor did manage,to hold even with the air gun discharge @ 70 psi.

I then went and got my most air hungry tool.....1/2 impact driver.
I determined that at 125psi the compressor would indeed supply the needs,as far as real world use would be realized.
Meaning the compressor kept up well enough in my opinion,
as far as any real use that I would ask of it via this impact wrench...
After all,I doubt I'd have the impact wrench wide open for mins on end,with no stopping.

By the way..... The blow gun,did dispense much faster than this impact wrench..... Now we know.....

I had called the Speedaire warranty center earlier on,to insert my findings about this compressors CFM output,and to see what they had to say.
I was asked if I had allowed the compressor to run,for at least 45 mins total with no load (tank dump open) to allow the rings a chance to seat...
I answered (No)....
The manual didn't say anything about doing this..
However it does seem to make sense.

So today,I let it run,for 25 mns,non stop.
2morrow I'll let it run again....for 25 mins.
I'll try to ascertain as to if this made any diff,in performance.
If it doesn't kill it.
I still think it should have more suction at the intake,than it does. .......... but
In any case....finding out that the motor is wired correctly,at least eases some performance questions.
It did do ok,with the 1/2" impact..
It took a good long blast,to kick the motor on.
Far longer than I'd ever actually expect to have the impact pounding away at some work.
At 90psi it did even better.....
After all of this I've just about done a performance review,on the Speedaire 1nnf6 model.
At startup (MT tank) it takes about two mins,to pressure up to cutoff @125 psi. This is a 20gal tank.
Also ... I find it somewhat noisy... that's a high somewhat noisy..
There seemed to be lots of intake breather noise,that I thought was as loud,if not more so,than everything else.

Another thing I noticed... thats off topic,some more.
Is the fact that,after the 25 mins of steady running.
The oil sight glass,now shows some pretty dirty looking oil.
As mentioned originally,I have a 10-30 Mobil 1,in the pump crankcase,so I hope that after my next shot at 25 mins of continual running,the oil doesn't get as dirty,as fast.
I'll change the oil,after the next 25 min run.
Just to be on the safe side of having oil contaminated with metal.
Something I didn't expect,was to see the oil that dark dirty looking.
It looks like a motor oil at 6000 miles or more.
I have no idea where the discoloring came from.
That is,I mean there is no carbon from fuel combustion per se,so I'm a little shocked.......

A point to mention..The compressor arrives with no oil,or very little.....just a smidging,for transit coating.
I removed the drain plug before adding the original oil,just to have a look,and there was very little run out.
However it was clean pretty oil.. My point the oil in the crankcase before the 25 min run,wasn't dirty looking at all.

As I stated,I'm hoping that as time goes by,the oil doesn't show so much contamination so fast...
I'll be doing a magnet test,with the old oil just to see what all it comes up with.

I really don't understand though,why the oil is so dark burnt contaminated looking.

There's no way it got hot enough to actually burn the oil,(my gosh it's Mobil 1) but then what has caused the dark,obviously contaminated discoloration.... ?
The head was hot (as expected),but not that hot,180 maybe.
Too hot to keep your hand there,but wouldn't have ever boiled water.
Ya see....now I've opened another can of worms.
Maybe it's from some kind of rust preventative coating from the factory..... I just hope it's not from rust.
I personally don't think it to be from rust.
That's why I mentioned how good the oil looked that was in the crankcase from the factory.

One plus,Is that on the plate on the motor,under (Duty cycle.)
It states "continuous" ....
I hope it holds up.

In any case .... we live and learn.
It looks like I'll be keeping the compressor.

It's even got the cool looking expansion fin tubing,that fits over the delivery tube,from head to tank.
Added effort at cooling the air,before the tank.
It doesn't show this finned tubbing in the photos,of this model,but it's on there.
Old 07-17-08, 12:10 AM
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Furd .,, Looks like we do like play with big " toys " lol

Anyway let get back to the topic for a min related to the air compressor motor.

A golden rule with piston compressors is never upsize the motor pully without verify the current drawage.

The only way to verify it is use the clamp on ampmeter to check the current drawage vs the nameplate rating.

The reason why I mention that due some of compressor is designed for either 120 or 175 PSIG range and the factory will sized the recomend motor hp and pully size the only time you can increase pully size if the following cireca { details }

Compressor Max RPM { you may have to get ahold of the manufacter for the details due tons of diffrent size compressor have diffrent ratings }

Max CFM setting.

Larger motor { only if the manufacter spec'ed to say ok for larger HP / CRPM { compressor RPM }

there are few others details depending on the type of compressor set up.

Yes all compessors will get very warm during hevey useage.

They can hit much as 250F some case little more on air cooled compressor. Watercooled compressor will be lower but it depending on the set up.

In my shop I have 15 HP air compressor with water intercooler with double 120 gallon tanks and it only took about 1 1/2 to 2 1/2 min to full charged the tanks.
The current drawage is no where the limit of the motor but I can speed it up but I rather not to due it fill up the tank so fast so I leave it alone.


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