homemade air cmopressor information

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Old 07-07-07, 07:53 PM
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homemade air cmopressor information

i bought a 5 hp compressor pump with about 14 inch flywheel
and a GE 5 hp 3450rpm 220 single phase compressor duty motor

i put a 5 inch pulley on the motor ive use it a week not a problem untill today i used it all day and at the end the motor just buzzes like the start capacitor went bad this motor is a week old the capacitor was warm but not hot

i guess my question is... Is my pulley size is correct and how do i test my capacitor or do i just return my motor and try this again hope you can help me tom
 
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Old 07-08-07, 04:22 AM
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You need to know what RPM the compressor is suppose to be run at.
Then use it and the RPM of the motor, plus the size of the compressor pulley to accurately determine the size of the pulley that goes on the motor.

The motor itself may not have been rated for continuous duty and simply burned out from being ran to long without a cool down period.
 
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Old 07-08-07, 05:47 AM
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Pendragon is right in that you need to know exactly what speed the pump must turn to be driven by a particular motor.
You are spinning the pump at around 1200 rpm which is pretty fast and approaches max rpm for many compressors.

When assembling a compressor, even with the mfr's information you need to use a clamp on ammeter to check the amperage draw of the motor at the highest pressure before shut down.
Another thing is that if you have the cut out pressure too high you could overload the motor as well.
A 3450 rpm motor is not a heavy duty motor compared to a 1725 one and is more sensitive to being overloaded.

Also, the purpose of the air tank is to control the cycling of the compessor and if too small will short cycle while in use and heat up the motor as well.

What make and model pump do you have and if you are able to take a picture and post it on a site like photo bucket we could take a look.
 
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Old 07-08-07, 07:11 AM
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more info about homemade compressor

Originally Posted by TomKirsch1974 View Post
i bought a 5 hp compressor pump with about 14 inch flywheel
and a GE 5 hp 3450rpm 220 single phase compressor duty motor

i put a 5 inch pulley on the motor ive use it a week not a problem untill today i used it all day and at the end the motor just buzzes like the start capacitor went bad this motor is a week old the capacitor was warm but not hot

i guess my question is... Is my pulley size is correct and how do i test my capacitor or do i just return my motor and try this again hope you can help me tom
max rated rpm for compressor is 1200
im not sure what im exactally running . how do you find this out

also when i take the belt off the compressor the motor runs and the compressor spins by hand

max pressure on on switch is 125 and i set the motor to turn on at 100 psi takes 30 secs to fill tank is this correct i will try to get pic the compressor pump was from harbor freight it a v twin type and is rated for 5 hp motor and thats what i bought
is this right and when it runs it only
 
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Old 07-08-07, 11:34 AM
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You are pretty close on the RPM's, assuming the motor can do 3450 loaded.
If that's no load RPM, then you're fine, if it's loaded RPM, drop down to a 4.5 or 4" pulley.

What size tank do you have it on?
You might consider getting a larger tank whatever it is, 30 seconds isn't a very long run time.
5-15 minutes would be better.

Here's a very nice belt/pulley calculator:
http://www.gizmology.net/pulleysbelts.htm
 
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Old 07-09-07, 06:07 AM
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Originally Posted by TomKirsch1974 View Post
also when i take the belt off the compressor the motor runs and the compressor spins by hand

at that point, discharge all the air and see if the motor can turn the pump.
if so, it could be your pilot valve not working and your motor is trying to start with head pressure in the pump.
 
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Old 07-09-07, 09:37 AM
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Flops got a good point and I hadn't thought of that, you probably need an unloader valve in the mix.
 
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Old 07-15-07, 08:59 AM
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up date homemade compressor

hey guys

i do have unloader valve it works
i took motor back upgraded to 6.5 horse it worked a week and did the same thing . soooo now what its either crappy motor or pulley size issue

motor GE 6.5 hp 220 compressor duty 3450 rpm

compressor pulley 13''
motor pulley 2.5
distence between motor shaft and compressor shaft 13.5 ''

is my motor pulley size burning my start compacitor ?????
 
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Old 07-15-07, 11:15 AM
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A picture would sure be nice.

There is something missing here I think.
What is the story on this thing?
Are you repairing an old commercially made unit with new parts, is this a new build with an assortment of different components, what exactly are we looking at?

You say there is an unloader.
Is it a pressure switch with an unloader valve on it?
If so it should release just before the it closes to start the motor.
There should also be a check valve in the discharge line at the tank so it is between the compressor head and the tank.
When the air is released it should just give a short burst of air to release the air in the line and head.

Is this happening?

You can test this by allowing the tank to build up pressure and allowing the switch to cycle the motor off.
You can then unplug it and then slowly bleed the pressure off until the switch clicks.
At this point there should be a short puff while the air releases.
Some switches only momentarily activate and you can further check to make sure the line is void of pressure.
You can CAREFULLY and SLOWLY loosen the discharge line at the head to make sure there is no pressure at the pump.

Also, you have not said how big your tank is...............too small will short cycle which is very hard on those two pole 3450 rpm motors.
These motors are not as heavy duty as a comparable hp in a 1725 motor.

How about the voltage at the motor.
Is your wiring adequate?

Not directly related to your problem do you have a pressure relief valve on there that is rated for your pumps flow rate?

I assemble and work on small compressors as part of my job and really, for what you are doing a clamp on ammeter is the only way of properly troubleshooting this.
If you had one you would likely could have sorted this all out with motor #1.

You might be finding out by now that with the price of air compressors these days it really does not pay to build them yourself unless building them is a hobby in itself.
I have built dozens and at one time it would pay but now this has gone the way of building your own speaker cabinets.
 
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Old 07-15-07, 02:44 PM
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more info about homemade compressor

I got a sanborn 60 gallon compressor tank because it had a bad compressor with no motor . so i bought a compressor pump from harbor freight and the motor from tractor supply.
i also bought a checkvalve to go between pump and tank. this check valve has a compression fitting for the blow down valve. my blow down valve is on my pressure switch . and it is working properly .

This motor worked for a week perfectally for a week the motor would run fill the tank up to 120 psi. the pressure switch would trigger the motor to stop and that would trigger the blow down valve to take head pressure off the pump . now its ready for the next cycle.

I checked voltage at motor but not hooked to the motor im getting 240 volts is that too high???

do you reccomend me to buy a 1725 motor ? if so what size pulley on motor
pump has 13 '' pulley max rpm is 1200 .
 
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Old 07-15-07, 03:12 PM
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This is annoying but I believe it could be a very simple problem.

No, what I recommend is that you take it to the next level and purchase a clamp on ammeter.
Right now we are only guessing as to what is wrong.

You need to know what the mfr of the compressor recommends as to how the motor hp relates to the rpm and pressure.

240 volts is ok but you should check it while the compressor is running and just before it cuts out.
This is the same time you would check the amperage because it will be at its highest just before it cuts out.

You say that the unloader on the pressure switch works but have you checked to be sure the line is empty.
Some switches open and stay open once they trip but I have seen one that only vents for a brief moment and if your discharge line is too long or the check valve leaks you will still have pressure at the head.
You say it is cutting out at 100 psi but have you confirmed that pressure with another gauge............maybe it is cutting out at 150 psi?
Is the line discharge line going to the tank big enough?
A clue to this is how hot the head gets when running continuously.
They do get hot but should not discolor the paint.

Another thing is to check to make sure the motor is wired correctly.
If dual voltage it could have come wired for 120 volts which would last about how long yours have been going.

What exactly is the application by the way.
Is this used continuously and daily?

Like I said, there must be something simple going on here and an ammeter is what will help narrow it down.

Here is one:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95683

To use it you carefully separate one of the supply wires and clamp the jaws around it.
You then start the compressor and can then watch the amperage climb as the pressure rises.
You then compare the reading you get with the one stamped on the motor.
It is always good practice to have the running amperage about 10% under the rating.
 
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Old 07-15-07, 03:16 PM
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more info about homemade compressor

thank you for your insight can i get your email to send you pics of my compressor????
 
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Old 07-15-07, 04:19 PM
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A way to use pictures here is to subscribe to a free photo host like Photo Bucket, post them there and then give us a link to them in another post.
 
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