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  #11  
Old 09-28-2016, 08:24 PM
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Mark, that compressor head would thrive with a 5hp motor on it.
I have a Quincy 325 on a 5hp 1750rpm motor at 18cfm and 150psi.
I would not hesitate to use a 5hp in 3450 rpm. Thousands may disagree, but I been there, done that, and think it was actually easier on the breaker during startup, as the reduction has to be greater.

If all you can scare up is a ordinary taperlock pulley of the correct diameter, go and borrow the fan from the bathroom and hook it up to run when the compressor is on and have it blow on the fins.
But I would try and get the real deal from Kellogg, and use the unloaders for ease of starting.
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  #12  
Old 09-28-2016, 08:27 PM
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I didn't do a thread, I have an ancient V 4 conventional compressor, that was originally powered by a 18 hp 3 phase motor, it is on a 75 gallon horizontal tank, the motor was replaced with a 4 cylinder chev industrial from an IHC swather, the engine rotation is opposite from the motor so that required mounting the engine on a skid in front of the tank. it work really well, the only part that I had to buy was the sheave insert to fit the engines output "pto"
the rest is salvage and crap I had lying around.
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  #13  
Old 09-28-2016, 09:54 PM
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Quote:
Originally Posted by Silverback View Post
So these are my 3 motor choices without going too much out of my way. Any thoughts on which one? Anyone have any idea how I can figure out what pulley ratio I can use with each one without overloading the motor???
What is the RPM of the Compressor?

2- MagneTeK- I don't remember where I got this one from. This is probably the nicest one out of the bunch but it's got a squeaking coming from the rear bell that I'm pretty sure it didn't have when I put it down there. It's very high pitched, like a piece of sheet metal rubbing, not a bearing... if I'm going to use this one I probably need to figure that out first
This sound of rubbing is from the centrifugal start switch and will disappear at speed

#1 and 3 I know are in good shape, I've used them recently. #2 is an unknown, I'm pretty sure it was a dumpster dive or something similar and I've never had it wired up.
I would choose #3 because a compressor rated motor is supposed to be set up with the capacitors for high starting torque loads...does not mean it has...just saying

The #1 Sears motor drawing 14 amps is rated at 2.3HP full load amps, don't use it.
5 HP at F.L.A. is 28amp and as #3 is not talking, #2 says it is close. #3 says 115% rated overload so it may be just fine.
I have subbed in a old 2hp motor(old means a 1.375 shaft on 2 hp) and ran it at 27 amp on my compressor so it was putting out 5hp, but as it was intermittent duty it survived and became my lathe motor.

Edit...go to this thread for a spreadsheet with a spot to plug in your drive and driven pulley sizes and rpm and get the answer to the rpm question.
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Last edited by Ironman; 09-28-2016 at 10:16 PM.
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  #14  
Old 09-28-2016, 10:26 PM
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Quote:
Originally Posted by Ironman View Post
I would not hesitate to use a 5hp in 3450 rpm. Thousands may disagree, but I been there, done that, and think it was actually easier on the breaker during startup, as the reduction has to be greater.
I am one of the thousands that would kneejerk disagree mainly because of the difficulty in gearing it down to the 600-900 rpm that the compressor will be happy with.
I too have done it before and that was precisely the problem I ran into.
By the time I got the motor pulley small enough to keep the compressor rpm down I didn't have enough belt wrap to keep it from slipping.

That's one of the reasons that used 3450 rpm motors in the 3-5hp range are usually so much cheaper & readily available.
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  #15  
Old 09-28-2016, 11:56 PM
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Originally Posted by cutter View Post
I am one of the thousands that would kneejerk disagree mainly because of the difficulty in gearing it down to the 600-900 rpm that the compressor will be happy with.
Rod, I'd agree with you at that rpm. I have never had a unit at less than 1000rpm
The quincy I have is 1200, the the triple one before it was 1400, and I have a huge Rand that is rated 98cfm output at 1100rpm.

But some of the larger single cylinder ones are down at 800 I am told.
Just looked up the Kellog and they said the pump needs 800 - 1000 rpm to generate the rated cfm, so I would run at 1000. just my way of thinking.

I found a manual here and the pump charts are worth a look. For this situation, 5hp limits the output to about half the max and between 700-800 rpm. I see a jackshaft in Mark's future.
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It is tempting to blame others for all this, especially those in control of the system, but don’t forget that for decades you voted for people who routinely lied before elections, and told you what you wanted to hear, that you could have it all right now and to hell with the future – well, that future has now arrived. Clive Maund

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  #16  
Old 09-29-2016, 05:33 AM
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Quote:
Originally Posted by Ironman View Post
If all you can scare up is a ordinary taperlock pulley of the correct diameter, go and borrow the fan from the bathroom and hook it up to run when the compressor is on and have it blow on the fins
I have seriously considered using an 8" server rack fan just wired into one leg of the output of the contactor...

Quote:
But I would try and get the real deal from Kellogg, and use the unloaders for ease of starting.
What do you mean by "use the unloaders?" Don't they just work? Do I need to do something to make them work?

Quote:
Originally Posted by Ironman View Post
I would choose #3 because a compressor rated motor is supposed to be set up with the capacitors for high starting torque loads...does not mean it has...just saying
I'm a bit amused by you feeling best about the one that has the least information on the nameplate from such a paragon of equipment like Harbor Freight.


I spent a little time digging and I can't find any information on it online either.

Quote:
Edit...go to this thread for a spreadsheet with a spot to plug in your drive and driven pulley sizes and rpm and get the answer to the rpm question.
I might be missing something, does any of that spreadsheet apply besides the part that calculates pulley ratio/rpm (which is easy enough to do with a calculator or even in your head)?

What I was concerned about with the earlier rpm question is that the more you pulley it down the more torque you have to turn the compressor shaft, and I'm wondering if say if I decided to use the Craftsman (AO Smith) motor if there is some point that it needs to be pulleyed down to work.

For that matter, the no-load rpm of all 3 of those motors is 3450rpm, I'm curious if the loaded rpm will be close or does it drop significantly like loading down a gas engine?

Quote:
Originally Posted by cutter View Post
I am one of the thousands that would kneejerk disagree mainly because of the difficulty in gearing it down to the 600-900 rpm that the compressor will be happy with.
I too have done it before and that was precisely the problem I ran into.
By the time I got the motor pulley small enough to keep the compressor rpm down I didn't have enough belt wrap to keep it from slipping.

That's one of the reasons that used 3450 rpm motors in the 3-5hp range are usually so much cheaper & readily available.
Cutter, I agree with you in general, but in practice, I have 3 3450rpm motors sitting around that should work, and no 1750.

If I can find the correct Kellogg pulley that is 13.75", a common 4" pulley on the motor (assuming no load speed) will end up at 1004rpm and a 3.5" pulley will work out to 878rpm, some pretty reasonable numbers.

If I can't find the right one compressor pulley, it seems like 10" pulleys are the most common/available and it looks like a 2.8" motor pulley is fairly common which would put me at 966 (again, no load motor speed).

If contact surface area (belt wrap) ends up being a problem I'm curious why the automotive approach isn't a more common solution, just add an idler/tensioner between the 2 to get more belt wrap?
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  #17  
Old 09-29-2016, 05:49 AM
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To take that last bit a step further, 10" 6 rib pulleys don't seem to be all that uncommon out there, though they come with bores for a smallish tapered shaft. 2.8" 6 rib motor pulleys are also fairly common (the 966rpm combination).

The HF motor actually has a 6 rib pulley on it right now since it was used to drive a alternator for an alternator powered TIG, and 1.6" to 3" 6 rib alternator pulleys are used to transfer more than 5hp all them time (If I turned up the power going to the field coils of the alternator on my welder enough I could stall the 5hp compressor motor through the 6 rib belt and a ~3" 6 rib alternator pulley).

If I ended up with belt slip I have some large automotive tensioners sitting around from when I was making supercharger kits and I'm sure I can make a bracket to make that work (the bigger issue is that it would mean spacing the motor/compressor apart which would take up more room on top of the tank)

Does anyone think that boring a roughly 13/16" tapered bore to 1" and cutting a new keyway would weaken the hub on one of these pulleys enough that it wouldn't work?
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  #18  
Old 09-29-2016, 08:47 AM
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Quote:
Originally Posted by Silverback View Post
I have seriously considered using an 8" server rack fan just wired into one leg of the output of the contactor...


What do you mean by "use the unloaders?" Don't they just work? Do I need to do something to make them work?


I'm a bit amused by you feeling best about the one that has the least information on the nameplate from such a paragon of equipment like Harbor Freight.


I spent a little time digging and I can't find any information on it online either.


If contact surface area (belt wrap) ends up being a problem I'm curious why the automotive approach isn't a more common solution, just add an idler/tensioner between the 2 to get more belt wrap?
Unloaders work by applying tank air to a piston in the unloader to open the intake valve. If there is no air in the tank they don't open as no unloading is needed. On yours and on Quincy units they use a centrifugal unloader. That means as the crank starts to turn the centrifugal valve is open, the unloaders are pressurized, and the pump does not pump. As rpm increases, the flyweights fly out and close the air valve and the pressure is off, so the pump starts pumping.
I chose on mine, to bypass that and use a timed electric relay so I control how long before the pump starts pumping. This makes winter starting easy, as I set it for 10 seconds freewheeling to distribute oil and warm up before the pumping starts.

As far as motor belts go, you would be ok with a 4" on the motor and a 18" on the pump for 766 rpm. Good luck finding an 18" pulley. I have never been able to. I owned a 24" that I had to part with...
As far as a spring loaded idler goes, it would help. I like the micro-v belts, and they consume way less power than V belts do, but unless you can machine pulleys, they seem rare. So the other option would be 2 V belts.

Does a electric motor lose rpm under load? you bet. It will drop down to 75% of the plated rpm and then the start switch will close and power up the start winding. Then the magic smoke starts to pressurize.
Any motor drawing down that much is pulling more amps then the nameplate
says and it is getting warm fast.
An ammeter to check FLA is often a money saver.

On #3 motor, if you have no other info, (and I assumed you had) then it is in the same junk class as #1. #2 at least is close to 5 hp.

I have also seen 2 of the 3450 motors ganged together on a compressor with an idler between them, but that is such a goofy looking presidential solution.....
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It is tempting to blame others for all this, especially those in control of the system, but don’t forget that for decades you voted for people who routinely lied before elections, and told you what you wanted to hear, that you could have it all right now and to hell with the future – well, that future has now arrived. Clive Maund

Even duct tape can't fix stupid ... But it can muffle the sound.
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  #19  
Old 09-29-2016, 12:40 PM
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Sometimes old ag equipment like combines can have some of those big pulleys.

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  #20  
Old 09-29-2016, 02:12 PM
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That's a good thought for me to remember, but Silverback is in DC. They only combine money around there.
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It is tempting to blame others for all this, especially those in control of the system, but don’t forget that for decades you voted for people who routinely lied before elections, and told you what you wanted to hear, that you could have it all right now and to hell with the future – well, that future has now arrived. Clive Maund

Even duct tape can't fix stupid ... But it can muffle the sound.
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