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Thoughts on compressors

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oldsparky

oldsparky

Member
Feb 15, 2018
1,148
155
arizona, United States
I was reading a post here about a compressor that made me think. Some of the compressors we use have auto pressure switches that shut off the motor when a desired pressure is met. Then the compressors ask's to be ran for a time for cool down.

A problem I see is when a motor is cut off in a loaded condition there is immediate heat build up. It would be better if the motor continued running in a no load condition before being shut down. This could be done simply by shutting the bottle then opening the dump valve. Industrial HPA compressors I have worked on use solenoids to unload before shutting down, but we could do the same thing manually by closing and opening valves. 



Another problem I see is compressors advertised to run on household voltage. A lot of 120 volt house receptacles are on a 15 amp breaker wired with 14 gauge wire. Remember there will be a current spike at start up and at loading. Some of our house circuits have multiple receptacles and lights on a single breaker. So we may have nuisance trips. Also consider the length of wiring. There will be a voltage drop the farther you get from the breaker. Especially if a extension cord is used. As voltage drops, amperage goes up, amperage is directly proportional to heat. If your voltage goes down your motor begins to heat. 



I hope I didn’t write this confusing. Anyway maybe someone can use the information.



Sparky
 
I do not have auto shut off. I bleed moisture from mine a couple times in one run, and I will periodically monitor the temp, and pressure.

I would not trust an auto-shutoff anyhow, and feel much better keeping an eye on the unit while in operation. I'll walk away from it, but come back in a few minutes. Never out of earshot of it.

As for the 120v. Find a good circuit to run it on in your home. That's it.
 
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It's all a 15 amp circuit can do not to blow on start up with the Yong Heng as it will draw 18+ amps for a short while. I run my Yong Heng on a 20 amp circuit and the only other thing that runs on that circuit is my AC unit. I do my best not to run them both as the circuit blows in a few minutes if I have them both on. 

I bought an auto shut off unit so I can set it a bit higher than my intended fill pressure in case I space out and leave it running. That way it will shut off by itself without undue stress on the unit.

I only run my YH for a few seconds after I bleed the pressure and moisture before turning it off as the water pump continues to run to cool the second stage piston and cylinder and the first stage has a cast iron cylinder and metal rings so the extra heat they get is not going to do much.
 
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What is the insertion loss and resistive loss of Romex 14/2 from a 15 amp breaker 10' from the panel extended to the compressor with a 12/2 braided extension cord that is exactly 25' in length drawing 1350W? Would this cause a nuisance trip? Thank you!

I purchased a warranty on my extension cord and highly recommend it!
 
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Ya know as I wrote the part about "heat" I was not even thinking about the compressors with water cooling. They may be fine with the compressor motor shutting down, leaving the water pump running. But the oil lubricated seems would need to stay running a few minutes under no load

Click to expand...

Believe it or not, the rotating assembly does not get very hot at all. The primary cylinder is air cooled. I have a larger fan on mine. I kid you not the airflow across my primary cylinder is roughly 4x that of factory if not more. So, the cylinder does not get hot at all either. The secondary cylinder walls actually stay cool when I hook mine up to a fresh water source. Instead of using the dedicated reservoir. But the secondary cylinder head will get a lil toasty. But honestly still not all that hot.

I forgot to mention I leave my water pump running on mine on shutoff. 
 
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(Copy and pasted not my calculations. I am being lazy.) 

In general, satisfactory motor performance requires a voltage within ± 5% of its rated nominal value in steady-state operation, Starting current of a motor can be 5 to 7 times its full-load value (or even higher). If an 8% voltage drop occurs at full-load current, then a drop of 40% or more will occur during start-up.





Using a voltage drop calculator with the following inputs.

120 volt single phase AC 14 gauge wire with a 15 amp draw at 75’ we get a voltage drop of 4.74%



Now let's say your line voltage at your house is already a few volts low and thats not uncommon. Can you see how you can get into a voltage drop situation. Or if you are adding a extension cord. You may not have a voltage drop. But I have read multiple posts of humming motors. As a 40 year industrial electrician the is the first thing I would consider is a voltage problem. A lot of the compressors that we can buy are built fragile, they are not over built for sure. If we can be as careful as we can with voltage and cooling we may be able to make them last a little longer. 



To me its a shame to spend a thousand or over more on a compressor to have it fail. If its possible to use a designated circuit I think we would benefit. That is what I do. 

Just thought maybe this is an area where I could help.



spelling edit. 




 
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