Motor soft starters and VFD for off grid

I already have a gasoline air compressor.
This is to supplement the air produced by the gasoline engine, be a backup or allow me to run 1 engine, the generator. The worse thing about electric air compressors is the start up surge.

The electromagnetic clutch I have is a daton rated for 15ft.lb. and 4000rpm. This motor is 6ft.lb. at 1,800rpm. This clutch is for "industrial applications" I think it can handle it.
It will wear out eventually like the clutch on a vehicle A/C compressor, but it will take years.
The go cart clutch on the gasoline air compressor stays engaged when the unloader opens and the engine throttles down. On the electric motor it will see some wear each start. Since the gasoline and electric compressors have the same size shafts I will just keep a spare go cart clutch on hand.
The way I figure it is that its better to have an air compressor with a on clutch on it that will eventually wear out rather then have an air compressor you can't use because plugging it into your generator kills it or messes up other stuff running on the generator.
I have a time off delay relay that will allow me to run the electric air compressor unloaded from 0 to 60 seconds, that will allow it to cool off and reduce voltage spikes when the compressor cuts off.

I have only every used ingrasol rand synthetic oil air compressor oil. It was like $50 or $60 just for a gallon. The IR reciprocating compressor oil isn't 20w, it's real thick more like chain saw oil.
All my little air cooled gasoline powered engines get 10w-40 mobil1 motor cycle oil made for air cooled engines.

I replaced the stupid 100% failure rate plastic body foam air filters that came with the air compressors years ago with metal body paper element filters and glued the housing and element together with RTV since the air filter vibrating loose and letting all the dirt built up around the filter in at once seems to be a common cause of compressor failure. I moved to NM in 2011 that was about the time I switched to bigger paper element air filters.
Yesterday we had 14% humidity and that is perfectly normal. I don't get a lot of water but I usually open the drain valve and let all the air out when I am done with them.

 

Got the electromagnetic clutch played with and on the motor.
The clutch has an inrush of 3.6 amps. The OEM data sheet say holding current should be 0.4 amps. I was getting 0.7 amps and a low power factor. So I added a 7.5uf capacitor to cut the current in half and doubled the power factor. It only saves about 100VA but that's a lot off grid.
Now I wonder what the clutch inrush and compressor engagement surge will be together.
I'll admit I did not consider clutch inrush at first, oops.

 

Hat's off to you ,splitting hairs ,making it work .
The problem I have with getting too close to the vest is that the more finely you tune something the more critical all otter factors feeding the machine are all the more critical . Like Scotty said , the fancier they make it the easier it is to mess it up.
Working on a lot of equipment through the years it's true more often than one might like to believe.
You may have to add a magnetic starter for protection, if there is a voltage drop due to a failure up stream .
though it may sound ridiculous, you've already lot invested in this project.
Good education however.
Years ago I custom built a compressor unit with both gas and electric motor ,the pilot control operated unloaders in the compressor head so that it would free wheel while unloaded and the engine would throttle down. if one were to want to run off the electric motor the belt had to be removed from the engine pulley. It was not known that there were clutches at that time that fit that job.
On another project I built a compressor that the gas engine was shut off with a pressure switch and restarted as well. all automatically .
The customer was completely in love with it.
He did welding in a bucket on a boom .

 

I have a magnetic starter on the 1hp 4 pole motor.
I have found a manually reset under voltage relay for $50. But I have not purchased them yet. The under volt relay could save the compressor motor and generator.
The only one that won't need a magnetic starter or under voltage protection is the one on the VFD. Since all that is built into the ABB drive.

I would like to alter the gasoline compressor to shut off once it's reached pressure. For when I just need air one time such as for filling a tire, dust removal or to shoot nails. With a big tank I can shoot a lot of nails before needing the compressor to run again. It would just have a manual restart nothing real fancy.

This will be applicable to most things you could use a single phase motor on.
I'll make my final repot in a note topic detailing cost to implement, how well it works, weaknesses and how difficult the install might be plus limitations, expected life span, safety and other possible applications.

 

I put my go cart clutch on a 4 pole motor today and as I suspected 1,800rpm is not fast enough to engage the clutch even a little.
So I went to Lowes and got some screen door springs measuring 1/4 of an inch.
Since centrifugalforce increases by the square as speed doubles. That means stretching the spring that came on the clutch won't work at all, to engage the clutch at half speed I will need a spring a lot weaker than the original.
I'm guestimating the K constant of this original clutch spring is some where around 25 to 30lb per mm that's what it feels like, I didn't measure it with actual instrumentation, there isn't really any point since I can't get exactly the correct spring. So I want a spring with a K constant that has more like 5 or 6 pounds per mm.
So trying to reuse the old spring will not work.
The screen door spring I got from Lowes feels like it's around 3 to 4 pounds per mm. Close enough.
I put the 2 screen door springs in the clutch and it worked pretty well at 1800rpm. I think the constant is correct but I used 2 springs and stretched them, so the spring force may have been too high. I think the clutch may have been slipping a little. I'm going to try adding part of a 3rd spring.
The results were the resprung go cart clutch lowered inrush current to almost what full power starting the unloaded 1hp 4 pole motor is.
Replicating the result I had on the 2.5hp 2 pole motor.
Which would mean going from 15 amps to 8 or 9 amps.

 

Now if you could implement a clutch used in automotive refrigeration ,it might simplify what your trying to do.

 

I already have a dayton electromagnetic clutch on my 2hp 4 pole motor.
No point in adapting an automotive one since the Dayton clutch bolts to a 56 frame motor, accepts the motors keyed 5/8 shafts, costs about as much as a vehicle A/C compressor clutch, uses 240vac power and I can put any size pulley on there that has a 5/8 keyed shaft.

 

Got the "3hp" v-twin 11.2cfm compressor on and the 2hp 4 pole motor and clutch only problem is I need a much larger 56 inch belt. I have always been able to use 45 to 48 inch belts on everything for interchangeably.
Well turns out these belts last a really long time.

 

I'll look through my belts . what groove ? A,B,C,D, 1/2" 5/8" ???

 

Just needed a 4L560. I ordered one from some where in texas, should be here in a few days. It was only $13 including shipping.

 

curious how that works out for you.

 

I got the belt and magnetic clutch setup going on my 2hp 4 pole motor.
Full power starting the motor on the compressor would use around 16 or 17 amps. That's a huge reduction compared to full power starting the 2 pole 2.5hp motor that had a 45 amp starting inrush.
So just switching to a 4 pole motor and a bigger pulley will be more effective than anything you can do to soft start a 2 pole motor.
Free spin full power starting the 4 pole 2hp motor uses about 13 amps.
Resistor starting the motor uses about 10 amps, I may be able to get this lower since I didn't try to experement with different resistor values, I just used my 10 ohm resistor which seems to be all around pretty good.
Engaging the unloased motor running at full 4 pole speed on the stopped compressor with the magnetic clutch surges up to about 6 amps, which is lower than what I expected.
The electro magnetic clutch does offer a marginal improvement in starting amp reduction over the go cart clutch, even with the magnetic clutch having its own small inrush pull in current.
The go cart clutch increases free spin starting amps by about 10% to 20%. Using a go cart clutch is semi free spin starting since the clutch starts to engage well before the motor is up to full speed.

 

The go cart clutch is centrifugal.
The only way to adjust the clutch is to change out or alter the spring.
I changed the spring out to a much weaker one for use on the 4 pole motor.

 

If your compressor had unloaders on the head, you could wire in a solenoid that allowed activation of the unloaders while the clutch is being engaged on a delay, so the compressor is not loading in that moment.

 

the inertia of turning that fly wheel and crank shaft from stationary to full speed will always be your greatest draw loaded or not.
This is why constant speed controls work well and the continued spin helps cool the compressor between loads.
I understand what your trying to do , it's noble . and an education for sure .
One of the loads most do not consider is the belt.
Bending the belt is a load , the thicker the belt and the faster it is driven the more load is created, woking or not.
That's why they went to flat polly-groove belts for a long time . they provide more horse power to the work.
Problem is finding those belts and pulleys for this project. notice that in automotive almost all cars now have polly groove belts .
As an example bend a V belt in your hand and then one of those flat belts on the car . the motor has to bend it in motion that is a lot of load.

 

The 4 pole, 2hp magnetic clutch compressor has an unloader.
My 4 pole 1hp compressor will be getting one.
I'm going to put the compressor shut down on an adjustable time off delay so that when the mechanical unloader opens it will run for an amount of time selected by what I turn the time off delay dial to. Intermittently running the compressors where they are not getting real hot I will keep the time delay set low. When running them constantly and getting them real hot I can set the time off delay up to a minute. Which means they may not stop running at all during periods of heavy use.

I can see the advantage of those serpentine belts on a smaller pulley, the belt does offer up a good bit of hysteresis. The smallest pulley I'm using with the 4 pole motors is going to be 5 inches. The 5 and 6 inch motor pulleys I'm using will offer less hysteresis losses compared to a belt going around a typical 2 to 3.5 inch pulley used on 2 pole motor setups. But we are still talking about something like a 1% or 2% difference in efficiency.
Finding the proper size serp pulley belt for both the compressor and motor is very difficult.

 

Problem 2 is ,
Spinning te pump too fast reduces out put.
Air displacement is one thing / actual delivery is another all together
What is the recommended speed of the pump?

 

I'm keeping them all under 1,100RPM. A 6 inch pulley on a 4 pole motor turning a 10 inch compressor will only drive it at 1,077RPM. Thats if the motor had 0 slip.
They are all rated for 1,100 to 1,250 rpm and all have at least 10 inch compressor pulleys.