Motor soft starters and VFD for off grid

I figured I would post a picture of the fairly large 250hp VFD compressor at work that doesn't exist.

 

For soft starting single phase deep well submersible pumps I'm thinking the best way to do it is:
1 pump to an atmospheric or open tank, that way you are pumping against 20 to 60 less psi.
2 since you would be pumping to an open tank disable or do not install a check valve in/on the pump. That way you are not trying to start the pump again x number of feet of water. For me 108' of lift is almost 50psi.
3 there won't be any water in the line to freeze during the winter.

Now this doesn't work if you are pumping straight into a pressurized water system like most people do.

 

Do both a pressure tank and a high level gravity tank .
When the float valve on the gravity tank comes to it's limit, the rest of the load goes into the pressure tank till it's full .
When the unit starts the initial load will be marginally less till the top tank is full.
Adjust the pressure switch for the longest differential in pressure . Probably those pressures closest to the gravity tank .

 

Since it takes so little power to pressurize water from ground level to the desired pressure I will probably do a 12v off grid system pump system that way water keeps going as long as the above ground tank, aka the cistern has water in it when the power goes out.

I will test it to see what's better. Starting on a dry line versus against the water column.

 

The well service stopped by to drop off papers for my well.
I got to talking to them about well pump setups, they were saying that starting the pump on a pressure tank is hard on them.
They say they have had their good brand submersible pumps last up to 25 years when pumping to an open surface tank.

 

Why not buy a sligjtly larger and cheap 3 phase VFD from like automation direct for use on the single phase motors. Almost all the newVFDs they sell (i think fuji brand)can be used for three to single phase applications and they have soft start capability. It might cheapen up the equation.

 

Thats kindda wear I going with my comment.

 

Single phase motors can't run slower than 40 to 45hz.
The ABB VFDs will fault if hooked up for single phase, I thought all drives were like that.
I know how to program them for soft start as long as they have the capability.

 

The reason ya cant run a single phase motor slower than that is because there is a cyntrifical switch that cuts off the capacitor that simulates a 3rd power leg for start up. Didnt think about that. I think Automationdirect.com sells the single phase drives too but they only go up to like 2 or 3 hp. I have seen a few japan made AC systems that work like what you are doing but they use all three phase motors and drives in their system....... probably for that reason.

 

A 60hz motor has to get up to at least 45hz to disengage the start system.
If there was a VFD that wouldn't fault out if only 2 or the 3 phases connected or if there was a true single phase VFD out there, one could probably start the motor at 30 or 40Hz and do a 1 or 2 second ramp up to 60hz.
The second problem is almost all drives use modified sine wave, this really doesn't bother 3 phase motors that much, but single phase really doesn't like modified sine.

 

Also I think I found the best solution for softer starting single phase motors last year.

1 just going to a 1,800rpm motor substantially reduced starting inrush.

2 putting a centrifugal go cart clutch on the motor further reduced inrush.
Note, the clutches come with a spring that doesn't even start to engage the clutch till over 2,000rpm so a much weaker spring will be needed for a 1,800rpm motor.

The electromagnetic clutch worked very well but is kind of expensive.

Which is funny because I was told that I "wouldn't be able to reduce single phase starting amps".

I didn't find a way, I found more like 5 ways to reduce starting amps on single phase motor.

 

OK. All single phase motors are essentially 3 phase motors. So, try a scrape 120vac 1 phase motor and a VFD. Then, go into the motor and remove the entire starter switch and starting cap and wallah! 3 phase motor. Now you can use a 3 phase VFD and the HP rating of the motor should actually be higher after. Since singlephase motors are downplayed in horsepower because of lose of phase once up to speed. But, that may be a bit too much to mess with.

 

So far my air compressors are working great.
I use the 2hp 1800rpm air compressor with electromagnetic clutch the most.
The 1.5hp 1800rpm compressor with go cart clutch also gets used but not as much. No problems with either of them.

 

Almost 3 year later, still using that 2hp 1,800rpm electro magnetic clutch compressor rig. I think I occasionally hear it slip, might need to adjust the clutch.

 

Cold load pickup.
This is what we want to reduce especially off grid. Skip to about 13:40.

 

Cold pickup load is any load that goes from zero to full power at the flip of a switch.
For example if you ohm check a tungsten light bulb the ohms will show that while the filament is cold it will draw about 2x the amps as when it's hot.
An induction motor at rest is functionally no different than a short circuited transformer. The motor armature is your secondary winding. At rest or even over loaded, with as little as 6hz under speed the armature acts like a shorted secondary, but at full speed dipping in and out of magnetic field at no load then it's like a transformer at effectively no load.
After watching that when the power goes out I'll be sure to open all 240v breakers and keep them off for up to half an hour if possible.
I'll be sure not to plug my car in for as long as possible because switching loads back on and reenergizing line reactors will create a lot of surges.
I'll leave the solar on.

 

A trick i pulled a while back was driving a 4 cylinder Emglo pump with a 5 HP Honda engine.
Normally this pump is driven with an 8 hp or better but you use what you got.
Anyway I rigged 2 pilot controls on the pump so that all 4 cylinders are pumping in the beginning up to 60 PSI then @60 psi one unloader kicks off 2 cylinders and the engine continued to drive the pressure up to 125 and then the second pilot control disengages the second 2 cylinder and activates the throttle control as well.
If I were doing sandblasting 2 a beginning tank pressure of 120 psi and the system pressure drops to 60 psi, the pilot kicks and all 4 cylinders are producing air. Actually, 60 psi is an ideal sandblasting pressure. Make no mistake the motor is working hard pushing all 4 cylinders, but it works.